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gerrit-public.fairphone.software / platform / external / libpng / 3433e876ce57a723649d9d84635aa23394753bac / . / libpng.3
blob: db4990f339d2fe84a956abcbacdc7c7abc7ceff5 [file] [log] [blame]
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1.TH LIBPNG 3 "March 6, 2014"
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2.SH NAME
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]3libpng \- Portable Network Graphics (PNG) Reference Library 1.6.10
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4.SH SYNOPSIS
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5\fB
6#include <png.h>\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]7
8\fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
9
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]10\fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]11
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]12\fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]13
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]14\fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
15
16\fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]17
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]18\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
19
20\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
21
22\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
23
24\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
25
26\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
27
28\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
29
30\fBpng_structp png_create_read_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
31
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]32\fBpng_structp png_create_read_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]33
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]34\fBpng_structp png_create_write_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
35
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]36\fBpng_structp png_create_write_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]37
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]38\fBvoid png_data_freer (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIfreer\fP\fB, png_uint_32 \fImask)\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]39
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]40\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
41
42\fBvoid png_destroy_read_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fP\fIinfo_ptr_ptr\fP\fB, png_infopp \fIend_info_ptr_ptr\fP\fB);\fP
43
44\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
45
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]46\fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]47
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]48\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
49
50\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
51
52\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
53
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]54\fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]55
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]56\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
57
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]58\fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]59
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]60\fBpng_uint_32 png_get_bKGD (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]61
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]62\fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]63
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]64\fBpng_uint_32 png_get_cHRM (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]65
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]66\fBpng_uint_32 png_get_cHRM_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]67
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]68\fBpng_uint_32 png_get_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*red_X\fP\fB, double \fP\fI*red_Y\fP\fB, double \fP\fI*red_Z\fP\fB, double \fP\fI*green_X\fP\fB, double \fP\fI*green_Y\fP\fB, double \fP\fI*green_Z\fP\fB, double \fP\fI*blue_X\fP\fB, double \fP\fI*blue_Y\fP\fB, double \fI*blue_Z\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]69
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]70\fBpng_uint_32 png_get_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fI*int_red_X\fP\fB, png_fixed_point \fP\fI*int_red_Y\fP\fB, png_fixed_point \fP\fI*int_red_Z\fP\fB, png_fixed_point \fP\fI*int_green_X\fP\fB, png_fixed_point \fP\fI*int_green_Y\fP\fB, png_fixed_point \fP\fI*int_green_Z\fP\fB, png_fixed_point \fP\fI*int_blue_X\fP\fB, png_fixed_point \fP\fI*int_blue_Y\fP\fB, png_fixed_point \fI*int_blue_Z\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]71
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]72\fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]73
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]74\fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]75
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]76\fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]77
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]78\fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]79
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]80\fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]81
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]82\fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]83
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]84\fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]85
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]86\fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]87
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]88\fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]89
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]90\fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]91
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]92\fBpng_uint_32 png_get_gAMA (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]93
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]94\fBpng_uint_32 png_get_gAMA_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]95
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]96\fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]97
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]98\fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]99
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]100\fBpng_uint_32 png_get_hIST (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]101
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]102\fBpng_uint_32 png_get_iCCP (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_bytepp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]103
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]104\fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
105
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]106\fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]107
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]108\fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]109
110\fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
111
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]112\fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]113
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]114\fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]115
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]116\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
117
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]118\fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]119
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]120\fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]121
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]122\fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]123
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]124\fBpng_uint_32 png_get_oFFs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]125
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]126\fBpng_uint_32 png_get_pCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]127
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]128\fBpng_uint_32 png_get_pHYs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]129
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]130\fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]131
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]132\fBpng_uint_32 png_get_pHYs_dpi (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]133
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]134\fBpng_fixed_point png_get_pixel_aspect_ratio_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]135
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]136\fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]137
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]138\fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]139
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]140\fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]141
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]142\fBpng_uint_32 png_get_PLTE (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]143
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]144\fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]145
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]146\fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]147
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]148\fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]149
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]150\fBpng_uint_32 png_get_sBIT (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]151
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]152\fBvoid png_get_sCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, double* \fP\fIwidth\fP\fB, double* \fIheight\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]153
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]154\fBvoid png_get_sCAL_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_fixed_pointp \fP\fIwidth\fP\fB, png_fixed_pointp \fIheight\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]155
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]156\fBvoid png_get_sCAL_s (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_charpp \fP\fIwidth\fP\fB, png_charpp \fIheight\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]157
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]158\fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]159
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]160\fBpng_uint_32 png_get_sPLT (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]161
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]162\fBpng_uint_32 png_get_sRGB (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int \fI*file_srgb_intent\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]163
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]164\fBpng_uint_32 png_get_text (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]165
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]166\fBpng_uint_32 png_get_tIME (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]167
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]168\fBpng_uint_32 png_get_tRNS (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans_alpha\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_color\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]169
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]170\fB/* This function is really an inline macro. \fI*/
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]171
172\fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
173
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]174\fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]175
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]176\fB/* This function is really an inline macro. \fI*/
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]177
178\fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
179
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]180\fBpng_uint_32 png_get_unknown_chunks (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]181
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]182\fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]183
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]184\fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]185
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]186\fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]187
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]188\fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]189
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]190\fBpng_uint_32 png_get_valid (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]191
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]192\fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]193
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]194\fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]195
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]196\fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]197
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]198\fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]199
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]200\fBpng_uint_32 png_get_x_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]201
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]202\fBpng_uint_32 png_get_x_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]203
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]204\fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]205
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]206\fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]207
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]208\fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]209
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]210\fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]211
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]212\fBpng_uint_32 png_get_y_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]213
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]214\fBpng_uint_32 png_get_y_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]215
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]216\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
217
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]218\fBint png_image_begin_read_from_file (png_imagep \fP\fIimage\fP\fB, const char \fI*file_name\fP\fB);\fP
219
220\fBint png_image_begin_read_from_stdio (png_imagep \fP\fIimage\fP\fB, FILE* \fIfile\fP\fB);\fP
221
222\fBint, png_image_begin_read_from_memory (png_imagep \fP\fIimage\fP\fB, png_const_voidp \fP\fImemory\fP\fB, png_size_t \fIsize\fP\fB);\fP
223
224\fBint png_image_finish_read (png_imagep \fP\fIimage\fP\fB, png_colorp \fP\fIbackground\fP\fB, void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
225
226\fBvoid png_image_free (png_imagep \fIimage\fP\fB);\fP
227
228\fBint png_image_write_to_file (png_imagep \fP\fIimage\fP\fB, const char \fP\fI*file\fP\fB, int \fP\fIconvert_to_8bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
229
230\fBint png_image_write_to_stdio (png_imagep \fP\fIimage\fP\fB, FILE \fP\fI*file\fP\fB, int \fP\fIconvert_to_8_bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap)\fP\fB);\fP
231
232\fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]233
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]234\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
235
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]236\fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]237
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]238\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]239
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]240\fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]241
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]242\fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]243
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]244\fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]245
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]246\fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
247
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]248\fBpng_size_t png_process_data_pause \fP\fI(png_structp\fP\fB, int \fIsave\fP\fB);\fP
249
250\fBpng_uint_32 png_process_data_skip \fI(png_structp\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]251
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]252\fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
253
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]254\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
255
256\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
257
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]258\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
259
260\fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
261
262\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
263
264\fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
265
266\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
267
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]268\fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]269
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]270\fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]271
272\fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
273
274\fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
275
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]276\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
277
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]278\fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]279
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]280\fBvoid png_set_alpha_mode_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, png_fixed_point \fIoutput_gamma\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]281
282\fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
283
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]284\fBvoid png_set_background_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, png_uint_32 \fIbackground_gamma\fP\fB);\fP
285
286\fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]287
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]288\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
289
290\fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
291
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]292\fBvoid png_set_check_for_invalid_index(png_structrp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]293
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]294\fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
295
296\fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
297
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]298\fBvoid png_set_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIred_X\fP\fB, double \fP\fIred_Y\fP\fB, double \fP\fIred_Z\fP\fB, double \fP\fIgreen_X\fP\fB, double \fP\fIgreen_Y\fP\fB, double \fP\fIgreen_Z\fP\fB, double \fP\fIblue_X\fP\fB, double \fP\fIblue_Y\fP\fB, double \fIblue_Z\fP\fB);\fP
299
300\fBvoid png_set_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fIint_red_X\fP\fB, png_fixed_point \fP\fIint_red_Y\fP\fB, png_fixed_point \fP\fIint_red_Z\fP\fB, png_fixed_point \fP\fIint_green_X\fP\fB, png_fixed_point \fP\fIint_green_Y\fP\fB, png_fixed_point \fP\fIint_green_Z\fP\fB, png_fixed_point \fP\fIint_blue_X\fP\fB, png_fixed_point \fP\fIint_blue_Y\fP\fB, png_fixed_point \fIint_blue_Z\fP\fB);\fP
301
302\fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]303
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]304\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
305
306\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
307
308\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
309
310\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
311
312\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
313
314\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
315
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]316\fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
317
318\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
319
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]320\fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]321
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]322\fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]323
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]324\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
325
326\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
327
328\fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
329
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]330\fBvoid png_set_filter_heuristics_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_fixed_point_p \fP\fIfilter_weights\fP\fB, png_fixed_point_p \fIfilter_costs\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]331
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]332\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
333
334\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
335
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]336\fBvoid png_set_gamma_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIscreen_gamma\fP\fB, png_uint_32 \fIdefault_file_gamma\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]337
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]338\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
339
340\fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
341
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]342\fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]343
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]344\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
345
346\fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
347
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]348\fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_const_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_const_bytep \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]349
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]350\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
351
352\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
353
354\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
355
356\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
357
358\fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
359
360\fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
361
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]362\fBjmp_buf* png_set_longjmp_fn (png_structp \fP\fIpng_ptr\fP\fB, png_longjmp_ptr \fP\fIlongjmp_fn\fP\fB, size_t \fIjmp_buf_size\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]363
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]364\fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]365
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]366\fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
367
368\fBvoid png_set_mem_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]369
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]370\fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
371
372\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
373
374\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
375
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]376\fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]377
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]378\fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
379
380\fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
381
382\fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
383
384\fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
385
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]386\fBvoid png_set_quantize (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_quantize\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]387
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]388\fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
389
390\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
391
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]392\fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
393
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]394\fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
395
396\fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
397
398\fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_uint_32 \fP\fIred\fP\fB, png_uint_32 \fIgreen\fP\fB);\fP
399
400\fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
401
402\fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
403
404\fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
405
406\fBvoid png_set_sCAL_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_fixed_point \fP\fIwidth\fP\fB, png_fixed_point \fIheight\fP\fB);\fP
407
408\fBvoid png_set_sCAL_s (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_charp \fP\fIwidth\fP\fB, png_charp \fIheight\fP\fB);\fP
409
410\fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
411
412\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
413
414\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
415
416\fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
417
418\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
419
420\fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
421
422\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
423
424\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
425
426\fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
427
428\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
429
430\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
431
432\fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
433
434\fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
435
436\fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
437
438\fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
439
440\fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
441
442\fBvoid \fP\fIpng_set_text_compression_method\fP\fB, (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod)\fP\fB);\fP
443
444\fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
445
446\fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans_alpha\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_color\fP\fB);\fP
447
448\fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
449
450\fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
451
452\fBvoid png_set_unknown_chunk_location (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]453
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]454\fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
455
456\fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
457
458\fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
459
460\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
461
462\fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
463
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]464\fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
465
466\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
467
468\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
469
470\fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
471
472\fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
473
474\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
475
476\fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
477
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]478\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
479
480\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
481
482\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
483
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]484\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
485
486\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
487
488\fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
489
490\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
491
492\fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
493
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]494\fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]495
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]496.SH DESCRIPTION
497The
498.I libpng
499library supports encoding, decoding, and various manipulations of
500the Portable Network Graphics (PNG) format image files. It uses the
501.IR zlib(3)
502compression library.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]503Following is a copy of the libpng-manual.txt file that accompanies libpng.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]504.SH LIBPNG.TXT
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]505libpng-manual.txt - A description on how to use and modify libpng
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]506
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]507 libpng version 1.6.10 - March 6, 2014
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]508 Updated and distributed by Glenn Randers-Pehrson
509 <glennrp at users.sourceforge.net>
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]510 Copyright (c) 1998-2014 Glenn Randers-Pehrson
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]511
512 This document is released under the libpng license.
513 For conditions of distribution and use, see the disclaimer
514 and license in png.h
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]515
516 Based on:
517
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]518 libpng versions 0.97, January 1998, through 1.6.10 - March 6, 2014
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]519 Updated and distributed by Glenn Randers-Pehrson
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]520 Copyright (c) 1998-2014 Glenn Randers-Pehrson
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]521
522 libpng 1.0 beta 6 version 0.96 May 28, 1997
523 Updated and distributed by Andreas Dilger
524 Copyright (c) 1996, 1997 Andreas Dilger
525
526 libpng 1.0 beta 2 - version 0.88 January 26, 1996
527 For conditions of distribution and use, see copyright
528 notice in png.h. Copyright (c) 1995, 1996 Guy Eric
529 Schalnat, Group 42, Inc.
530
531 Updated/rewritten per request in the libpng FAQ
532 Copyright (c) 1995, 1996 Frank J. T. Wojcik
533 December 18, 1995 & January 20, 1996
534
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]535 TABLE OF CONTENTS
536
537 I. Introduction
538 II. Structures
539 III. Reading
540 IV. Writing
541 V. Simplified API
542 VI. Modifying/Customizing libpng
543 VII. MNG support
544 VIII. Changes to Libpng from version 0.88
545 IX. Changes to Libpng from version 1.0.x to 1.2.x
546 X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
547 XI. Changes to Libpng from version 1.4.x to 1.5.x
548 XII. Changes to Libpng from version 1.5.x to 1.6.x
549 XIII. Detecting libpng
550 XIV. Source code repository
551 XV. Coding style
552 XVI. Y2K Compliance in libpng
553
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]554.SH I. Introduction
555
556This file describes how to use and modify the PNG reference library
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]557(known as libpng) for your own use. In addition to this
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]558file, example.c is a good starting point for using the library, as
559it is heavily commented and should include everything most people
560will need. We assume that libpng is already installed; see the
561INSTALL file for instructions on how to install libpng.
562
563For examples of libpng usage, see the files "example.c", "pngtest.c",
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]564and the files in the "contrib" directory, all of which are included in
565the libpng distribution.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]566
567Libpng was written as a companion to the PNG specification, as a way
568of reducing the amount of time and effort it takes to support the PNG
569file format in application programs.
570
571The PNG specification (second edition), November 2003, is available as
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]572a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]573<http://www.w3.org/TR/2003/REC-PNG-20031110/
574The W3C and ISO documents have identical technical content.
575
576The PNG-1.2 specification is available at
577<http://www.libpng.org/pub/png/documents/>. It is technically equivalent
578to the PNG specification (second edition) but has some additional material.
579
580The PNG-1.0 specification is available
581as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
582W3C Recommendation <http://www.w3.org/TR/REC.png.html>.
583
584Some additional chunks are described in the special-purpose public chunks
585documents at <http://www.libpng.org/pub/png/documents/>.
586
587Other information
588about PNG, and the latest version of libpng, can be found at the PNG home
589page, <http://www.libpng.org/pub/png/>.
590
591Most users will not have to modify the library significantly; advanced
592users may want to modify it more. All attempts were made to make it as
593complete as possible, while keeping the code easy to understand.
594Currently, this library only supports C. Support for other languages
595is being considered.
596
597Libpng has been designed to handle multiple sessions at one time,
598to be easily modifiable, to be portable to the vast majority of
599machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
600to use. The ultimate goal of libpng is to promote the acceptance of
601the PNG file format in whatever way possible. While there is still
602work to be done (see the TODO file), libpng should cover the
603majority of the needs of its users.
604
605Libpng uses zlib for its compression and decompression of PNG files.
606Further information about zlib, and the latest version of zlib, can
607be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
608The zlib compression utility is a general purpose utility that is
609useful for more than PNG files, and can be used without libpng.
610See the documentation delivered with zlib for more details.
611You can usually find the source files for the zlib utility wherever you
612find the libpng source files.
613
614Libpng is thread safe, provided the threads are using different
615instances of the structures. Each thread should have its own
616png_struct and png_info instances, and thus its own image.
617Libpng does not protect itself against two threads using the
618same instance of a structure.
619
620.SH II. Structures
621
622There are two main structures that are important to libpng, png_struct
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]623and png_info. Both are internal structures that are no longer exposed
624in the libpng interface (as of libpng 1.5.0).
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]625
626The png_info structure is designed to provide information about the
627PNG file. At one time, the fields of png_info were intended to be
628directly accessible to the user. However, this tended to cause problems
629with applications using dynamically loaded libraries, and as a result
630a set of interface functions for png_info (the png_get_*() and png_set_*()
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]631functions) was developed, and direct access to the png_info fields was
632deprecated..
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]633
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]634The png_struct structure is the object used by the library to decode a
635single image. As of 1.5.0 this structure is also not exposed.
636
637Almost all libpng APIs require a pointer to a png_struct as the first argument.
638Many (in particular the png_set and png_get APIs) also require a pointer
639to png_info as the second argument. Some application visible macros
640defined in png.h designed for basic data access (reading and writing
641integers in the PNG format) don't take a png_info pointer, but it's almost
642always safe to assume that a (png_struct*) has to be passed to call an API
643function.
644
645You can have more than one png_info structure associated with an image,
646as illustrated in pngtest.c, one for information valid prior to the
647IDAT chunks and another (called "end_info" below) for things after them.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]648
649The png.h header file is an invaluable reference for programming with libpng.
650And while I'm on the topic, make sure you include the libpng header file:
651
652#include <png.h>
653
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]654and also (as of libpng-1.5.0) the zlib header file, if you need it:
655
656#include <zlib.h>
657
658.SS Types
659
660The png.h header file defines a number of integral types used by the
661APIs. Most of these are fairly obvious; for example types corresponding
662to integers of particular sizes and types for passing color values.
663
664One exception is how non-integral numbers are handled. For application
665convenience most APIs that take such numbers have C (double) arguments;
666however, internally PNG, and libpng, use 32 bit signed integers and encode
667the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
668macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
669which is simply (png_int_32).
670
671All APIs that take (double) arguments also have a matching API that
672takes the corresponding fixed point integer arguments. The fixed point
673API has the same name as the floating point one with "_fixed" appended.
674The actual range of values permitted in the APIs is frequently less than
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]675the full range of (png_fixed_point) (\-21474 to +21474). When APIs require
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]676a non-negative argument the type is recorded as png_uint_32 above. Consult
677the header file and the text below for more information.
678
679Special care must be take with sCAL chunk handling because the chunk itself
680uses non-integral values encoded as strings containing decimal floating point
681numbers. See the comments in the header file.
682
683.SS Configuration
684
685The main header file function declarations are frequently protected by C
686preprocessing directives of the form:
687
688 #ifdef PNG_feature_SUPPORTED
689 declare-function
690 #endif
691 ...
692 #ifdef PNG_feature_SUPPORTED
693 use-function
694 #endif
695
696The library can be built without support for these APIs, although a
697standard build will have all implemented APIs. Application programs
698should check the feature macros before using an API for maximum
699portability. From libpng 1.5.0 the feature macros set during the build
700of libpng are recorded in the header file "pnglibconf.h" and this file
701is always included by png.h.
702
703If you don't need to change the library configuration from the default, skip to
704the next section ("Reading").
705
706Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
707of the build project files in the 'projects' directory simply copy
708scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
709systems do not permit easy auto-configuration of the library - they only
710support the default configuration.
711
712The easiest way to make minor changes to the libpng configuration when
713auto-configuration is supported is to add definitions to the command line
714using (typically) CPPFLAGS. For example:
715
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]716CPPFLAGS=\-DPNG_NO_FLOATING_ARITHMETIC
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]717
718will change the internal libpng math implementation for gamma correction and
719other arithmetic calculations to fixed point, avoiding the need for fast
720floating point support. The result can be seen in the generated pnglibconf.h -
721make sure it contains the changed feature macro setting.
722
723If you need to make more extensive configuration changes - more than one or two
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]724feature macro settings - you can either add \-DPNG_USER_CONFIG to the build
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]725command line and put a list of feature macro settings in pngusr.h or you can set
726DFA_XTRA (a makefile variable) to a file containing the same information in the
727form of 'option' settings.
728
729A. Changing pnglibconf.h
730
731A variety of methods exist to build libpng. Not all of these support
732reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
733rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
734
735Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
736pnglibconf.h and changing the lines defining the supported features, paying
737very close attention to the 'option' information in scripts/pnglibconf.dfa
738that describes those features and their requirements. This is easy to get
739wrong.
740
741B. Configuration using DFA_XTRA
742
743Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
744variant such as 'nawk' or 'gawk', is available. The configure build will
745automatically find an appropriate awk and build pnglibconf.h.
746The scripts/pnglibconf.mak file contains a set of make rules for doing the
747same thing if configure is not used, and many of the makefiles in the scripts
748directory use this approach.
749
750When rebuilding simply write a new file containing changed options and set
751DFA_XTRA to the name of this file. This causes the build to append the new file
752to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
753of the following forms:
754
755everything = off
756
757This turns all optional features off. Include it at the start of pngusr.dfa to
758make it easier to build a minimal configuration. You will need to turn at least
759some features on afterward to enable either reading or writing code, or both.
760
761option feature on
762option feature off
763
764Enable or disable a single feature. This will automatically enable other
765features required by a feature that is turned on or disable other features that
766require a feature which is turned off. Conflicting settings will cause an error
767message to be emitted by awk.
768
769setting feature default value
770
771Changes the default value of setting 'feature' to 'value'. There are a small
772number of settings listed at the top of pnglibconf.h, they are documented in the
773source code. Most of these values have performance implications for the library
774but most of them have no visible effect on the API. Some can also be overridden
775from the API.
776
777This method of building a customized pnglibconf.h is illustrated in
778contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
779pngusr.dfa in these directories.
780
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]781C. Configuration using PNG_USER_CONFIG
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]782
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]783If \-DPNG_USER_CONFIG is added to the CPPFLAGS when pnglibconf.h is built,
784the file pngusr.h will automatically be included before the options in
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]785scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
786macro definitions turning features on or off or setting settings.
787
788Apart from the global setting "everything = off" all the options listed above
789can be set using macros in pngusr.h:
790
791#define PNG_feature_SUPPORTED
792
793is equivalent to:
794
795option feature on
796
797#define PNG_NO_feature
798
799is equivalent to:
800
801option feature off
802
803#define PNG_feature value
804
805is equivalent to:
806
807setting feature default value
808
809Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
810pngusr file you supply override the contents of scripts/pnglibconf.dfa
811
812If confusing or incomprehensible behavior results it is possible to
813examine the intermediate file pnglibconf.dfn to find the full set of
814dependency information for each setting and option. Simply locate the
815feature in the file and read the C comments that precede it.
816
817This method is also illustrated in the contrib/pngminim/* makefiles and
818pngusr.h.
819
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]820.SH III. Reading
821
822We'll now walk you through the possible functions to call when reading
823in a PNG file sequentially, briefly explaining the syntax and purpose
824of each one. See example.c and png.h for more detail. While
825progressive reading is covered in the next section, you will still
826need some of the functions discussed in this section to read a PNG
827file.
828
829.SS Setup
830
831You will want to do the I/O initialization(*) before you get into libpng,
832so if it doesn't work, you don't have much to undo. Of course, you
833will also want to insure that you are, in fact, dealing with a PNG
834file. Libpng provides a simple check to see if a file is a PNG file.
835To use it, pass in the first 1 to 8 bytes of the file to the function
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]836png_sig_cmp(), and it will return 0 (false) if the bytes match the
837corresponding bytes of the PNG signature, or nonzero (true) otherwise.
838Of course, the more bytes you pass in, the greater the accuracy of the
839prediction.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]840
841If you are intending to keep the file pointer open for use in libpng,
842you must ensure you don't read more than 8 bytes from the beginning
843of the file, and you also have to make a call to png_set_sig_bytes_read()
844with the number of bytes you read from the beginning. Libpng will
845then only check the bytes (if any) that your program didn't read.
846
847(*): If you are not using the standard I/O functions, you will need
848to replace them with custom functions. See the discussion under
849Customizing libpng.
850
851
852 FILE *fp = fopen(file_name, "rb");
853 if (!fp)
854 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]855 return (ERROR);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]856 }
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]857
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]858 fread(header, 1, number, fp);
859 is_png = !png_sig_cmp(header, 0, number);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]860
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]861 if (!is_png)
862 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]863 return (NOT_PNG);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]864 }
865
866
867Next, png_struct and png_info need to be allocated and initialized. In
868order to ensure that the size of these structures is correct even with a
869dynamically linked libpng, there are functions to initialize and
870allocate the structures. We also pass the library version, optional
871pointers to error handling functions, and a pointer to a data struct for
872use by the error functions, if necessary (the pointer and functions can
873be NULL if the default error handlers are to be used). See the section
874on Changes to Libpng below regarding the old initialization functions.
875The structure allocation functions quietly return NULL if they fail to
876create the structure, so your application should check for that.
877
878 png_structp png_ptr = png_create_read_struct
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]879 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]880 user_error_fn, user_warning_fn);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]881
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]882 if (!png_ptr)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]883 return (ERROR);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]884
885 png_infop info_ptr = png_create_info_struct(png_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]886
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]887 if (!info_ptr)
888 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]889 png_destroy_read_struct(&png_ptr,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]890 (png_infopp)NULL, (png_infopp)NULL);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]891 return (ERROR);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]892 }
893
894If you want to use your own memory allocation routines,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]895use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]896png_create_read_struct_2() instead of png_create_read_struct():
897
898 png_structp png_ptr = png_create_read_struct_2
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]899 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]900 user_error_fn, user_warning_fn, (png_voidp)
901 user_mem_ptr, user_malloc_fn, user_free_fn);
902
903The error handling routines passed to png_create_read_struct()
904and the memory alloc/free routines passed to png_create_struct_2()
905are only necessary if you are not using the libpng supplied error
906handling and memory alloc/free functions.
907
908When libpng encounters an error, it expects to longjmp back
909to your routine. Therefore, you will need to call setjmp and pass
910your png_jmpbuf(png_ptr). If you read the file from different
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]911routines, you will need to update the longjmp buffer every time you enter
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]912a new routine that will call a png_*() function.
913
914See your documentation of setjmp/longjmp for your compiler for more
915information on setjmp/longjmp. See the discussion on libpng error
916handling in the Customizing Libpng section below for more information
917on the libpng error handling. If an error occurs, and libpng longjmp's
918back to your setjmp, you will want to call png_destroy_read_struct() to
919free any memory.
920
921 if (setjmp(png_jmpbuf(png_ptr)))
922 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]923 png_destroy_read_struct(&png_ptr, &info_ptr,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]924 &end_info);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]925 fclose(fp);
926 return (ERROR);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]927 }
928
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]929Pass (png_infopp)NULL instead of &end_info if you didn't create
930an end_info structure.
931
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]932If you would rather avoid the complexity of setjmp/longjmp issues,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]933you can compile libpng with PNG_NO_SETJMP, in which case
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]934errors will result in a call to PNG_ABORT() which defaults to abort().
935
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]936You can #define PNG_ABORT() to a function that does something
937more useful than abort(), as long as your function does not
938return.
939
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]940Now you need to set up the input code. The default for libpng is to
941use the C function fread(). If you use this, you will need to pass a
942valid FILE * in the function png_init_io(). Be sure that the file is
943opened in binary mode. If you wish to handle reading data in another
944way, you need not call the png_init_io() function, but you must then
945implement the libpng I/O methods discussed in the Customizing Libpng
946section below.
947
948 png_init_io(png_ptr, fp);
949
950If you had previously opened the file and read any of the signature from
951the beginning in order to see if this was a PNG file, you need to let
952libpng know that there are some bytes missing from the start of the file.
953
954 png_set_sig_bytes(png_ptr, number);
955
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]956You can change the zlib compression buffer size to be used while
957reading compressed data with
958
959 png_set_compression_buffer_size(png_ptr, buffer_size);
960
961where the default size is 8192 bytes. Note that the buffer size
962is changed immediately and the buffer is reallocated immediately,
963instead of setting a flag to be acted upon later.
964
965If you want CRC errors to be handled in a different manner than
966the default, use
967
968 png_set_crc_action(png_ptr, crit_action, ancil_action);
969
970The values for png_set_crc_action() say how libpng is to handle CRC errors in
971ancillary and critical chunks, and whether to use the data contained
972therein. Note that it is impossible to "discard" data in a critical
973chunk.
974
975Choices for (int) crit_action are
976 PNG_CRC_DEFAULT 0 error/quit
977 PNG_CRC_ERROR_QUIT 1 error/quit
978 PNG_CRC_WARN_USE 3 warn/use data
979 PNG_CRC_QUIET_USE 4 quiet/use data
980 PNG_CRC_NO_CHANGE 5 use the current value
981
982Choices for (int) ancil_action are
983 PNG_CRC_DEFAULT 0 error/quit
984 PNG_CRC_ERROR_QUIT 1 error/quit
985 PNG_CRC_WARN_DISCARD 2 warn/discard data
986 PNG_CRC_WARN_USE 3 warn/use data
987 PNG_CRC_QUIET_USE 4 quiet/use data
988 PNG_CRC_NO_CHANGE 5 use the current value
989
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]990.SS Setting up callback code
991
992You can set up a callback function to handle any unknown chunks in the
993input stream. You must supply the function
994
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]995 read_chunk_callback(png_structp png_ptr,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]996 png_unknown_chunkp chunk);
997 {
998 /* The unknown chunk structure contains your
999 chunk data, along with similar data for any other
1000 unknown chunks: */
1001
1002 png_byte name[5];
1003 png_byte *data;
1004 png_size_t size;
1005
1006 /* Note that libpng has already taken care of
1007 the CRC handling */
1008
1009 /* put your code here. Search for your chunk in the
1010 unknown chunk structure, process it, and return one
1011 of the following: */
1012
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1013 return (\-n); /* chunk had an error */
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1014 return (0); /* did not recognize */
1015 return (n); /* success */
1016 }
1017
1018(You can give your function another name that you like instead of
1019"read_chunk_callback")
1020
1021To inform libpng about your function, use
1022
1023 png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
1024 read_chunk_callback);
1025
1026This names not only the callback function, but also a user pointer that
1027you can retrieve with
1028
1029 png_get_user_chunk_ptr(png_ptr);
1030
1031If you call the png_set_read_user_chunk_fn() function, then all unknown
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1032chunks which the callback does not handle will be saved when read. You can
1033cause them to be discarded by returning '1' ("handled") instead of '0'. This
1034behavior will change in libpng 1.7 and the default handling set by the
1035png_set_keep_unknown_chunks() function, described below, will be used when the
1036callback returns 0. If you want the existing behavior you should set the global
1037default to PNG_HANDLE_CHUNK_IF_SAFE now; this is compatible with all current
1038versions of libpng and with 1.7. Libpng 1.6 issues a warning if you keep the
1039default, or PNG_HANDLE_CHUNK_NEVER, and the callback returns 0.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1040
1041At this point, you can set up a callback function that will be
1042called after each row has been read, which you can use to control
1043a progress meter or the like. It's demonstrated in pngtest.c.
1044You must supply a function
1045
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1046 void read_row_callback(png_structp png_ptr,
1047 png_uint_32 row, int pass);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1048 {
1049 /* put your code here */
1050 }
1051
1052(You can give it another name that you like instead of "read_row_callback")
1053
1054To inform libpng about your function, use
1055
1056 png_set_read_status_fn(png_ptr, read_row_callback);
1057
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1058When this function is called the row has already been completely processed and
1059the 'row' and 'pass' refer to the next row to be handled. For the
1060non-interlaced case the row that was just handled is simply one less than the
1061passed in row number, and pass will always be 0. For the interlaced case the
1062same applies unless the row value is 0, in which case the row just handled was
1063the last one from one of the preceding passes. Because interlacing may skip a
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1064pass you cannot be sure that the preceding pass is just 'pass\-1', if you really
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1065need to know what the last pass is record (row,pass) from the callback and use
1066the last recorded value each time.
1067
1068As with the user transform you can find the output row using the
1069PNG_ROW_FROM_PASS_ROW macro.
1070
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1071.SS Unknown-chunk handling
1072
1073Now you get to set the way the library processes unknown chunks in the
1074input PNG stream. Both known and unknown chunks will be read. Normal
1075behavior is that known chunks will be parsed into information in
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]1076various info_ptr members while unknown chunks will be discarded. This
1077behavior can be wasteful if your application will never use some known
1078chunk types. To change this, you can call:
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1079
1080 png_set_keep_unknown_chunks(png_ptr, keep,
1081 chunk_list, num_chunks);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1082
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1083 keep - 0: default unknown chunk handling
1084 1: ignore; do not keep
1085 2: keep only if safe-to-copy
1086 3: keep even if unsafe-to-copy
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1087
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1088 You can use these definitions:
1089 PNG_HANDLE_CHUNK_AS_DEFAULT 0
1090 PNG_HANDLE_CHUNK_NEVER 1
1091 PNG_HANDLE_CHUNK_IF_SAFE 2
1092 PNG_HANDLE_CHUNK_ALWAYS 3
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1093
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1094 chunk_list - list of chunks affected (a byte string,
1095 five bytes per chunk, NULL or '\0' if
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1096 num_chunks is positive; ignored if
1097 numchunks <= 0).
1098
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1099 num_chunks - number of chunks affected; if 0, all
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1100 unknown chunks are affected. If positive,
1101 only the chunks in the list are affected,
1102 and if negative all unknown chunks and
1103 all known chunks except for the IHDR,
1104 PLTE, tRNS, IDAT, and IEND chunks are
1105 affected.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1106
1107Unknown chunks declared in this way will be saved as raw data onto a
1108list of png_unknown_chunk structures. If a chunk that is normally
1109known to libpng is named in the list, it will be handled as unknown,
1110according to the "keep" directive. If a chunk is named in successive
1111instances of png_set_keep_unknown_chunks(), the final instance will
1112take precedence. The IHDR and IEND chunks should not be named in
1113chunk_list; if they are, libpng will process them normally anyway.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1114If you know that your application will never make use of some particular
1115chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1116
1117Here is an example of the usage of png_set_keep_unknown_chunks(),
1118where the private "vpAg" chunk will later be processed by a user chunk
1119callback function:
1120
1121 png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
1122
1123 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
1124 png_byte unused_chunks[]=
1125 {
1126 104, 73, 83, 84, (png_byte) '\0', /* hIST */
1127 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
1128 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
1129 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
1130 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
1131 116, 73, 77, 69, (png_byte) '\0', /* tIME */
1132 };
1133 #endif
1134
1135 ...
1136
1137 #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1138 /* ignore all unknown chunks
1139 * (use global setting "2" for libpng16 and earlier):
1140 */
1141 png_set_keep_unknown_chunks(read_ptr, 2, NULL, 0);
1142
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1143 /* except for vpAg: */
1144 png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1145
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1146 /* also ignore unused known chunks: */
1147 png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1148 (int)(sizeof unused_chunks)/5);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1149 #endif
1150
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]1151.SS User limits
1152
1153The PNG specification allows the width and height of an image to be as
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1154large as 2^(31\-1 (0x7fffffff), or about 2.147 billion rows and columns.
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]1155Since very few applications really need to process such large images,
1156we have imposed an arbitrary 1-million limit on rows and columns.
1157Larger images will be rejected immediately with a png_error() call. If
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1158you wish to change this limit, you can use
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]1159
1160 png_set_user_limits(png_ptr, width_max, height_max);
1161
1162to set your own limits, or use width_max = height_max = 0x7fffffffL
1163to allow all valid dimensions (libpng may reject some very large images
1164anyway because of potential buffer overflow conditions).
1165
1166You should put this statement after you create the PNG structure and
1167before calling png_read_info(), png_read_png(), or png_process_data().
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1168
1169When writing a PNG datastream, put this statement before calling
1170png_write_info() or png_write_png().
1171
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]1172If you need to retrieve the limits that are being applied, use
1173
1174 width_max = png_get_user_width_max(png_ptr);
1175 height_max = png_get_user_height_max(png_ptr);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1176
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1177The PNG specification sets no limit on the number of ancillary chunks
1178allowed in a PNG datastream. You can impose a limit on the total number
1179of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
1180
1181 png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
1182
1183where 0x7fffffffL means unlimited. You can retrieve this limit with
1184
1185 chunk_cache_max = png_get_chunk_cache_max(png_ptr);
1186
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1187You can also set a limit on the amount of memory that a compressed chunk
1188other than IDAT can occupy, with
1189
1190 png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
1191
1192and you can retrieve the limit with
1193
1194 chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
1195
1196Any chunks that would cause either of these limits to be exceeded will
1197be ignored.
1198
1199.SS Information about your system
1200
1201If you intend to display the PNG or to incorporate it in other image data you
1202need to tell libpng information about your display or drawing surface so that
1203libpng can convert the values in the image to match the display.
1204
1205From libpng-1.5.4 this information can be set before reading the PNG file
1206header. In earlier versions png_set_gamma() existed but behaved incorrectly if
1207called before the PNG file header had been read and png_set_alpha_mode() did not
1208exist.
1209
1210If you need to support versions prior to libpng-1.5.4 test the version number
1211as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
1212described in the appropriate manual page.
1213
1214You give libpng the encoding expected by your system expressed as a 'gamma'
1215value. You can also specify a default encoding for the PNG file in
1216case the required information is missing from the file. By default libpng
1217assumes that the PNG data matches your system, to keep this default call:
1218
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1219 png_set_gamma(png_ptr, screen_gamma, output_gamma);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1220
1221or you can use the fixed point equivalent:
1222
1223 png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma,
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1224 PNG_FP_1*output_gamma);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1225
1226If you don't know the gamma for your system it is probably 2.2 - a good
1227approximation to the IEC standard for display systems (sRGB). If images are
1228too contrasty or washed out you got the value wrong - check your system
1229documentation!
1230
1231Many systems permit the system gamma to be changed via a lookup table in the
1232display driver, a few systems, including older Macs, change the response by
1233default. As of 1.5.4 three special values are available to handle common
1234situations:
1235
1236 PNG_DEFAULT_sRGB: Indicates that the system conforms to the
1237 IEC 61966-2-1 standard. This matches almost
1238 all systems.
1239 PNG_GAMMA_MAC_18: Indicates that the system is an older
1240 (pre Mac OS 10.6) Apple Macintosh system with
1241 the default settings.
1242 PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates
1243 that the system expects data with no gamma
1244 encoding.
1245
1246You would use the linear (unencoded) value if you need to process the pixel
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1247values further because this avoids the need to decode and re-encode each
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1248component value whenever arithmetic is performed. A lot of graphics software
1249uses linear values for this reason, often with higher precision component values
1250to preserve overall accuracy.
1251
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1252
1253The output_gamma value expresses how to decode the output values, not how
1254they are encoded. The values used correspond to the normal numbers used to
1255describe the overall gamma of a computer display system; for example 2.2 for
1256an sRGB conformant system. The values are scaled by 100000 in the _fixed
1257version of the API (so 220000 for sRGB.)
1258
1259The inverse of the value is always used to provide a default for the PNG file
1260encoding if it has no gAMA chunk and if png_set_gamma() has not been called
1261to override the PNG gamma information.
1262
1263When the ALPHA_OPTIMIZED mode is selected the output gamma is used to encode
1264opaque pixels however pixels with lower alpha values are not encoded,
1265regardless of the output gamma setting.
1266
1267When the standard Porter Duff handling is requested with mode 1 the output
1268encoding is set to be linear and the output_gamma value is only relevant
1269as a default for input data that has no gamma information. The linear output
1270encoding will be overridden if png_set_gamma() is called - the results may be
1271highly unexpected!
1272
1273The following numbers are derived from the sRGB standard and the research
1274behind it. sRGB is defined to be approximated by a PNG gAMA chunk value of
12750.45455 (1/2.2) for PNG. The value implicitly includes any viewing
1276correction required to take account of any differences in the color
1277environment of the original scene and the intended display environment; the
1278value expresses how to *decode* the image for display, not how the original
1279data was *encoded*.
1280
1281sRGB provides a peg for the PNG standard by defining a viewing environment.
1282sRGB itself, and earlier TV standards, actually use a more complex transform
1283(a linear portion then a gamma 2.4 power law) than PNG can express. (PNG is
1284limited to simple power laws.) By saying that an image for direct display on
1285an sRGB conformant system should be stored with a gAMA chunk value of 45455
1286(11.3.3.2 and 11.3.3.5 of the ISO PNG specification) the PNG specification
1287makes it possible to derive values for other display systems and
1288environments.
1289
1290The Mac value is deduced from the sRGB based on an assumption that the actual
1291extra viewing correction used in early Mac display systems was implemented as
1292a power 1.45 lookup table.
1293
1294Any system where a programmable lookup table is used or where the behavior of
1295the final display device characteristics can be changed requires system
1296specific code to obtain the current characteristic. However this can be
1297difficult and most PNG gamma correction only requires an approximate value.
1298
1299By default, if png_set_alpha_mode() is not called, libpng assumes that all
1300values are unencoded, linear, values and that the output device also has a
1301linear characteristic. This is only very rarely correct - it is invariably
1302better to call png_set_alpha_mode() with PNG_DEFAULT_sRGB than rely on the
1303default if you don't know what the right answer is!
1304
1305The special value PNG_GAMMA_MAC_18 indicates an older Mac system (pre Mac OS
130610.6) which used a correction table to implement a somewhat lower gamma on an
1307otherwise sRGB system.
1308
1309Both these values are reserved (not simple gamma values) in order to allow
1310more precise correction internally in the future.
1311
1312NOTE: the values can be passed to either the fixed or floating
1313point APIs, but the floating point API will also accept floating point
1314values.
1315
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1316The second thing you may need to tell libpng about is how your system handles
1317alpha channel information. Some, but not all, PNG files contain an alpha
1318channel. To display these files correctly you need to compose the data onto a
1319suitable background, as described in the PNG specification.
1320
1321Libpng only supports composing onto a single color (using png_set_background;
1322see below). Otherwise you must do the composition yourself and, in this case,
1323you may need to call png_set_alpha_mode:
1324
1325 #if PNG_LIBPNG_VER >= 10504
1326 png_set_alpha_mode(png_ptr, mode, screen_gamma);
1327 #else
1328 png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
1329 #endif
1330
1331The screen_gamma value is the same as the argument to png_set_gamma; however,
1332how it affects the output depends on the mode. png_set_alpha_mode() sets the
1333file gamma default to 1/screen_gamma, so normally you don't need to call
1334png_set_gamma. If you need different defaults call png_set_gamma() before
1335png_set_alpha_mode() - if you call it after it will override the settings made
1336by png_set_alpha_mode().
1337
1338The mode is as follows:
1339
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1340 PNG_ALPHA_PNG: The data is encoded according to the PNG
1341specification. Red, green and blue, or gray, components are
1342gamma encoded color values and are not premultiplied by the
1343alpha value. The alpha value is a linear measure of the
1344contribution of the pixel to the corresponding final output pixel.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1345
1346You should normally use this format if you intend to perform
1347color correction on the color values; most, maybe all, color
1348correction software has no handling for the alpha channel and,
1349anyway, the math to handle pre-multiplied component values is
1350unnecessarily complex.
1351
1352Before you do any arithmetic on the component values you need
1353to remove the gamma encoding and multiply out the alpha
1354channel. See the PNG specification for more detail. It is
1355important to note that when an image with an alpha channel is
1356scaled, linear encoded, pre-multiplied component values must
1357be used!
1358
1359The remaining modes assume you don't need to do any further color correction or
1360that if you do, your color correction software knows all about alpha (it
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1361probably doesn't!). They 'associate' the alpha with the color information by
1362storing color channel values that have been scaled by the alpha. The
1363advantage is that the color channels can be resampled (the image can be
1364scaled) in this form. The disadvantage is that normal practice is to store
1365linear, not (gamma) encoded, values and this requires 16-bit channels for
1366still images rather than the 8-bit channels that are just about sufficient if
1367gamma encoding is used. In addition all non-transparent pixel values,
1368including completely opaque ones, must be gamma encoded to produce the final
1369image. These are the 'STANDARD', 'ASSOCIATED' or 'PREMULTIPLIED' modes
1370described below (the latter being the two common names for associated alpha
1371color channels). Note that PNG files always contain non-associated color
1372channels; png_set_alpha_mode() with one of the modes causes the decoder to
1373convert the pixels to an associated form before returning them to your
1374application.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1375
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1376Since it is not necessary to perform arithmetic on opaque color values so
1377long as they are not to be resampled and are in the final color space it is
1378possible to optimize the handling of alpha by storing the opaque pixels in
1379the PNG format (adjusted for the output color space) while storing partially
1380opaque pixels in the standard, linear, format. The accuracy required for
1381standard alpha composition is relatively low, because the pixels are
1382isolated, therefore typically the accuracy loss in storing 8-bit linear
1383values is acceptable. (This is not true if the alpha channel is used to
1384simulate transparency over large areas - use 16 bits or the PNG mode in
1385this case!) This is the 'OPTIMIZED' mode. For this mode a pixel is
1386treated as opaque only if the alpha value is equal to the maximum value.
1387
1388 PNG_ALPHA_STANDARD: The data libpng produces is encoded in the
1389standard way assumed by most correctly written graphics software.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1390The gamma encoding will be removed by libpng and the
1391linear component values will be pre-multiplied by the
1392alpha channel.
1393
1394With this format the final image must be re-encoded to
1395match the display gamma before the image is displayed.
1396If your system doesn't do that, yet still seems to
1397perform arithmetic on the pixels without decoding them,
1398it is broken - check out the modes below.
1399
1400With PNG_ALPHA_STANDARD libpng always produces linear
1401component values, whatever screen_gamma you supply. The
1402screen_gamma value is, however, used as a default for
1403the file gamma if the PNG file has no gamma information.
1404
1405If you call png_set_gamma() after png_set_alpha_mode() you
1406will override the linear encoding. Instead the
1407pre-multiplied pixel values will be gamma encoded but
1408the alpha channel will still be linear. This may
1409actually match the requirements of some broken software,
1410but it is unlikely.
1411
1412While linear 8-bit data is often used it has
1413insufficient precision for any image with a reasonable
1414dynamic range. To avoid problems, and if your software
1415supports it, use png_set_expand_16() to force all
1416components to 16 bits.
1417
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1418 PNG_ALPHA_OPTIMIZED: This mode is the same as PNG_ALPHA_STANDARD
1419except that completely opaque pixels are gamma encoded according to
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1420the screen_gamma value. Pixels with alpha less than 1.0
1421will still have linear components.
1422
1423Use this format if you have control over your
1424compositing software and so don't do other arithmetic
1425(such as scaling) on the data you get from libpng. Your
1426compositing software can simply copy opaque pixels to
1427the output but still has linear values for the
1428non-opaque pixels.
1429
1430In normal compositing, where the alpha channel encodes
1431partial pixel coverage (as opposed to broad area
1432translucency), the inaccuracies of the 8-bit
1433representation of non-opaque pixels are irrelevant.
1434
1435You can also try this format if your software is broken;
1436it might look better.
1437
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1438 PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD; however, all component
1439values, including the alpha channel are gamma encoded. This is
1440broken because, in practice, no implementation that uses this choice
1441correctly undoes the encoding before handling alpha composition. Use this
1442choice only if other serious errors in the software or hardware you use
1443mandate it. In most cases of broken software or hardware the bug in the
1444final display manifests as a subtle halo around composited parts of the
1445image. You may not even perceive this as a halo; the composited part of
1446the image may simply appear separate from the background, as though it had
1447been cut out of paper and pasted on afterward.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1448
1449If you don't have to deal with bugs in software or hardware, or if you can fix
1450them, there are three recommended ways of using png_set_alpha_mode():
1451
1452 png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
1453 screen_gamma);
1454
1455You can do color correction on the result (libpng does not currently
1456support color correction internally). When you handle the alpha channel
1457you need to undo the gamma encoding and multiply out the alpha.
1458
1459 png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
1460 screen_gamma);
1461 png_set_expand_16(png_ptr);
1462
1463If you are using the high level interface, don't call png_set_expand_16();
1464instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
1465
1466With this mode you can't do color correction, but you can do arithmetic,
1467including composition and scaling, on the data without further processing.
1468
1469 png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
1470 screen_gamma);
1471
1472You can avoid the expansion to 16-bit components with this mode, but you
1473lose the ability to scale the image or perform other linear arithmetic.
1474All you can do is compose the result onto a matching output. Since this
1475mode is libpng-specific you also need to write your own composition
1476software.
1477
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1478The following are examples of calls to png_set_alpha_mode to achieve the
1479required overall gamma correction and, where necessary, alpha
1480premultiplication.
1481
1482 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
1483
1484This is the default libpng handling of the alpha channel - it is not
1485pre-multiplied into the color components. In addition the call states
1486that the output is for a sRGB system and causes all PNG files without gAMA
1487chunks to be assumed to be encoded using sRGB.
1488
1489 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
1490
1491In this case the output is assumed to be something like an sRGB conformant
1492display preceeded by a power-law lookup table of power 1.45. This is how
1493early Mac systems behaved.
1494
1495 png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_GAMMA_LINEAR);
1496
1497This is the classic Jim Blinn approach and will work in academic
1498environments where everything is done by the book. It has the shortcoming
1499of assuming that input PNG data with no gamma information is linear - this
1500is unlikely to be correct unless the PNG files where generated locally.
1501Most of the time the output precision will be so low as to show
1502significant banding in dark areas of the image.
1503
1504 png_set_expand_16(pp);
1505 png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_DEFAULT_sRGB);
1506
1507This is a somewhat more realistic Jim Blinn inspired approach. PNG files
1508are assumed to have the sRGB encoding if not marked with a gamma value and
1509the output is always 16 bits per component. This permits accurate scaling
1510and processing of the data. If you know that your input PNG files were
1511generated locally you might need to replace PNG_DEFAULT_sRGB with the
1512correct value for your system.
1513
1514 png_set_alpha_mode(pp, PNG_ALPHA_OPTIMIZED, PNG_DEFAULT_sRGB);
1515
1516If you just need to composite the PNG image onto an existing background
1517and if you control the code that does this you can use the optimization
1518setting. In this case you just copy completely opaque pixels to the
1519output. For pixels that are not completely transparent (you just skip
1520those) you do the composition math using png_composite or png_composite_16
1521below then encode the resultant 8-bit or 16-bit values to match the output
1522encoding.
1523
1524 Other cases
1525
1526If neither the PNG nor the standard linear encoding work for you because
1527of the software or hardware you use then you have a big problem. The PNG
1528case will probably result in halos around the image. The linear encoding
1529will probably result in a washed out, too bright, image (it's actually too
1530contrasty.) Try the ALPHA_OPTIMIZED mode above - this will probably
1531substantially reduce the halos. Alternatively try:
1532
1533 png_set_alpha_mode(pp, PNG_ALPHA_BROKEN, PNG_DEFAULT_sRGB);
1534
1535This option will also reduce the halos, but there will be slight dark
1536halos round the opaque parts of the image where the background is light.
1537In the OPTIMIZED mode the halos will be light halos where the background
1538is dark. Take your pick - the halos are unavoidable unless you can get
1539your hardware/software fixed! (The OPTIMIZED approach is slightly
1540faster.)
1541
1542When the default gamma of PNG files doesn't match the output gamma.
1543If you have PNG files with no gamma information png_set_alpha_mode allows
1544you to provide a default gamma, but it also sets the ouput gamma to the
1545matching value. If you know your PNG files have a gamma that doesn't
1546match the output you can take advantage of the fact that
1547png_set_alpha_mode always sets the output gamma but only sets the PNG
1548default if it is not already set:
1549
1550 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
1551 png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
1552
1553The first call sets both the default and the output gamma values, the
1554second call overrides the output gamma without changing the default. This
1555is easier than achieving the same effect with png_set_gamma. You must use
1556PNG_ALPHA_PNG for the first call - internal checking in png_set_alpha will
1557fire if more than one call to png_set_alpha_mode and png_set_background is
1558made in the same read operation, however multiple calls with PNG_ALPHA_PNG
1559are ignored.
1560
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1561If you don't need, or can't handle, the alpha channel you can call
1562png_set_background() to remove it by compositing against a fixed color. Don't
1563call png_set_strip_alpha() to do this - it will leave spurious pixel values in
1564transparent parts of this image.
1565
1566 png_set_background(png_ptr, &background_color,
1567 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
1568
1569The background_color is an RGB or grayscale value according to the data format
1570libpng will produce for you. Because you don't yet know the format of the PNG
1571file, if you call png_set_background at this point you must arrange for the
1572format produced by libpng to always have 8-bit or 16-bit components and then
1573store the color as an 8-bit or 16-bit color as appropriate. The color contains
1574separate gray and RGB component values, so you can let libpng produce gray or
1575RGB output according to the input format, but low bit depth grayscale images
1576must always be converted to at least 8-bit format. (Even though low bit depth
1577grayscale images can't have an alpha channel they can have a transparent
1578color!)
1579
1580You set the transforms you need later, either as flags to the high level
1581interface or libpng API calls for the low level interface. For reference the
1582settings and API calls required are:
1583
15848-bit values:
1585 PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
1586 png_set_expand(png_ptr); png_set_scale_16(png_ptr);
1587
1588 If you must get exactly the same inaccurate results
1589 produced by default in versions prior to libpng-1.5.4,
1590 use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
1591 instead.
1592
159316-bit values:
1594 PNG_TRANSFORM_EXPAND_16
1595 png_set_expand_16(png_ptr);
1596
1597In either case palette image data will be expanded to RGB. If you just want
1598color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
1599to the list.
1600
1601Calling png_set_background before the PNG file header is read will not work
1602prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
1603errors it is therefore much safer to call png_set_background after the head has
1604been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
1605used with the high level interface.
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1606
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1607.SS The high-level read interface
1608
1609At this point there are two ways to proceed; through the high-level
1610read interface, or through a sequence of low-level read operations.
1611You can use the high-level interface if (a) you are willing to read
1612the entire image into memory, and (b) the input transformations
1613you want to do are limited to the following set:
1614
1615 PNG_TRANSFORM_IDENTITY No transformation
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1616 PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
1617 8-bit accurately
1618 PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
1619 8-bit less accurately
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1620 PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
1621 PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
1622 samples to bytes
1623 PNG_TRANSFORM_PACKSWAP Change order of packed
1624 pixels to LSB first
1625 PNG_TRANSFORM_EXPAND Perform set_expand()
1626 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
1627 PNG_TRANSFORM_SHIFT Normalize pixels to the
1628 sBIT depth
1629 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
1630 to BGRA
1631 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
1632 to AG
1633 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
1634 to transparency
1635 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1636 PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
1637 to RGB (or GA to RGBA)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1638 PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1639
1640(This excludes setting a background color, doing gamma transformation,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1641quantizing, and setting filler.) If this is the case, simply do this:
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1642
1643 png_read_png(png_ptr, info_ptr, png_transforms, NULL)
1644
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1645where png_transforms is an integer containing the bitwise OR of some
1646set of transformation flags. This call is equivalent to png_read_info(),
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1647followed the set of transformations indicated by the transform mask,
1648then png_read_image(), and finally png_read_end().
1649
1650(The final parameter of this call is not yet used. Someday it might point
1651to transformation parameters required by some future input transform.)
1652
1653You must use png_transforms and not call any png_set_transform() functions
1654when you use png_read_png().
1655
1656After you have called png_read_png(), you can retrieve the image data
1657with
1658
1659 row_pointers = png_get_rows(png_ptr, info_ptr);
1660
1661where row_pointers is an array of pointers to the pixel data for each row:
1662
1663 png_bytep row_pointers[height];
1664
1665If you know your image size and pixel size ahead of time, you can allocate
1666row_pointers prior to calling png_read_png() with
1667
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1668 if (height > PNG_UINT_32_MAX/(sizeof (png_byte)))
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1669 png_error (png_ptr,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1670 "Image is too tall to process in memory");
1671
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1672 if (width > PNG_UINT_32_MAX/pixel_size)
1673 png_error (png_ptr,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1674 "Image is too wide to process in memory");
1675
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1676 row_pointers = png_malloc(png_ptr,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1677 height*(sizeof (png_bytep)));
1678
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1679 for (int i=0; i<height, i++)
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]1680 row_pointers[i]=NULL; /* security precaution */
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1681
The Android Open Source Project4215dd12009-03-09 11:52:12 -0700[diff] [blame]1682 for (int i=0; i<height, i++)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1683 row_pointers[i]=png_malloc(png_ptr,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1684 width*pixel_size);
1685
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1686 png_set_rows(png_ptr, info_ptr, &row_pointers);
1687
1688Alternatively you could allocate your image in one big block and define
1689row_pointers[i] to point into the proper places in your block.
1690
1691If you use png_set_rows(), the application is responsible for freeing
1692row_pointers (and row_pointers[i], if they were separately allocated).
1693
1694If you don't allocate row_pointers ahead of time, png_read_png() will
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1695do it, and it'll be free'ed by libpng when you call png_destroy_*().
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1696
1697.SS The low-level read interface
1698
1699If you are going the low-level route, you are now ready to read all
1700the file information up to the actual image data. You do this with a
1701call to png_read_info().
1702
1703 png_read_info(png_ptr, info_ptr);
1704
1705This will process all chunks up to but not including the image data.
1706
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1707This also copies some of the data from the PNG file into the decode structure
1708for use in later transformations. Important information copied in is:
1709
17101) The PNG file gamma from the gAMA chunk. This overwrites the default value
1711provided by an earlier call to png_set_gamma or png_set_alpha_mode.
1712
17132) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
1714damages the information provided by an earlier call to png_set_background
1715resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
1716
17173) The number of significant bits in each component value. Libpng uses this to
1718optimize gamma handling by reducing the internal lookup table sizes.
1719
17204) The transparent color information from a tRNS chunk. This can be modified by
1721a later call to png_set_tRNS.
1722
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1723.SS Querying the info structure
1724
1725Functions are used to get the information from the info_ptr once it
1726has been read. Note that these fields may not be completely filled
1727in until png_read_end() has read the chunk data following the image.
1728
1729 png_get_IHDR(png_ptr, info_ptr, &width, &height,
1730 &bit_depth, &color_type, &interlace_type,
1731 &compression_type, &filter_method);
1732
1733 width - holds the width of the image
1734 in pixels (up to 2^31).
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1735
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1736 height - holds the height of the image
1737 in pixels (up to 2^31).
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1738
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1739 bit_depth - holds the bit depth of one of the
1740 image channels. (valid values are
1741 1, 2, 4, 8, 16 and depend also on
1742 the color_type. See also
1743 significant bits (sBIT) below).
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1744
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1745 color_type - describes which color/alpha channels
1746 are present.
1747 PNG_COLOR_TYPE_GRAY
1748 (bit depths 1, 2, 4, 8, 16)
1749 PNG_COLOR_TYPE_GRAY_ALPHA
1750 (bit depths 8, 16)
1751 PNG_COLOR_TYPE_PALETTE
1752 (bit depths 1, 2, 4, 8)
1753 PNG_COLOR_TYPE_RGB
1754 (bit_depths 8, 16)
1755 PNG_COLOR_TYPE_RGB_ALPHA
1756 (bit_depths 8, 16)
1757
1758 PNG_COLOR_MASK_PALETTE
1759 PNG_COLOR_MASK_COLOR
1760 PNG_COLOR_MASK_ALPHA
1761
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1762 interlace_type - (PNG_INTERLACE_NONE or
1763 PNG_INTERLACE_ADAM7)
1764
1765 compression_type - (must be PNG_COMPRESSION_TYPE_BASE
1766 for PNG 1.0)
1767
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1768 filter_method - (must be PNG_FILTER_TYPE_BASE
1769 for PNG 1.0, and can also be
1770 PNG_INTRAPIXEL_DIFFERENCING if
1771 the PNG datastream is embedded in
1772 a MNG-1.0 datastream)
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1773
1774 Any or all of interlace_type, compression_type, or
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1775 filter_method can be NULL if you are
1776 not interested in their values.
1777
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1778 Note that png_get_IHDR() returns 32-bit data into
1779 the application's width and height variables.
1780 This is an unsafe situation if these are 16-bit
1781 variables. In such situations, the
1782 png_get_image_width() and png_get_image_height()
1783 functions described below are safer.
1784
1785 width = png_get_image_width(png_ptr,
1786 info_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1787
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1788 height = png_get_image_height(png_ptr,
1789 info_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1790
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1791 bit_depth = png_get_bit_depth(png_ptr,
1792 info_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1793
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1794 color_type = png_get_color_type(png_ptr,
1795 info_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1796
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1797 interlace_type = png_get_interlace_type(png_ptr,
1798 info_ptr);
1799
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1800 compression_type = png_get_compression_type(png_ptr,
1801 info_ptr);
1802
1803 filter_method = png_get_filter_type(png_ptr,
1804 info_ptr);
1805
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1806 channels = png_get_channels(png_ptr, info_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1807
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1808 channels - number of channels of info for the
1809 color type (valid values are 1 (GRAY,
1810 PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
1811 4 (RGB_ALPHA or RGB + filler byte))
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1812
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1813 rowbytes = png_get_rowbytes(png_ptr, info_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1814
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1815 rowbytes - number of bytes needed to hold a row
1816
1817 signature = png_get_signature(png_ptr, info_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1818
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1819 signature - holds the signature read from the
1820 file (if any). The data is kept in
1821 the same offset it would be if the
1822 whole signature were read (i.e. if an
1823 application had already read in 4
1824 bytes of signature before starting
1825 libpng, the remaining 4 bytes would
1826 be in signature[4] through signature[7]
1827 (see png_set_sig_bytes())).
1828
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1829These are also important, but their validity depends on whether the chunk
1830has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
1831png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
1832data has been read, or zero if it is missing. The parameters to the
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1833png_get_<chunk> are set directly if they are simple data types, or a
1834pointer into the info_ptr is returned for any complex types.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1835
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1836The colorspace data from gAMA, cHRM, sRGB, iCCP, and sBIT chunks
1837is simply returned to give the application information about how the
1838image was encoded. Libpng itself only does transformations using the file
1839gamma when combining semitransparent pixels with the background color, and,
1840since libpng-1.6.0, when converting between 8-bit sRGB and 16-bit linear pixels
1841within the simplified API. Libpng also uses the file gamma when converting
1842RGB to gray, beginning with libpng-1.0.5, if the application calls
1843png_set_rgb_to_gray()).
1844
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1845 png_get_PLTE(png_ptr, info_ptr, &palette,
1846 &num_palette);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1847
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1848 palette - the palette for the file
1849 (array of png_color)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1850
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1851 num_palette - number of entries in the palette
1852
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1853 png_get_gAMA(png_ptr, info_ptr, &file_gamma);
1854 png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
1855
1856 file_gamma - the gamma at which the file is
1857 written (PNG_INFO_gAMA)
1858
1859 int_file_gamma - 100,000 times the gamma at which the
1860 file is written
1861
1862 png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x,
1863 &red_y, &green_x, &green_y, &blue_x, &blue_y)
1864 png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z,
1865 &green_X, &green_Y, &green_Z, &blue_X, &blue_Y,
1866 &blue_Z)
1867 png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x,
1868 &int_white_y, &int_red_x, &int_red_y,
1869 &int_green_x, &int_green_y, &int_blue_x,
1870 &int_blue_y)
1871 png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
1872 &int_red_Z, &int_green_X, &int_green_Y,
1873 &int_green_Z, &int_blue_X, &int_blue_Y,
1874 &int_blue_Z)
1875
1876 {white,red,green,blue}_{x,y}
1877 A color space encoding specified using the
1878 chromaticities of the end points and the
1879 white point. (PNG_INFO_cHRM)
1880
1881 {red,green,blue}_{X,Y,Z}
1882 A color space encoding specified using the
1883 encoding end points - the CIE tristimulus
1884 specification of the intended color of the red,
1885 green and blue channels in the PNG RGB data.
1886 The white point is simply the sum of the three
1887 end points. (PNG_INFO_cHRM)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1888
1889 png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1890
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]1891 srgb_intent - the rendering intent (PNG_INFO_sRGB)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1892 The presence of the sRGB chunk
1893 means that the pixel data is in the
1894 sRGB color space. This chunk also
1895 implies specific values of gAMA and
1896 cHRM.
1897
1898 png_get_iCCP(png_ptr, info_ptr, &name,
1899 &compression_type, &profile, &proflen);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1900
1901 name - The profile name.
1902
1903 compression_type - The compression type; always
1904 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
1905 You may give NULL to this argument to
1906 ignore it.
1907
1908 profile - International Color Consortium color
1909 profile data. May contain NULs.
1910
1911 proflen - length of profile data in bytes.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1912
1913 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1914
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1915 sig_bit - the number of significant bits for
1916 (PNG_INFO_sBIT) each of the gray,
1917 red, green, and blue channels,
1918 whichever are appropriate for the
1919 given color type (png_color_16)
1920
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1921 png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
1922 &num_trans, &trans_color);
1923
1924 trans_alpha - array of alpha (transparency)
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1925 entries for palette (PNG_INFO_tRNS)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1926
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1927 num_trans - number of transparent entries
1928 (PNG_INFO_tRNS)
1929
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1930 trans_color - graylevel or color sample values of
1931 the single transparent color for
1932 non-paletted images (PNG_INFO_tRNS)
1933
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1934 png_get_hIST(png_ptr, info_ptr, &hist);
1935 (PNG_INFO_hIST)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1936
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1937 hist - histogram of palette (array of
1938 png_uint_16)
1939
1940 png_get_tIME(png_ptr, info_ptr, &mod_time);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1941
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1942 mod_time - time image was last modified
1943 (PNG_VALID_tIME)
1944
1945 png_get_bKGD(png_ptr, info_ptr, &background);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1946
1947 background - background color (of type
1948 png_color_16p) (PNG_VALID_bKGD)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1949 valid 16-bit red, green and blue
1950 values, regardless of color_type
1951
1952 num_comments = png_get_text(png_ptr, info_ptr,
1953 &text_ptr, &num_text);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1954
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1955 num_comments - number of comments
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1956
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1957 text_ptr - array of png_text holding image
1958 comments
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1959
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1960 text_ptr[i].compression - type of compression used
1961 on "text" PNG_TEXT_COMPRESSION_NONE
1962 PNG_TEXT_COMPRESSION_zTXt
1963 PNG_ITXT_COMPRESSION_NONE
1964 PNG_ITXT_COMPRESSION_zTXt
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1965
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1966 text_ptr[i].key - keyword for comment. Must contain
1967 1-79 characters.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1968
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1969 text_ptr[i].text - text comments for current
1970 keyword. Can be empty.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1971
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1972 text_ptr[i].text_length - length of text string,
1973 after decompression, 0 for iTXt
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1974
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1975 text_ptr[i].itxt_length - length of itxt string,
1976 after decompression, 0 for tEXt/zTXt
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1977
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1978 text_ptr[i].lang - language of comment (empty
1979 string for unknown).
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1980
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1981 text_ptr[i].lang_key - keyword in UTF-8
1982 (empty string for unknown).
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1983
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1984 Note that the itxt_length, lang, and lang_key
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1985 members of the text_ptr structure only exist when the
1986 library is built with iTXt chunk support. Prior to
1987 libpng-1.4.0 the library was built by default without
1988 iTXt support. Also note that when iTXt is supported,
1989 they contain NULL pointers when the "compression"
1990 field contains PNG_TEXT_COMPRESSION_NONE or
1991 PNG_TEXT_COMPRESSION_zTXt.
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]1992
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1993 num_text - number of comments (same as
1994 num_comments; you can put NULL here
1995 to avoid the duplication)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]1996
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]1997 Note while png_set_text() will accept text, language,
1998 and translated keywords that can be NULL pointers, the
1999 structure returned by png_get_text will always contain
2000 regular zero-terminated C strings. They might be
2001 empty strings but they will never be NULL pointers.
2002
2003 num_spalettes = png_get_sPLT(png_ptr, info_ptr,
2004 &palette_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2005
2006 num_spalettes - number of sPLT chunks read.
2007
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2008 palette_ptr - array of palette structures holding
2009 contents of one or more sPLT chunks
2010 read.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2011
2012 png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
2013 &unit_type);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2014
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2015 offset_x - positive offset from the left edge
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2016 of the screen (can be negative)
2017
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2018 offset_y - positive offset from the top edge
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2019 of the screen (can be negative)
2020
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2021 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
2022
2023 png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
2024 &unit_type);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2025
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2026 res_x - pixels/unit physical resolution in
2027 x direction
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2028
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2029 res_y - pixels/unit physical resolution in
2030 x direction
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2031
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2032 unit_type - PNG_RESOLUTION_UNKNOWN,
2033 PNG_RESOLUTION_METER
2034
2035 png_get_sCAL(png_ptr, info_ptr, &unit, &width,
2036 &height)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2037
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2038 unit - physical scale units (an integer)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2039
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2040 width - width of a pixel in physical scale units
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2041
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2042 height - height of a pixel in physical scale units
2043 (width and height are doubles)
2044
2045 png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
2046 &height)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2047
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2048 unit - physical scale units (an integer)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2049
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2050 width - width of a pixel in physical scale units
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2051 (expressed as a string)
2052
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2053 height - height of a pixel in physical scale units
2054 (width and height are strings like "2.54")
2055
2056 num_unknown_chunks = png_get_unknown_chunks(png_ptr,
2057 info_ptr, &unknowns)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2058
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2059 unknowns - array of png_unknown_chunk
2060 structures holding unknown chunks
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2061
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2062 unknowns[i].name - name of unknown chunk
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2063
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2064 unknowns[i].data - data of unknown chunk
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2065
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2066 unknowns[i].size - size of unknown chunk's data
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2067
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2068 unknowns[i].location - position of chunk in file
2069
2070 The value of "i" corresponds to the order in which the
2071 chunks were read from the PNG file or inserted with the
2072 png_set_unknown_chunks() function.
2073
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2074 The value of "location" is a bitwise "or" of
2075
2076 PNG_HAVE_IHDR (0x01)
2077 PNG_HAVE_PLTE (0x02)
2078 PNG_AFTER_IDAT (0x08)
2079
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2080The data from the pHYs chunk can be retrieved in several convenient
2081forms:
2082
2083 res_x = png_get_x_pixels_per_meter(png_ptr,
2084 info_ptr)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2085
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2086 res_y = png_get_y_pixels_per_meter(png_ptr,
2087 info_ptr)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2088
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2089 res_x_and_y = png_get_pixels_per_meter(png_ptr,
2090 info_ptr)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2091
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2092 res_x = png_get_x_pixels_per_inch(png_ptr,
2093 info_ptr)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2094
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2095 res_y = png_get_y_pixels_per_inch(png_ptr,
2096 info_ptr)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2097
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2098 res_x_and_y = png_get_pixels_per_inch(png_ptr,
2099 info_ptr)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2100
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2101 aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
2102 info_ptr)
2103
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2104 Each of these returns 0 [signifying "unknown"] if
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2105 the data is not present or if res_x is 0;
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2106 res_x_and_y is 0 if res_x != res_y
2107
2108 Note that because of the way the resolutions are
2109 stored internally, the inch conversions won't
2110 come out to exactly even number. For example,
2111 72 dpi is stored as 0.28346 pixels/meter, and
2112 when this is retrieved it is 71.9988 dpi, so
2113 be sure to round the returned value appropriately
2114 if you want to display a reasonable-looking result.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2115
2116The data from the oFFs chunk can be retrieved in several convenient
2117forms:
2118
2119 x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2120
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2121 y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2122
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2123 x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2124
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2125 y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
2126
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2127 Each of these returns 0 [signifying "unknown" if both
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2128 x and y are 0] if the data is not present or if the
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2129 chunk is present but the unit is the pixel. The
2130 remark about inexact inch conversions applies here
2131 as well, because a value in inches can't always be
2132 converted to microns and back without some loss
2133 of precision.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2134
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2135For more information, see the
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2136PNG specification for chunk contents. Be careful with trusting
2137rowbytes, as some of the transformations could increase the space
2138needed to hold a row (expand, filler, gray_to_rgb, etc.).
2139See png_read_update_info(), below.
2140
2141A quick word about text_ptr and num_text. PNG stores comments in
2142keyword/text pairs, one pair per chunk, with no limit on the number
2143of text chunks, and a 2^31 byte limit on their size. While there are
2144suggested keywords, there is no requirement to restrict the use to these
2145strings. It is strongly suggested that keywords and text be sensible
2146to humans (that's the point), so don't use abbreviations. Non-printing
2147symbols are not allowed. See the PNG specification for more details.
2148There is also no requirement to have text after the keyword.
2149
2150Keywords should be limited to 79 Latin-1 characters without leading or
2151trailing spaces, but non-consecutive spaces are allowed within the
2152keyword. It is possible to have the same keyword any number of times.
2153The text_ptr is an array of png_text structures, each holding a
2154pointer to a language string, a pointer to a keyword and a pointer to
2155a text string. The text string, language code, and translated
2156keyword may be empty or NULL pointers. The keyword/text
2157pairs are put into the array in the order that they are received.
2158However, some or all of the text chunks may be after the image, so, to
2159make sure you have read all the text chunks, don't mess with these
2160until after you read the stuff after the image. This will be
2161mentioned again below in the discussion that goes with png_read_end().
2162
2163.SS Input transformations
2164
2165After you've read the header information, you can set up the library
2166to handle any special transformations of the image data. The various
2167ways to transform the data will be described in the order that they
2168should occur. This is important, as some of these change the color
2169type and/or bit depth of the data, and some others only work on
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2170certain color types and bit depths.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2171
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2172Transformations you request are ignored if they don't have any meaning for a
2173particular input data format. However some transformations can have an effect
2174as a result of a previous transformation. If you specify a contradictory set of
2175transformations, for example both adding and removing the alpha channel, you
2176cannot predict the final result.
2177
2178The color used for the transparency values should be supplied in the same
2179format/depth as the current image data. It is stored in the same format/depth
2180as the image data in a tRNS chunk, so this is what libpng expects for this data.
2181
2182The color used for the background value depends on the need_expand argument as
2183described below.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2184
2185Data will be decoded into the supplied row buffers packed into bytes
2186unless the library has been told to transform it into another format.
2187For example, 4 bit/pixel paletted or grayscale data will be returned
21882 pixels/byte with the leftmost pixel in the high-order bits of the
2189byte, unless png_set_packing() is called. 8-bit RGB data will be stored
2190in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
2191is called to insert filler bytes, either before or after each RGB triplet.
219216-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2193byte of the color value first, unless png_set_scale_16() is called to
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2194transform it to regular RGB RGB triplets, or png_set_filler() or
2195png_set_add alpha() is called to insert filler bytes, either before or
2196after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2197be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
2198or png_set_scale_16().
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2199
2200The following code transforms grayscale images of less than 8 to 8 bits,
2201changes paletted images to RGB, and adds a full alpha channel if there is
2202transparency information in a tRNS chunk. This is most useful on
2203grayscale images with bit depths of 2 or 4 or if there is a multiple-image
2204viewing application that wishes to treat all images in the same way.
2205
2206 if (color_type == PNG_COLOR_TYPE_PALETTE)
2207 png_set_palette_to_rgb(png_ptr);
2208
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2209 if (png_get_valid(png_ptr, info_ptr,
2210 PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
2211
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2212 if (color_type == PNG_COLOR_TYPE_GRAY &&
2213 bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
2214
2215The first two functions are actually aliases for png_set_expand(), added
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2216in libpng version 1.0.4, with the function names expanded to improve code
2217readability. In some future version they may actually do different
2218things.
2219
2220As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
2221added. It expands the sample depth without changing tRNS to alpha.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2222
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2223As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
2224png_set_expand(); however, the resultant channels have 16 bits rather than 8.
2225Use this when the output color or gray channels are made linear to avoid fairly
2226severe accuracy loss.
2227
2228 if (bit_depth < 16)
2229 png_set_expand_16(png_ptr);
2230
2231PNG can have files with 16 bits per channel. If you only can handle
22328 bits per channel, this will strip the pixels down to 8-bit.
2233
2234 if (bit_depth == 16)
2235#if PNG_LIBPNG_VER >= 10504
2236 png_set_scale_16(png_ptr);
2237#else
2238 png_set_strip_16(png_ptr);
2239#endif
2240
2241(The more accurate "png_set_scale_16()" API became available in libpng version
22421.5.4).
2243
2244If you need to process the alpha channel on the image separately from the image
2245data (for example if you convert it to a bitmap mask) it is possible to have
2246libpng strip the channel leaving just RGB or gray data:
2247
2248 if (color_type & PNG_COLOR_MASK_ALPHA)
2249 png_set_strip_alpha(png_ptr);
2250
2251If you strip the alpha channel you need to find some other way of dealing with
2252the information. If, instead, you want to convert the image to an opaque
2253version with no alpha channel use png_set_background; see below.
2254
2255As of libpng version 1.5.2, almost all useful expansions are supported, the
2256major ommissions are conversion of grayscale to indexed images (which can be
2257done trivially in the application) and conversion of indexed to grayscale (which
2258can be done by a trivial manipulation of the palette.)
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2259
2260In the following table, the 01 means grayscale with depth<8, 31 means
2261indexed with depth<8, other numerals represent the color type, "T" means
2262the tRNS chunk is present, A means an alpha channel is present, and O
2263means tRNS or alpha is present but all pixels in the image are opaque.
2264
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2265 FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2266 TO
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2267 01 - [G] - - - - - - - - - - - - -
2268 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
2269 0 1 G + . . G G G G G G B B GB GB
2270 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
2271 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
2272 2 C P C C C + . . C - - CB CB B B
2273 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
2274 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
2275 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
2276 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
2277 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
2278 4A lA G A T T GA GT GT GA GT GT + BA G GBA
2279 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
2280 6A CA PA CA C C A T tT PA P P C CBA + BA
2281 6O CA PBA CA C C A tT T PA P P CBA C BA +
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2282
2283Within the matrix,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2284 "+" identifies entries where 'from' and 'to' are the same.
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2285 "-" means the transformation is not supported.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2286 "." means nothing is necessary (a tRNS chunk can just be ignored).
2287 "t" means the transformation is obtained by png_set_tRNS.
2288 "A" means the transformation is obtained by png_set_add_alpha().
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2289 "X" means the transformation is obtained by png_set_expand().
2290 "1" means the transformation is obtained by
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2291 png_set_expand_gray_1_2_4_to_8() (and by png_set_expand()
2292 if there is no transparency in the original or the final
2293 format).
2294 "C" means the transformation is obtained by png_set_gray_to_rgb().
2295 "G" means the transformation is obtained by png_set_rgb_to_gray().
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2296 "P" means the transformation is obtained by
2297 png_set_expand_palette_to_rgb().
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2298 "p" means the transformation is obtained by png_set_packing().
2299 "Q" means the transformation is obtained by png_set_quantize().
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2300 "T" means the transformation is obtained by
2301 png_set_tRNS_to_alpha().
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2302 "B" means the transformation is obtained by
2303 png_set_background(), or png_strip_alpha().
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2304
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2305When an entry has multiple transforms listed all are required to cause the
2306right overall transformation. When two transforms are separated by a comma
2307either will do the job. When transforms are enclosed in [] the transform should
2308do the job but this is currently unimplemented - a different format will result
2309if the suggested transformations are used.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2310
2311In PNG files, the alpha channel in an image
2312is the level of opacity. If you need the alpha channel in an image to
2313be the level of transparency instead of opacity, you can invert the
2314alpha channel (or the tRNS chunk data) after it's read, so that 0 is
2315fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
2316images) is fully transparent, with
2317
2318 png_set_invert_alpha(png_ptr);
2319
2320PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
2321they can, resulting in, for example, 8 pixels per byte for 1 bit
2322files. This code expands to 1 pixel per byte without changing the
2323values of the pixels:
2324
2325 if (bit_depth < 8)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2326 png_set_packing(png_ptr);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2327
2328PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
2329stored in a PNG image have been "scaled" or "shifted" up to the next
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2330higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
2331to 8 bits/sample in the range [0, 255]). However, it is also possible
2332to convert the PNG pixel data back to the original bit depth of the
2333image. This call reduces the pixels back down to the original bit depth:
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2334
2335 png_color_8p sig_bit;
2336
2337 if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2338 png_set_shift(png_ptr, sig_bit);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2339
2340PNG files store 3-color pixels in red, green, blue order. This code
2341changes the storage of the pixels to blue, green, red:
2342
2343 if (color_type == PNG_COLOR_TYPE_RGB ||
2344 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2345 png_set_bgr(png_ptr);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2346
2347PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
2348into 4 or 8 bytes for windowing systems that need them in this format:
2349
2350 if (color_type == PNG_COLOR_TYPE_RGB)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2351 png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2352
2353where "filler" is the 8 or 16-bit number to fill with, and the location is
2354either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
2355you want the filler before the RGB or after. This transformation
2356does not affect images that already have full alpha channels. To add an
2357opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
2358will generate RGBA pixels.
2359
2360Note that png_set_filler() does not change the color type. If you want
2361to do that, you can add a true alpha channel with
2362
2363 if (color_type == PNG_COLOR_TYPE_RGB ||
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2364 color_type == PNG_COLOR_TYPE_GRAY)
2365 png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2366
2367where "filler" contains the alpha value to assign to each pixel.
2368This function was added in libpng-1.2.7.
2369
2370If you are reading an image with an alpha channel, and you need the
2371data as ARGB instead of the normal PNG format RGBA:
2372
2373 if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2374 png_set_swap_alpha(png_ptr);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2375
2376For some uses, you may want a grayscale image to be represented as
2377RGB. This code will do that conversion:
2378
2379 if (color_type == PNG_COLOR_TYPE_GRAY ||
2380 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2381 png_set_gray_to_rgb(png_ptr);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2382
2383Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
2384with alpha.
2385
2386 if (color_type == PNG_COLOR_TYPE_RGB ||
2387 color_type == PNG_COLOR_TYPE_RGB_ALPHA)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2388 png_set_rgb_to_gray(png_ptr, error_action,
2389 double red_weight, double green_weight);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2390
2391 error_action = 1: silently do the conversion
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2392
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2393 error_action = 2: issue a warning if the original
2394 image has any pixel where
2395 red != green or red != blue
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2396
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2397 error_action = 3: issue an error and abort the
2398 conversion if the original
2399 image has any pixel where
2400 red != green or red != blue
2401
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2402 red_weight: weight of red component
2403
2404 green_weight: weight of green component
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2405 If either weight is negative, default
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2406 weights are used.
2407
2408In the corresponding fixed point API the red_weight and green_weight values are
2409simply scaled by 100,000:
2410
2411 png_set_rgb_to_gray(png_ptr, error_action,
2412 png_fixed_point red_weight,
2413 png_fixed_point green_weight);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2414
2415If you have set error_action = 1 or 2, you can
2416later check whether the image really was gray, after processing
2417the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
2418It will return a png_byte that is zero if the image was gray or
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]24191 if there were any non-gray pixels. Background and sBIT data
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2420will be silently converted to grayscale, using the green channel
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2421data for sBIT, regardless of the error_action setting.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2422
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2423The default values come from the PNG file cHRM chunk if present; otherwise, the
2424defaults correspond to the ITU-R recommendation 709, and also the sRGB color
2425space, as recommended in the Charles Poynton's Colour FAQ,
2426<http://www.poynton.com/>, in section 9:
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2427
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2428 <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2429
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2430 Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
2431
2432Previous versions of this document, 1998 through 2002, recommended a slightly
2433different formula:
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2434
2435 Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
2436
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2437Libpng uses an integer approximation:
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2438
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2439 Y = (6968 * R + 23434 * G + 2366 * B)/32768
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2440
2441The calculation is done in a linear colorspace, if the image gamma
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2442can be determined.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2443
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2444The png_set_background() function has been described already; it tells libpng to
2445composite images with alpha or simple transparency against the supplied
2446background color. For compatibility with versions of libpng earlier than
2447libpng-1.5.4 it is recommended that you call the function after reading the file
2448header, even if you don't want to use the color in a bKGD chunk, if one exists.
2449
2450If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
2451you may use this color, or supply another color more suitable for
2452the current display (e.g., the background color from a web page). You
2453need to tell libpng how the color is represented, both the format of the
2454component values in the color (the number of bits) and the gamma encoding of the
2455color. The function takes two arguments, background_gamma_mode and need_expand
2456to convey this information; however, only two combinations are likely to be
2457useful:
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2458
2459 png_color_16 my_background;
2460 png_color_16p image_background;
2461
2462 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2463 png_set_background(png_ptr, image_background,
2464 PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2465 else
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2466 png_set_background(png_ptr, &my_background,
2467 PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2468
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2469The second call was described above - my_background is in the format of the
2470final, display, output produced by libpng. Because you now know the format of
2471the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
2472output and to retain palette images (the palette colors will be modified
2473appropriately and the tRNS chunk removed.) However, if you are doing this,
2474take great care not to ask for transformations without checking first that
2475they apply!
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2476
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2477In the first call the background color has the original bit depth and color type
2478of the PNG file. So, for palette images the color is supplied as a palette
2479index and for low bit greyscale images the color is a reduced bit value in
2480image_background->gray.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2481
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2482If you didn't call png_set_gamma() before reading the file header, for example
2483if you need your code to remain compatible with older versions of libpng prior
2484to libpng-1.5.4, this is the place to call it.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2485
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2486Do not call it if you called png_set_alpha_mode(); doing so will damage the
2487settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
2488supported then you can certainly do png_set_gamma() before reading the PNG
2489header.)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2490
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2491This API unconditionally sets the screen and file gamma values, so it will
2492override the value in the PNG file unless it is called before the PNG file
2493reading starts. For this reason you must always call it with the PNG file
2494value when you call it in this position:
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2495
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2496 if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
2497 png_set_gamma(png_ptr, screen_gamma, file_gamma);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2498
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2499 else
2500 png_set_gamma(png_ptr, screen_gamma, 0.45455);
2501
2502If you need to reduce an RGB file to a paletted file, or if a paletted
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2503file has more entries then will fit on your screen, png_set_quantize()
2504will do that. Note that this is a simple match quantization that merely
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2505finds the closest color available. This should work fairly well with
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2506optimized palettes, but fairly badly with linear color cubes. If you
2507pass a palette that is larger than maximum_colors, the file will
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2508reduce the number of colors in the palette so it will fit into
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2509maximum_colors. If there is a histogram, libpng will use it to make
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2510more intelligent choices when reducing the palette. If there is no
2511histogram, it may not do as good a job.
2512
2513 if (color_type & PNG_COLOR_MASK_COLOR)
2514 {
2515 if (png_get_valid(png_ptr, info_ptr,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2516 PNG_INFO_PLTE))
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2517 {
2518 png_uint_16p histogram = NULL;
2519
2520 png_get_hIST(png_ptr, info_ptr,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2521 &histogram);
2522 png_set_quantize(png_ptr, palette, num_palette,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2523 max_screen_colors, histogram, 1);
2524 }
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2525
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2526 else
2527 {
2528 png_color std_color_cube[MAX_SCREEN_COLORS] =
2529 { ... colors ... };
2530
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2531 png_set_quantize(png_ptr, std_color_cube,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2532 MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
2533 NULL,0);
2534 }
2535 }
2536
2537PNG files describe monochrome as black being zero and white being one.
2538The following code will reverse this (make black be one and white be
2539zero):
2540
2541 if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
2542 png_set_invert_mono(png_ptr);
2543
2544This function can also be used to invert grayscale and gray-alpha images:
2545
2546 if (color_type == PNG_COLOR_TYPE_GRAY ||
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2547 color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2548 png_set_invert_mono(png_ptr);
2549
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2550PNG files store 16-bit pixels in network byte order (big-endian,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2551ie. most significant bits first). This code changes the storage to the
2552other way (little-endian, i.e. least significant bits first, the
2553way PCs store them):
2554
2555 if (bit_depth == 16)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2556 png_set_swap(png_ptr);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2557
2558If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
2559need to change the order the pixels are packed into bytes, you can use:
2560
2561 if (bit_depth < 8)
2562 png_set_packswap(png_ptr);
2563
2564Finally, you can write your own transformation function if none of
2565the existing ones meets your needs. This is done by setting a callback
2566with
2567
2568 png_set_read_user_transform_fn(png_ptr,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2569 read_transform_fn);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2570
2571You must supply the function
2572
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2573 void read_transform_fn(png_structp png_ptr, png_row_infop
2574 row_info, png_bytep data)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2575
2576See pngtest.c for a working example. Your function will be called
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2577after all of the other transformations have been processed. Take care with
2578interlaced images if you do the interlace yourself - the width of the row is the
2579width in 'row_info', not the overall image width.
2580
2581If supported, libpng provides two information routines that you can use to find
2582where you are in processing the image:
2583
2584 png_get_current_pass_number(png_structp png_ptr);
2585 png_get_current_row_number(png_structp png_ptr);
2586
2587Don't try using these outside a transform callback - firstly they are only
2588supported if user transforms are supported, secondly they may well return
2589unexpected results unless the row is actually being processed at the moment they
2590are called.
2591
2592With interlaced
2593images the value returned is the row in the input sub-image image. Use
2594PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
2595find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
2596
2597The discussion of interlace handling above contains more information on how to
2598use these values.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2599
2600You can also set up a pointer to a user structure for use by your
2601callback function, and you can inform libpng that your transform
2602function will change the number of channels or bit depth with the
2603function
2604
2605 png_set_user_transform_info(png_ptr, user_ptr,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2606 user_depth, user_channels);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2607
2608The user's application, not libpng, is responsible for allocating and
2609freeing any memory required for the user structure.
2610
2611You can retrieve the pointer via the function
2612png_get_user_transform_ptr(). For example:
2613
2614 voidp read_user_transform_ptr =
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2615 png_get_user_transform_ptr(png_ptr);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2616
2617The last thing to handle is interlacing; this is covered in detail below,
2618but you must call the function here if you want libpng to handle expansion
2619of the interlaced image.
2620
2621 number_of_passes = png_set_interlace_handling(png_ptr);
2622
2623After setting the transformations, libpng can update your png_info
2624structure to reflect any transformations you've requested with this
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2625call.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2626
2627 png_read_update_info(png_ptr, info_ptr);
2628
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2629This is most useful to update the info structure's rowbytes
2630field so you can use it to allocate your image memory. This function
2631will also update your palette with the correct screen_gamma and
2632background if these have been given with the calls above. You may
2633only call png_read_update_info() once with a particular info_ptr.
2634
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2635After you call png_read_update_info(), you can allocate any
2636memory you need to hold the image. The row data is simply
2637raw byte data for all forms of images. As the actual allocation
2638varies among applications, no example will be given. If you
2639are allocating one large chunk, you will need to build an
2640array of pointers to each row, as it will be needed for some
2641of the functions below.
2642
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2643Remember: Before you call png_read_update_info(), the png_get_*()
2644functions return the values corresponding to the original PNG image.
2645After you call png_read_update_info the values refer to the image
2646that libpng will output. Consequently you must call all the png_set_
2647functions before you call png_read_update_info(). This is particularly
2648important for png_set_interlace_handling() - if you are going to call
2649png_read_update_info() you must call png_set_interlace_handling() before
2650it unless you want to receive interlaced output.
2651
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2652.SS Reading image data
2653
2654After you've allocated memory, you can read the image data.
2655The simplest way to do this is in one function call. If you are
2656allocating enough memory to hold the whole image, you can just
2657call png_read_image() and libpng will read in all the image data
2658and put it in the memory area supplied. You will need to pass in
2659an array of pointers to each row.
2660
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2661This function automatically handles interlacing, so you don't
2662need to call png_set_interlace_handling() (unless you call
2663png_read_update_info()) or call this function multiple times, or any
2664of that other stuff necessary with png_read_rows().
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2665
2666 png_read_image(png_ptr, row_pointers);
2667
2668where row_pointers is:
2669
2670 png_bytep row_pointers[height];
2671
2672You can point to void or char or whatever you use for pixels.
2673
2674If you don't want to read in the whole image at once, you can
2675use png_read_rows() instead. If there is no interlacing (check
2676interlace_type == PNG_INTERLACE_NONE), this is simple:
2677
2678 png_read_rows(png_ptr, row_pointers, NULL,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2679 number_of_rows);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2680
2681where row_pointers is the same as in the png_read_image() call.
2682
2683If you are doing this just one row at a time, you can do this with
2684a single row_pointer instead of an array of row_pointers:
2685
2686 png_bytep row_pointer = row;
2687 png_read_row(png_ptr, row_pointer, NULL);
2688
2689If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
2690get somewhat harder. The only current (PNG Specification version 1.2)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2691interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
2692a somewhat complicated 2D interlace scheme, known as Adam7, that
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2693breaks down an image into seven smaller images of varying size, based
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2694on an 8x8 grid. This number is defined (from libpng 1.5) as
2695PNG_INTERLACE_ADAM7_PASSES in png.h
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2696
2697libpng can fill out those images or it can give them to you "as is".
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2698It is almost always better to have libpng handle the interlacing for you.
2699If you want the images filled out, there are two ways to do that. The one
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2700mentioned in the PNG specification is to expand each pixel to cover
2701those pixels that have not been read yet (the "rectangle" method).
2702This results in a blocky image for the first pass, which gradually
2703smooths out as more pixels are read. The other method is the "sparkle"
2704method, where pixels are drawn only in their final locations, with the
2705rest of the image remaining whatever colors they were initialized to
2706before the start of the read. The first method usually looks better,
2707but tends to be slower, as there are more pixels to put in the rows.
2708
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2709If, as is likely, you want libpng to expand the images, call this before
2710calling png_start_read_image() or png_read_update_info():
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2711
2712 if (interlace_type == PNG_INTERLACE_ADAM7)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2713 number_of_passes
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2714 = png_set_interlace_handling(png_ptr);
2715
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2716This will return the number of passes needed. Currently, this is seven,
2717but may change if another interlace type is added. This function can be
2718called even if the file is not interlaced, where it will return one pass.
2719You then need to read the whole image 'number_of_passes' times. Each time
2720will distribute the pixels from the current pass to the correct place in
2721the output image, so you need to supply the same rows to png_read_rows in
2722each pass.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2723
2724If you are not going to display the image after each pass, but are
2725going to wait until the entire image is read in, use the sparkle
2726effect. This effect is faster and the end result of either method
2727is exactly the same. If you are planning on displaying the image
2728after each pass, the "rectangle" effect is generally considered the
2729better looking one.
2730
2731If you only want the "sparkle" effect, just call png_read_rows() as
2732normal, with the third parameter NULL. Make sure you make pass over
2733the image number_of_passes times, and you don't change the data in the
2734rows between calls. You can change the locations of the data, just
2735not the data. Each pass only writes the pixels appropriate for that
2736pass, and assumes the data from previous passes is still valid.
2737
2738 png_read_rows(png_ptr, row_pointers, NULL,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2739 number_of_rows);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2740
2741If you only want the first effect (the rectangles), do the same as
2742before except pass the row buffer in the third parameter, and leave
2743the second parameter NULL.
2744
2745 png_read_rows(png_ptr, NULL, row_pointers,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2746 number_of_rows);
2747
2748If you don't want libpng to handle the interlacing details, just call
2749png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
2750Each of the images is a valid image by itself; however, you will almost
2751certainly need to distribute the pixels from each sub-image to the
2752correct place. This is where everything gets very tricky.
2753
2754If you want to retrieve the separate images you must pass the correct
2755number of rows to each successive call of png_read_rows(). The calculation
2756gets pretty complicated for small images, where some sub-images may
2757not even exist because either their width or height ends up zero.
2758libpng provides two macros to help you in 1.5 and later versions:
2759
2760 png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
2761 png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
2762
2763Respectively these tell you the width and height of the sub-image
2764corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
2765this can be confusing because the specification refers to the same passes
2766as 1 to 7! Be careful, you must check both the width and height before
2767calling png_read_rows() and not call it for that pass if either is zero.
2768
2769You can, of course, read each sub-image row by row. If you want to
2770produce optimal code to make a pixel-by-pixel transformation of an
2771interlaced image this is the best approach; read each row of each pass,
2772transform it, and write it out to a new interlaced image.
2773
2774If you want to de-interlace the image yourself libpng provides further
2775macros to help that tell you where to place the pixels in the output image.
2776Because the interlacing scheme is rectangular - sub-image pixels are always
2777arranged on a rectangular grid - all you need to know for each pass is the
2778starting column and row in the output image of the first pixel plus the
2779spacing between each pixel. As of libpng 1.5 there are four macros to
2780retrieve this information:
2781
2782 png_uint_32 x = PNG_PASS_START_COL(pass);
2783 png_uint_32 y = PNG_PASS_START_ROW(pass);
2784 png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
2785 png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
2786
2787These allow you to write the obvious loop:
2788
2789 png_uint_32 input_y = 0;
2790 png_uint_32 output_y = PNG_PASS_START_ROW(pass);
2791
2792 while (output_y < output_image_height)
2793 {
2794 png_uint_32 input_x = 0;
2795 png_uint_32 output_x = PNG_PASS_START_COL(pass);
2796
2797 while (output_x < output_image_width)
2798 {
2799 image[output_y][output_x] =
2800 subimage[pass][input_y][input_x++];
2801
2802 output_x += xStep;
2803 }
2804
2805 ++input_y;
2806 output_y += yStep;
2807 }
2808
2809Notice that the steps between successive output rows and columns are
2810returned as shifts. This is possible because the pixels in the subimages
2811are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
2812image. In practice you may need to directly calculate the output coordinate
2813given an input coordinate. libpng provides two further macros for this
2814purpose:
2815
2816 png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
2817 png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
2818
2819Finally a pair of macros are provided to tell you if a particular image
2820row or column appears in a given pass:
2821
2822 int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
2823 int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
2824
2825Bear in mind that you will probably also need to check the width and height
2826of the pass in addition to the above to be sure the pass even exists!
2827
2828With any luck you are convinced by now that you don't want to do your own
2829interlace handling. In reality normally the only good reason for doing this
2830is if you are processing PNG files on a pixel-by-pixel basis and don't want
2831to load the whole file into memory when it is interlaced.
2832
2833libpng includes a test program, pngvalid, that illustrates reading and
2834writing of interlaced images. If you can't get interlacing to work in your
2835code and don't want to leave it to libpng (the recommended approach), see
2836how pngvalid.c does it.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2837
2838.SS Finishing a sequential read
2839
2840After you are finished reading the image through the
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]2841low-level interface, you can finish reading the file.
2842
2843If you want to use a different crc action for handling CRC errors in
2844chunks after the image data, you can call png_set_crc_action()
2845again at this point.
2846
2847If you are interested in comments or time, which may be stored either
2848before or after the image data, you should pass the separate png_info
2849struct if you want to keep the comments from before and after the image
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2850separate.
2851
2852 png_infop end_info = png_create_info_struct(png_ptr);
2853
2854 if (!end_info)
2855 {
2856 png_destroy_read_struct(&png_ptr, &info_ptr,
2857 (png_infopp)NULL);
2858 return (ERROR);
2859 }
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2860
2861 png_read_end(png_ptr, end_info);
2862
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2863If you are not interested, you should still call png_read_end()
2864but you can pass NULL, avoiding the need to create an end_info structure.
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]2865If you do this, libpng will not process any chunks after IDAT other than
2866skipping over them and perhaps (depending on whether you have called
2867png_set_crc_action) checking their CRCs while looking for the IEND chunk.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2868
2869 png_read_end(png_ptr, (png_infop)NULL);
2870
2871If you don't call png_read_end(), then your file pointer will be
2872left pointing to the first chunk after the last IDAT, which is probably
2873not what you want if you expect to read something beyond the end of
2874the PNG datastream.
2875
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2876When you are done, you can free all memory allocated by libpng like this:
2877
2878 png_destroy_read_struct(&png_ptr, &info_ptr,
2879 &end_info);
2880
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2881or, if you didn't create an end_info structure,
2882
2883 png_destroy_read_struct(&png_ptr, &info_ptr,
2884 (png_infopp)NULL);
2885
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2886It is also possible to individually free the info_ptr members that
2887point to libpng-allocated storage with the following function:
2888
2889 png_free_data(png_ptr, info_ptr, mask, seq)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2890
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2891 mask - identifies data to be freed, a mask
2892 containing the bitwise OR of one or
2893 more of
2894 PNG_FREE_PLTE, PNG_FREE_TRNS,
2895 PNG_FREE_HIST, PNG_FREE_ICCP,
2896 PNG_FREE_PCAL, PNG_FREE_ROWS,
2897 PNG_FREE_SCAL, PNG_FREE_SPLT,
2898 PNG_FREE_TEXT, PNG_FREE_UNKN,
2899 or simply PNG_FREE_ALL
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2900
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2901 seq - sequence number of item to be freed
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]2902 (\-1 for all items)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2903
2904This function may be safely called when the relevant storage has
2905already been freed, or has not yet been allocated, or was allocated
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2906by the user and not by libpng, and will in those cases do nothing.
2907The "seq" parameter is ignored if only one item of the selected data
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]2908type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2909are allowed for the data type identified in the mask, such as text or
2910sPLT, only the n'th item in the structure is freed, where n is "seq".
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2911
2912The default behavior is only to free data that was allocated internally
2913by libpng. This can be changed, so that libpng will not free the data,
2914or so that it will free data that was allocated by the user with png_malloc()
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2915or png_calloc() and passed in via a png_set_*() function, with
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2916
2917 png_data_freer(png_ptr, info_ptr, freer, mask)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2918
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2919 freer - one of
2920 PNG_DESTROY_WILL_FREE_DATA
2921 PNG_SET_WILL_FREE_DATA
2922 PNG_USER_WILL_FREE_DATA
2923
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2924 mask - which data elements are affected
2925 same choices as in png_free_data()
2926
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2927This function only affects data that has already been allocated.
2928You can call this function after reading the PNG data but before calling
2929any png_set_*() functions, to control whether the user or the png_set_*()
2930function is responsible for freeing any existing data that might be present,
2931and again after the png_set_*() functions to control whether the user
2932or png_destroy_*() is supposed to free the data. When the user assumes
2933responsibility for libpng-allocated data, the application must use
2934png_free() to free it, and when the user transfers responsibility to libpng
2935for data that the user has allocated, the user must have used png_malloc()
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2936or png_calloc() to allocate it.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2937
2938If you allocated your row_pointers in a single block, as suggested above in
2939the description of the high level read interface, you must not transfer
2940responsibility for freeing it to the png_set_rows or png_read_destroy function,
2941because they would also try to free the individual row_pointers[i].
2942
2943If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
2944separately, do not transfer responsibility for freeing text_ptr to libpng,
2945because when libpng fills a png_text structure it combines these members with
2946the key member, and png_free_data() will free only text_ptr.key. Similarly,
2947if you transfer responsibility for free'ing text_ptr from libpng to your
2948application, your application must not separately free those members.
2949
2950The png_free_data() function will turn off the "valid" flag for anything
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]2951it frees. If you need to turn the flag off for a chunk that was freed by
2952your application instead of by libpng, you can use
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2953
2954 png_set_invalid(png_ptr, info_ptr, mask);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2955
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2956 mask - identifies the chunks to be made invalid,
2957 containing the bitwise OR of one or
2958 more of
2959 PNG_INFO_gAMA, PNG_INFO_sBIT,
2960 PNG_INFO_cHRM, PNG_INFO_PLTE,
2961 PNG_INFO_tRNS, PNG_INFO_bKGD,
2962 PNG_INFO_hIST, PNG_INFO_pHYs,
2963 PNG_INFO_oFFs, PNG_INFO_tIME,
2964 PNG_INFO_pCAL, PNG_INFO_sRGB,
2965 PNG_INFO_iCCP, PNG_INFO_sPLT,
2966 PNG_INFO_sCAL, PNG_INFO_IDAT
2967
2968For a more compact example of reading a PNG image, see the file example.c.
2969
2970.SS Reading PNG files progressively
2971
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2972The progressive reader is slightly different from the non-progressive
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2973reader. Instead of calling png_read_info(), png_read_rows(), and
2974png_read_end(), you make one call to png_process_data(), which calls
2975callbacks when it has the info, a row, or the end of the image. You
2976set up these callbacks with png_set_progressive_read_fn(). You don't
2977have to worry about the input/output functions of libpng, as you are
2978giving the library the data directly in png_process_data(). I will
2979assume that you have read the section on reading PNG files above,
2980so I will only highlight the differences (although I will show
2981all of the code).
2982
2983png_structp png_ptr;
2984png_infop info_ptr;
2985
2986 /* An example code fragment of how you would
2987 initialize the progressive reader in your
2988 application. */
2989 int
2990 initialize_png_reader()
2991 {
2992 png_ptr = png_create_read_struct
2993 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
2994 user_error_fn, user_warning_fn);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2995
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2996 if (!png_ptr)
2997 return (ERROR);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]2998
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]2999 info_ptr = png_create_info_struct(png_ptr);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3000
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3001 if (!info_ptr)
3002 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3003 png_destroy_read_struct(&png_ptr,
3004 (png_infopp)NULL, (png_infopp)NULL);
3005 return (ERROR);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3006 }
3007
3008 if (setjmp(png_jmpbuf(png_ptr)))
3009 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3010 png_destroy_read_struct(&png_ptr, &info_ptr,
3011 (png_infopp)NULL);
3012 return (ERROR);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3013 }
3014
3015 /* This one's new. You can provide functions
3016 to be called when the header info is valid,
3017 when each row is completed, and when the image
3018 is finished. If you aren't using all functions,
3019 you can specify NULL parameters. Even when all
3020 three functions are NULL, you need to call
3021 png_set_progressive_read_fn(). You can use
3022 any struct as the user_ptr (cast to a void pointer
3023 for the function call), and retrieve the pointer
3024 from inside the callbacks using the function
3025
3026 png_get_progressive_ptr(png_ptr);
3027
3028 which will return a void pointer, which you have
3029 to cast appropriately.
3030 */
3031 png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
3032 info_callback, row_callback, end_callback);
3033
3034 return 0;
3035 }
3036
3037 /* A code fragment that you call as you receive blocks
3038 of data */
3039 int
3040 process_data(png_bytep buffer, png_uint_32 length)
3041 {
3042 if (setjmp(png_jmpbuf(png_ptr)))
3043 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3044 png_destroy_read_struct(&png_ptr, &info_ptr,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3045 (png_infopp)NULL);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3046 return (ERROR);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3047 }
3048
3049 /* This one's new also. Simply give it a chunk
3050 of data from the file stream (in order, of
3051 course). On machines with segmented memory
3052 models machines, don't give it any more than
3053 64K. The library seems to run fine with sizes
3054 of 4K. Although you can give it much less if
3055 necessary (I assume you can give it chunks of
3056 1 byte, I haven't tried less then 256 bytes
3057 yet). When this function returns, you may
3058 want to display any rows that were generated
3059 in the row callback if you don't already do
3060 so there.
3061 */
3062 png_process_data(png_ptr, info_ptr, buffer, length);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3063
3064 /* At this point you can call png_process_data_skip if
3065 you want to handle data the library will skip yourself;
3066 it simply returns the number of bytes to skip (and stops
3067 libpng skipping that number of bytes on the next
3068 png_process_data call).
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3069 return 0;
3070 }
3071
3072 /* This function is called (as set by
3073 png_set_progressive_read_fn() above) when enough data
3074 has been supplied so all of the header has been
3075 read.
3076 */
3077 void
3078 info_callback(png_structp png_ptr, png_infop info)
3079 {
3080 /* Do any setup here, including setting any of
3081 the transformations mentioned in the Reading
3082 PNG files section. For now, you _must_ call
3083 either png_start_read_image() or
3084 png_read_update_info() after all the
3085 transformations are set (even if you don't set
3086 any). You may start getting rows before
3087 png_process_data() returns, so this is your
3088 last chance to prepare for that.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3089
3090 This is where you turn on interlace handling,
3091 assuming you don't want to do it yourself.
3092
3093 If you need to you can stop the processing of
3094 your original input data at this point by calling
3095 png_process_data_pause. This returns the number
3096 of unprocessed bytes from the last png_process_data
3097 call - it is up to you to ensure that the next call
3098 sees these bytes again. If you don't want to bother
3099 with this you can get libpng to cache the unread
3100 bytes by setting the 'save' parameter (see png.h) but
3101 then libpng will have to copy the data internally.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3102 */
3103 }
3104
3105 /* This function is called when each row of image
3106 data is complete */
3107 void
3108 row_callback(png_structp png_ptr, png_bytep new_row,
3109 png_uint_32 row_num, int pass)
3110 {
3111 /* If the image is interlaced, and you turned
3112 on the interlace handler, this function will
3113 be called for every row in every pass. Some
3114 of these rows will not be changed from the
3115 previous pass. When the row is not changed,
3116 the new_row variable will be NULL. The rows
3117 and passes are called in order, so you don't
3118 really need the row_num and pass, but I'm
3119 supplying them because it may make your life
3120 easier.
3121
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3122 If you did not turn on interlace handling then
3123 the callback is called for each row of each
3124 sub-image when the image is interlaced. In this
3125 case 'row_num' is the row in the sub-image, not
3126 the row in the output image as it is in all other
3127 cases.
3128
3129 For the non-NULL rows of interlaced images when
3130 you have switched on libpng interlace handling,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3131 you must call png_progressive_combine_row()
3132 passing in the row and the old row. You can
3133 call this function for NULL rows (it will just
3134 return) and for non-interlaced images (it just
3135 does the memcpy for you) if it will make the
3136 code easier. Thus, you can just do this for
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3137 all cases if you switch on interlace handling;
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3138 */
3139
3140 png_progressive_combine_row(png_ptr, old_row,
3141 new_row);
3142
3143 /* where old_row is what was displayed for
3144 previously for the row. Note that the first
3145 pass (pass == 0, really) will completely cover
3146 the old row, so the rows do not have to be
3147 initialized. After the first pass (and only
3148 for interlaced images), you will have to pass
3149 the current row, and the function will combine
3150 the old row and the new row.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3151
3152 You can also call png_process_data_pause in this
3153 callback - see above.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3154 */
3155 }
3156
3157 void
3158 end_callback(png_structp png_ptr, png_infop info)
3159 {
3160 /* This function is called after the whole image
3161 has been read, including any chunks after the
3162 image (up to and including the IEND). You
3163 will usually have the same info chunk as you
3164 had in the header, although some data may have
3165 been added to the comments and time fields.
3166
3167 Most people won't do much here, perhaps setting
3168 a flag that marks the image as finished.
3169 */
3170 }
3171
3172
3173
3174.SH IV. Writing
3175
3176Much of this is very similar to reading. However, everything of
3177importance is repeated here, so you won't have to constantly look
3178back up in the reading section to understand writing.
3179
3180.SS Setup
3181
3182You will want to do the I/O initialization before you get into libpng,
3183so if it doesn't work, you don't have anything to undo. If you are not
3184using the standard I/O functions, you will need to replace them with
3185custom writing functions. See the discussion under Customizing libpng.
3186
3187 FILE *fp = fopen(file_name, "wb");
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3188
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3189 if (!fp)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3190 return (ERROR);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3191
3192Next, png_struct and png_info need to be allocated and initialized.
3193As these can be both relatively large, you may not want to store these
3194on the stack, unless you have stack space to spare. Of course, you
3195will want to check if they return NULL. If you are also reading,
3196you won't want to name your read structure and your write structure
3197both "png_ptr"; you can call them anything you like, such as
3198"read_ptr" and "write_ptr". Look at pngtest.c, for example.
3199
3200 png_structp png_ptr = png_create_write_struct
3201 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3202 user_error_fn, user_warning_fn);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3203
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3204 if (!png_ptr)
3205 return (ERROR);
3206
3207 png_infop info_ptr = png_create_info_struct(png_ptr);
3208 if (!info_ptr)
3209 {
3210 png_destroy_write_struct(&png_ptr,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3211 (png_infopp)NULL);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3212 return (ERROR);
3213 }
3214
3215If you want to use your own memory allocation routines,
3216define PNG_USER_MEM_SUPPORTED and use
3217png_create_write_struct_2() instead of png_create_write_struct():
3218
3219 png_structp png_ptr = png_create_write_struct_2
3220 (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
3221 user_error_fn, user_warning_fn, (png_voidp)
3222 user_mem_ptr, user_malloc_fn, user_free_fn);
3223
3224After you have these structures, you will need to set up the
3225error handling. When libpng encounters an error, it expects to
3226longjmp() back to your routine. Therefore, you will need to call
3227setjmp() and pass the png_jmpbuf(png_ptr). If you
3228write the file from different routines, you will need to update
3229the png_jmpbuf(png_ptr) every time you enter a new routine that will
3230call a png_*() function. See your documentation of setjmp/longjmp
3231for your compiler for more information on setjmp/longjmp. See
3232the discussion on libpng error handling in the Customizing Libpng
3233section below for more information on the libpng error handling.
3234
3235 if (setjmp(png_jmpbuf(png_ptr)))
3236 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3237 png_destroy_write_struct(&png_ptr, &info_ptr);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3238 fclose(fp);
3239 return (ERROR);
3240 }
3241 ...
3242 return;
3243
3244If you would rather avoid the complexity of setjmp/longjmp issues,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3245you can compile libpng with PNG_NO_SETJMP, in which case
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3246errors will result in a call to PNG_ABORT() which defaults to abort().
3247
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3248You can #define PNG_ABORT() to a function that does something
3249more useful than abort(), as long as your function does not
3250return.
3251
3252Checking for invalid palette index on write was added at libpng
32531.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
3254a benign error. This is enabled by default because this condition is an
3255error according to the PNG specification, Clause 11.3.2, but the error can
3256be ignored in each png_ptr with
3257
3258 png_set_check_for_invalid_index(png_ptr, 0);
3259
3260If the error is ignored, or if png_benign_error() treats it as a warning,
3261any invalid pixels are written as-is by the encoder, resulting in an
3262invalid PNG datastream as output. In this case the application is
3263responsible for ensuring that the pixel indexes are in range when it writes
3264a PLTE chunk with fewer entries than the bit depth would allow.
3265
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3266Now you need to set up the output code. The default for libpng is to
3267use the C function fwrite(). If you use this, you will need to pass a
3268valid FILE * in the function png_init_io(). Be sure that the file is
3269opened in binary mode. Again, if you wish to handle writing data in
3270another way, see the discussion on libpng I/O handling in the Customizing
3271Libpng section below.
3272
3273 png_init_io(png_ptr, fp);
3274
3275If you are embedding your PNG into a datastream such as MNG, and don't
3276want libpng to write the 8-byte signature, or if you have already
3277written the signature in your application, use
3278
3279 png_set_sig_bytes(png_ptr, 8);
3280
3281to inform libpng that it should not write a signature.
3282
3283.SS Write callbacks
3284
3285At this point, you can set up a callback function that will be
3286called after each row has been written, which you can use to control
3287a progress meter or the like. It's demonstrated in pngtest.c.
3288You must supply a function
3289
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3290 void write_row_callback(png_structp png_ptr, png_uint_32 row,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3291 int pass);
3292 {
3293 /* put your code here */
3294 }
3295
3296(You can give it another name that you like instead of "write_row_callback")
3297
3298To inform libpng about your function, use
3299
3300 png_set_write_status_fn(png_ptr, write_row_callback);
3301
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3302When this function is called the row has already been completely processed and
3303it has also been written out. The 'row' and 'pass' refer to the next row to be
3304handled. For the
3305non-interlaced case the row that was just handled is simply one less than the
3306passed in row number, and pass will always be 0. For the interlaced case the
3307same applies unless the row value is 0, in which case the row just handled was
3308the last one from one of the preceding passes. Because interlacing may skip a
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]3309pass you cannot be sure that the preceding pass is just 'pass\-1', if you really
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3310need to know what the last pass is record (row,pass) from the callback and use
3311the last recorded value each time.
3312
3313As with the user transform you can find the output row using the
3314PNG_ROW_FROM_PASS_ROW macro.
3315
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3316You now have the option of modifying how the compression library will
3317run. The following functions are mainly for testing, but may be useful
3318in some cases, like if you need to write PNG files extremely fast and
3319are willing to give up some compression, or if you want to get the
3320maximum possible compression at the expense of slower writing. If you
3321have no special needs in this area, let the library do what it wants by
3322not calling this function at all, as it has been tuned to deliver a good
3323speed/compression ratio. The second parameter to png_set_filter() is
3324the filter method, for which the only valid values are 0 (as of the
3325July 1999 PNG specification, version 1.2) or 64 (if you are writing
3326a PNG datastream that is to be embedded in a MNG datastream). The third
3327parameter is a flag that indicates which filter type(s) are to be tested
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]3328for each scanline. See the PNG specification for details on the specific
3329filter types.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3330
3331
3332 /* turn on or off filtering, and/or choose
3333 specific filters. You can use either a single
3334 PNG_FILTER_VALUE_NAME or the bitwise OR of one
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3335 or more PNG_FILTER_NAME masks.
3336 */
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3337 png_set_filter(png_ptr, 0,
3338 PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
3339 PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
3340 PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]3341 PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3342 PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
3343 PNG_ALL_FILTERS);
3344
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3345If an application wants to start and stop using particular filters during
3346compression, it should start out with all of the filters (to ensure that
3347the previous row of pixels will be stored in case it's needed later),
3348and then add and remove them after the start of compression.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3349
3350If you are writing a PNG datastream that is to be embedded in a MNG
3351datastream, the second parameter can be either 0 or 64.
3352
3353The png_set_compression_*() functions interface to the zlib compression
3354library, and should mostly be ignored unless you really know what you are
3355doing. The only generally useful call is png_set_compression_level()
3356which changes how much time zlib spends on trying to compress the image
3357data. See the Compression Library (zlib.h and algorithm.txt, distributed
3358with zlib) for details on the compression levels.
3359
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3360 #include zlib.h
3361
3362 /* Set the zlib compression level */
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3363 png_set_compression_level(png_ptr,
3364 Z_BEST_COMPRESSION);
3365
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3366 /* Set other zlib parameters for compressing IDAT */
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3367 png_set_compression_mem_level(png_ptr, 8);
3368 png_set_compression_strategy(png_ptr,
3369 Z_DEFAULT_STRATEGY);
3370 png_set_compression_window_bits(png_ptr, 15);
3371 png_set_compression_method(png_ptr, 8);
3372 png_set_compression_buffer_size(png_ptr, 8192)
3373
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3374 /* Set zlib parameters for text compression
3375 * If you don't call these, the parameters
3376 * fall back on those defined for IDAT chunks
3377 */
3378 png_set_text_compression_mem_level(png_ptr, 8);
3379 png_set_text_compression_strategy(png_ptr,
3380 Z_DEFAULT_STRATEGY);
3381 png_set_text_compression_window_bits(png_ptr, 15);
3382 png_set_text_compression_method(png_ptr, 8);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3383
3384.SS Setting the contents of info for output
3385
3386You now need to fill in the png_info structure with all the data you
3387wish to write before the actual image. Note that the only thing you
3388are allowed to write after the image is the text chunks and the time
3389chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
3390the latest PNG specification for more information on that. If you
3391wish to write them before the image, fill them in now, and flag that
3392data as being valid. If you want to wait until after the data, don't
3393fill them until png_write_end(). For all the fields in png_info and
3394their data types, see png.h. For explanations of what the fields
3395contain, see the PNG specification.
3396
3397Some of the more important parts of the png_info are:
3398
3399 png_set_IHDR(png_ptr, info_ptr, width, height,
3400 bit_depth, color_type, interlace_type,
3401 compression_type, filter_method)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3402
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3403 width - holds the width of the image
3404 in pixels (up to 2^31).
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3405
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3406 height - holds the height of the image
3407 in pixels (up to 2^31).
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3408
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3409 bit_depth - holds the bit depth of one of the
3410 image channels.
3411 (valid values are 1, 2, 4, 8, 16
3412 and depend also on the
3413 color_type. See also significant
3414 bits (sBIT) below).
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3415
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3416 color_type - describes which color/alpha
3417 channels are present.
3418 PNG_COLOR_TYPE_GRAY
3419 (bit depths 1, 2, 4, 8, 16)
3420 PNG_COLOR_TYPE_GRAY_ALPHA
3421 (bit depths 8, 16)
3422 PNG_COLOR_TYPE_PALETTE
3423 (bit depths 1, 2, 4, 8)
3424 PNG_COLOR_TYPE_RGB
3425 (bit_depths 8, 16)
3426 PNG_COLOR_TYPE_RGB_ALPHA
3427 (bit_depths 8, 16)
3428
3429 PNG_COLOR_MASK_PALETTE
3430 PNG_COLOR_MASK_COLOR
3431 PNG_COLOR_MASK_ALPHA
3432
3433 interlace_type - PNG_INTERLACE_NONE or
3434 PNG_INTERLACE_ADAM7
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3435
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3436 compression_type - (must be
3437 PNG_COMPRESSION_TYPE_DEFAULT)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3438
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3439 filter_method - (must be PNG_FILTER_TYPE_DEFAULT
3440 or, if you are writing a PNG to
3441 be embedded in a MNG datastream,
3442 can also be
3443 PNG_INTRAPIXEL_DIFFERENCING)
3444
3445If you call png_set_IHDR(), the call must appear before any of the
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]3446other png_set_*() functions, because they might require access to some of
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3447the IHDR settings. The remaining png_set_*() functions can be called
3448in any order.
3449
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]3450If you wish, you can reset the compression_type, interlace_type, or
3451filter_method later by calling png_set_IHDR() again; if you do this, the
3452width, height, bit_depth, and color_type must be the same in each call.
3453
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3454 png_set_PLTE(png_ptr, info_ptr, palette,
3455 num_palette);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3456
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3457 palette - the palette for the file
3458 (array of png_color)
3459 num_palette - number of entries in the palette
3460
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3461 png_set_gAMA(png_ptr, info_ptr, file_gamma);
3462 png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
3463
3464 file_gamma - the gamma at which the image was
3465 created (PNG_INFO_gAMA)
3466
3467 int_file_gamma - 100,000 times the gamma at which
3468 the image was created
3469
3470 png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
3471 green_x, green_y, blue_x, blue_y)
3472 png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
3473 green_Y, green_Z, blue_X, blue_Y, blue_Z)
3474 png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
3475 int_red_x, int_red_y, int_green_x, int_green_y,
3476 int_blue_x, int_blue_y)
3477 png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
3478 int_red_Z, int_green_X, int_green_Y, int_green_Z,
3479 int_blue_X, int_blue_Y, int_blue_Z)
3480
3481 {white,red,green,blue}_{x,y}
3482 A color space encoding specified using the chromaticities
3483 of the end points and the white point.
3484
3485 {red,green,blue}_{X,Y,Z}
3486 A color space encoding specified using the encoding end
3487 points - the CIE tristimulus specification of the intended
3488 color of the red, green and blue channels in the PNG RGB
3489 data. The white point is simply the sum of the three end
3490 points.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3491
3492 png_set_sRGB(png_ptr, info_ptr, srgb_intent);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3493
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3494 srgb_intent - the rendering intent
3495 (PNG_INFO_sRGB) The presence of
3496 the sRGB chunk means that the pixel
3497 data is in the sRGB color space.
3498 This chunk also implies specific
3499 values of gAMA and cHRM. Rendering
3500 intent is the CSS-1 property that
3501 has been defined by the International
3502 Color Consortium
3503 (http://www.color.org).
3504 It can be one of
3505 PNG_sRGB_INTENT_SATURATION,
3506 PNG_sRGB_INTENT_PERCEPTUAL,
3507 PNG_sRGB_INTENT_ABSOLUTE, or
3508 PNG_sRGB_INTENT_RELATIVE.
3509
3510
3511 png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
3512 srgb_intent);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3513
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3514 srgb_intent - the rendering intent
3515 (PNG_INFO_sRGB) The presence of the
3516 sRGB chunk means that the pixel
3517 data is in the sRGB color space.
3518 This function also causes gAMA and
3519 cHRM chunks with the specific values
3520 that are consistent with sRGB to be
3521 written.
3522
3523 png_set_iCCP(png_ptr, info_ptr, name, compression_type,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3524 profile, proflen);
3525
3526 name - The profile name.
3527
3528 compression_type - The compression type; always
3529 PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
3530 You may give NULL to this argument to
3531 ignore it.
3532
3533 profile - International Color Consortium color
3534 profile data. May contain NULs.
3535
3536 proflen - length of profile data in bytes.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3537
3538 png_set_sBIT(png_ptr, info_ptr, sig_bit);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3539
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3540 sig_bit - the number of significant bits for
3541 (PNG_INFO_sBIT) each of the gray, red,
3542 green, and blue channels, whichever are
3543 appropriate for the given color type
3544 (png_color_16)
3545
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3546 png_set_tRNS(png_ptr, info_ptr, trans_alpha,
3547 num_trans, trans_color);
3548
3549 trans_alpha - array of alpha (transparency)
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]3550 entries for palette (PNG_INFO_tRNS)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3551
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3552 num_trans - number of transparent entries
3553 (PNG_INFO_tRNS)
3554
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3555 trans_color - graylevel or color sample values
3556 (in order red, green, blue) of the
3557 single transparent color for
3558 non-paletted images (PNG_INFO_tRNS)
3559
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3560 png_set_hIST(png_ptr, info_ptr, hist);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3561
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3562 hist - histogram of palette (array of
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3563 png_uint_16) (PNG_INFO_hIST)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3564
3565 png_set_tIME(png_ptr, info_ptr, mod_time);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3566
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3567 mod_time - time image was last modified
3568 (PNG_VALID_tIME)
3569
3570 png_set_bKGD(png_ptr, info_ptr, background);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3571
3572 background - background color (of type
3573 png_color_16p) (PNG_VALID_bKGD)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3574
3575 png_set_text(png_ptr, info_ptr, text_ptr, num_text);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3576
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3577 text_ptr - array of png_text holding image
3578 comments
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3579
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3580 text_ptr[i].compression - type of compression used
3581 on "text" PNG_TEXT_COMPRESSION_NONE
3582 PNG_TEXT_COMPRESSION_zTXt
3583 PNG_ITXT_COMPRESSION_NONE
3584 PNG_ITXT_COMPRESSION_zTXt
3585 text_ptr[i].key - keyword for comment. Must contain
3586 1-79 characters.
3587 text_ptr[i].text - text comments for current
3588 keyword. Can be NULL or empty.
3589 text_ptr[i].text_length - length of text string,
3590 after decompression, 0 for iTXt
3591 text_ptr[i].itxt_length - length of itxt string,
3592 after decompression, 0 for tEXt/zTXt
3593 text_ptr[i].lang - language of comment (NULL or
3594 empty for unknown).
3595 text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
3596 or empty for unknown).
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3597
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]3598 Note that the itxt_length, lang, and lang_key
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3599 members of the text_ptr structure only exist when the
3600 library is built with iTXt chunk support. Prior to
3601 libpng-1.4.0 the library was built by default without
3602 iTXt support. Also note that when iTXt is supported,
3603 they contain NULL pointers when the "compression"
3604 field contains PNG_TEXT_COMPRESSION_NONE or
3605 PNG_TEXT_COMPRESSION_zTXt.
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]3606
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3607 num_text - number of comments
3608
3609 png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
3610 num_spalettes);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3611
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3612 palette_ptr - array of png_sPLT_struct structures
3613 to be added to the list of palettes
3614 in the info structure.
3615 num_spalettes - number of palette structures to be
3616 added.
3617
3618 png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
3619 unit_type);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3620
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3621 offset_x - positive offset from the left
3622 edge of the screen
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3623
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3624 offset_y - positive offset from the top
3625 edge of the screen
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3626
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3627 unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
3628
3629 png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
3630 unit_type);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3631
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3632 res_x - pixels/unit physical resolution
3633 in x direction
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3634
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3635 res_y - pixels/unit physical resolution
3636 in y direction
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3637
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3638 unit_type - PNG_RESOLUTION_UNKNOWN,
3639 PNG_RESOLUTION_METER
3640
3641 png_set_sCAL(png_ptr, info_ptr, unit, width, height)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3642
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3643 unit - physical scale units (an integer)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3644
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3645 width - width of a pixel in physical scale units
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3646
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3647 height - height of a pixel in physical scale units
3648 (width and height are doubles)
3649
3650 png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3651
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3652 unit - physical scale units (an integer)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3653
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3654 width - width of a pixel in physical scale units
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3655 expressed as a string
3656
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3657 height - height of a pixel in physical scale units
3658 (width and height are strings like "2.54")
3659
3660 png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
3661 num_unknowns)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3662
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3663 unknowns - array of png_unknown_chunk
3664 structures holding unknown chunks
3665 unknowns[i].name - name of unknown chunk
3666 unknowns[i].data - data of unknown chunk
3667 unknowns[i].size - size of unknown chunk's data
3668 unknowns[i].location - position to write chunk in file
3669 0: do not write chunk
3670 PNG_HAVE_IHDR: before PLTE
3671 PNG_HAVE_PLTE: before IDAT
3672 PNG_AFTER_IDAT: after IDAT
3673
3674The "location" member is set automatically according to
3675what part of the output file has already been written.
3676You can change its value after calling png_set_unknown_chunks()
3677as demonstrated in pngtest.c. Within each of the "locations",
3678the chunks are sequenced according to their position in the
3679structure (that is, the value of "i", which is the order in which
3680the chunk was either read from the input file or defined with
3681png_set_unknown_chunks).
3682
3683A quick word about text and num_text. text is an array of png_text
3684structures. num_text is the number of valid structures in the array.
3685Each png_text structure holds a language code, a keyword, a text value,
3686and a compression type.
3687
3688The compression types have the same valid numbers as the compression
3689types of the image data. Currently, the only valid number is zero.
3690However, you can store text either compressed or uncompressed, unlike
3691images, which always have to be compressed. So if you don't want the
3692text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
3693Because tEXt and zTXt chunks don't have a language field, if you
3694specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
3695any language code or translated keyword will not be written out.
3696
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3697Until text gets around a few hundred bytes, it is not worth compressing it.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3698After the text has been written out to the file, the compression type
3699is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
3700so that it isn't written out again at the end (in case you are calling
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3701png_write_end() with the same struct).
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3702
3703The keywords that are given in the PNG Specification are:
3704
3705 Title Short (one line) title or
3706 caption for image
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3707
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3708 Author Name of image's creator
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3709
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3710 Description Description of image (possibly long)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3711
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3712 Copyright Copyright notice
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3713
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3714 Creation Time Time of original image creation
3715 (usually RFC 1123 format, see below)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3716
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3717 Software Software used to create the image
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3718
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3719 Disclaimer Legal disclaimer
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3720
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3721 Warning Warning of nature of content
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3722
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3723 Source Device used to create the image
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3724
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3725 Comment Miscellaneous comment; conversion
3726 from other image format
3727
3728The keyword-text pairs work like this. Keywords should be short
3729simple descriptions of what the comment is about. Some typical
3730keywords are found in the PNG specification, as is some recommendations
3731on keywords. You can repeat keywords in a file. You can even write
3732some text before the image and some after. For example, you may want
3733to put a description of the image before the image, but leave the
3734disclaimer until after, so viewers working over modem connections
3735don't have to wait for the disclaimer to go over the modem before
3736they start seeing the image. Finally, keywords should be full
3737words, not abbreviations. Keywords and text are in the ISO 8859-1
3738(Latin-1) character set (a superset of regular ASCII) and can not
3739contain NUL characters, and should not contain control or other
3740unprintable characters. To make the comments widely readable, stick
3741with basic ASCII, and avoid machine specific character set extensions
3742like the IBM-PC character set. The keyword must be present, but
3743you can leave off the text string on non-compressed pairs.
3744Compressed pairs must have a text string, as only the text string
3745is compressed anyway, so the compression would be meaningless.
3746
3747PNG supports modification time via the png_time structure. Two
3748conversion routines are provided, png_convert_from_time_t() for
3749time_t and png_convert_from_struct_tm() for struct tm. The
3750time_t routine uses gmtime(). You don't have to use either of
3751these, but if you wish to fill in the png_time structure directly,
3752you should provide the time in universal time (GMT) if possible
3753instead of your local time. Note that the year number is the full
3754year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
3755that months start with 1.
3756
3757If you want to store the time of the original image creation, you should
3758use a plain tEXt chunk with the "Creation Time" keyword. This is
3759necessary because the "creation time" of a PNG image is somewhat vague,
3760depending on whether you mean the PNG file, the time the image was
3761created in a non-PNG format, a still photo from which the image was
3762scanned, or possibly the subject matter itself. In order to facilitate
3763machine-readable dates, it is recommended that the "Creation Time"
3764tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
3765although this isn't a requirement. Unlike the tIME chunk, the
3766"Creation Time" tEXt chunk is not expected to be automatically changed
3767by the software. To facilitate the use of RFC 1123 dates, a function
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3768png_convert_to_rfc1123_buffer(png_ptr, buffer, png_timep) is provided to
3769convert from PNG time to an RFC 1123 format string. The caller must provide
3770a writeable buffer of at least 29 bytes.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3771
3772.SS Writing unknown chunks
3773
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3774You can use the png_set_unknown_chunks function to queue up private chunks
3775for writing. You give it a chunk name, location, raw data, and a size. You
3776also must use png_set_keep_unknown_chunks() to ensure that libpng will
3777handle them. That's all there is to it. The chunks will be written by the
3778next following png_write_info_before_PLTE, png_write_info, or png_write_end
3779function, depending upon the specified location. Any chunks previously
3780read into the info structure's unknown-chunk list will also be written out
3781in a sequence that satisfies the PNG specification's ordering rules.
3782
3783Here is an example of writing two private chunks, prVt and miNE:
3784
3785 #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
3786 /* Set unknown chunk data */
3787 png_unknown_chunk unk_chunk[2];
3788 strcpy((char *) unk_chunk[0].name, "prVt";
3789 unk_chunk[0].data = (unsigned char *) "PRIVATE DATA";
3790 unk_chunk[0].size = strlen(unk_chunk[0].data)+1;
3791 unk_chunk[0].location = PNG_HAVE_IHDR;
3792 strcpy((char *) unk_chunk[1].name, "miNE";
3793 unk_chunk[1].data = (unsigned char *) "MY CHUNK DATA";
3794 unk_chunk[1].size = strlen(unk_chunk[0].data)+1;
3795 unk_chunk[1].location = PNG_AFTER_IDAT;
3796 png_set_unknown_chunks(write_ptr, write_info_ptr,
3797 unk_chunk, 2);
3798 /* Needed because miNE is not safe-to-copy */
3799 png_set_keep_unknown_chunks(png, PNG_HANDLE_CHUNK_ALWAYS,
3800 (png_bytep) "miNE", 1);
3801 # if PNG_LIBPNG_VER < 10600
3802 /* Deal with unknown chunk location bug in 1.5.x and earlier */
3803 png_set_unknown_chunk_location(png, info, 0, PNG_HAVE_IHDR);
3804 png_set_unknown_chunk_location(png, info, 1, PNG_AFTER_IDAT);
3805 # endif
3806 # if PNG_LIBPNG_VER < 10500
3807 /* PNG_AFTER_IDAT writes two copies of the chunk prior to libpng-1.5.0,
3808 * one before IDAT and another after IDAT, so don't use it; only use
3809 * PNG_HAVE_IHDR location. This call resets the location previously
3810 * set by assignment and png_set_unknown_chunk_location() for chunk 1.
3811 */
3812 png_set_unknown_chunk_location(png, info, 1, PNG_HAVE_IHDR);
3813 # endif
3814 #endif
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3815
3816.SS The high-level write interface
3817
3818At this point there are two ways to proceed; through the high-level
3819write interface, or through a sequence of low-level write operations.
3820You can use the high-level interface if your image data is present
3821in the info structure. All defined output
3822transformations are permitted, enabled by the following masks.
3823
3824 PNG_TRANSFORM_IDENTITY No transformation
3825 PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
3826 PNG_TRANSFORM_PACKSWAP Change order of packed
3827 pixels to LSB first
3828 PNG_TRANSFORM_INVERT_MONO Invert monochrome images
3829 PNG_TRANSFORM_SHIFT Normalize pixels to the
3830 sBIT depth
3831 PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
3832 to BGRA
3833 PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
3834 to AG
3835 PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
3836 to transparency
3837 PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]3838 PNG_TRANSFORM_STRIP_FILLER Strip out filler
3839 bytes (deprecated).
3840 PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
3841 filler bytes
3842 PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
3843 filler bytes
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3844
3845If you have valid image data in the info structure (you can use
3846png_set_rows() to put image data in the info structure), simply do this:
3847
3848 png_write_png(png_ptr, info_ptr, png_transforms, NULL)
3849
3850where png_transforms is an integer containing the bitwise OR of some set of
3851transformation flags. This call is equivalent to png_write_info(),
3852followed the set of transformations indicated by the transform mask,
3853then png_write_image(), and finally png_write_end().
3854
3855(The final parameter of this call is not yet used. Someday it might point
3856to transformation parameters required by some future output transform.)
3857
3858You must use png_transforms and not call any png_set_transform() functions
3859when you use png_write_png().
3860
3861.SS The low-level write interface
3862
3863If you are going the low-level route instead, you are now ready to
3864write all the file information up to the actual image data. You do
3865this with a call to png_write_info().
3866
3867 png_write_info(png_ptr, info_ptr);
3868
3869Note that there is one transformation you may need to do before
3870png_write_info(). In PNG files, the alpha channel in an image is the
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]3871level of opacity. If your data is supplied as a level of transparency,
3872you can invert the alpha channel before you write it, so that 0 is
3873fully transparent and 255 (in 8-bit or paletted images) or 65535
3874(in 16-bit images) is fully opaque, with
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3875
3876 png_set_invert_alpha(png_ptr);
3877
3878This must appear before png_write_info() instead of later with the
3879other transformations because in the case of paletted images the tRNS
3880chunk data has to be inverted before the tRNS chunk is written. If
3881your image is not a paletted image, the tRNS data (which in such cases
3882represents a single color to be rendered as transparent) won't need to
3883be changed, and you can safely do this transformation after your
3884png_write_info() call.
3885
3886If you need to write a private chunk that you want to appear before
3887the PLTE chunk when PLTE is present, you can write the PNG info in
3888two steps, and insert code to write your own chunk between them:
3889
3890 png_write_info_before_PLTE(png_ptr, info_ptr);
3891 png_set_unknown_chunks(png_ptr, info_ptr, ...);
3892 png_write_info(png_ptr, info_ptr);
3893
3894After you've written the file information, you can set up the library
3895to handle any special transformations of the image data. The various
3896ways to transform the data will be described in the order that they
3897should occur. This is important, as some of these change the color
3898type and/or bit depth of the data, and some others only work on
3899certain color types and bit depths. Even though each transformation
3900checks to see if it has data that it can do something with, you should
3901make sure to only enable a transformation if it will be valid for the
3902data. For example, don't swap red and blue on grayscale data.
3903
3904PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
3905the library to strip input data that has 4 or 8 bytes per pixel down
3906to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
3907bytes per pixel).
3908
3909 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
3910
3911where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
3912PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
3913is stored XRGB or RGBX.
3914
3915PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
3916they can, resulting in, for example, 8 pixels per byte for 1 bit files.
3917If the data is supplied at 1 pixel per byte, use this code, which will
3918correctly pack the pixels into a single byte:
3919
3920 png_set_packing(png_ptr);
3921
3922PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
3923data is of another bit depth, you can write an sBIT chunk into the
3924file so that decoders can recover the original data if desired.
3925
3926 /* Set the true bit depth of the image data */
3927 if (color_type & PNG_COLOR_MASK_COLOR)
3928 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3929 sig_bit.red = true_bit_depth;
3930 sig_bit.green = true_bit_depth;
3931 sig_bit.blue = true_bit_depth;
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3932 }
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3933
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3934 else
3935 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3936 sig_bit.gray = true_bit_depth;
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3937 }
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3938
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3939 if (color_type & PNG_COLOR_MASK_ALPHA)
3940 {
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3941 sig_bit.alpha = true_bit_depth;
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3942 }
3943
3944 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
3945
3946If the data is stored in the row buffer in a bit depth other than
3947one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
3948this will scale the values to appear to be the correct bit depth as
3949is required by PNG.
3950
3951 png_set_shift(png_ptr, &sig_bit);
3952
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3953PNG files store 16-bit pixels in network byte order (big-endian,
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3954ie. most significant bits first). This code would be used if they are
3955supplied the other way (little-endian, i.e. least significant bits
3956first, the way PCs store them):
3957
3958 if (bit_depth > 8)
3959 png_set_swap(png_ptr);
3960
3961If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
3962need to change the order the pixels are packed into bytes, you can use:
3963
3964 if (bit_depth < 8)
3965 png_set_packswap(png_ptr);
3966
3967PNG files store 3 color pixels in red, green, blue order. This code
3968would be used if they are supplied as blue, green, red:
3969
3970 png_set_bgr(png_ptr);
3971
3972PNG files describe monochrome as black being zero and white being
3973one. This code would be used if the pixels are supplied with this reversed
3974(black being one and white being zero):
3975
3976 png_set_invert_mono(png_ptr);
3977
3978Finally, you can write your own transformation function if none of
3979the existing ones meets your needs. This is done by setting a callback
3980with
3981
3982 png_set_write_user_transform_fn(png_ptr,
3983 write_transform_fn);
3984
3985You must supply the function
3986
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3987 void write_transform_fn(png_structp png_ptr, png_row_infop
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]3988 row_info, png_bytep data)
3989
3990See pngtest.c for a working example. Your function will be called
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]3991before any of the other transformations are processed. If supported
3992libpng also supplies an information routine that may be called from
3993your callback:
3994
3995 png_get_current_row_number(png_ptr);
3996 png_get_current_pass_number(png_ptr);
3997
3998This returns the current row passed to the transform. With interlaced
3999images the value returned is the row in the input sub-image image. Use
4000PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
4001find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
4002
4003The discussion of interlace handling above contains more information on how to
4004use these values.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4005
4006You can also set up a pointer to a user structure for use by your
4007callback function.
4008
4009 png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
4010
4011The user_channels and user_depth parameters of this function are ignored
4012when writing; you can set them to zero as shown.
4013
4014You can retrieve the pointer via the function png_get_user_transform_ptr().
4015For example:
4016
4017 voidp write_user_transform_ptr =
4018 png_get_user_transform_ptr(png_ptr);
4019
4020It is possible to have libpng flush any pending output, either manually,
4021or automatically after a certain number of lines have been written. To
4022flush the output stream a single time call:
4023
4024 png_write_flush(png_ptr);
4025
4026and to have libpng flush the output stream periodically after a certain
4027number of scanlines have been written, call:
4028
4029 png_set_flush(png_ptr, nrows);
4030
4031Note that the distance between rows is from the last time png_write_flush()
4032was called, or the first row of the image if it has never been called.
4033So if you write 50 lines, and then png_set_flush 25, it will flush the
4034output on the next scanline, and every 25 lines thereafter, unless
4035png_write_flush() is called before 25 more lines have been written.
4036If nrows is too small (less than about 10 lines for a 640 pixel wide
4037RGB image) the image compression may decrease noticeably (although this
4038may be acceptable for real-time applications). Infrequent flushing will
4039only degrade the compression performance by a few percent over images
4040that do not use flushing.
4041
4042.SS Writing the image data
4043
4044That's it for the transformations. Now you can write the image data.
4045The simplest way to do this is in one function call. If you have the
4046whole image in memory, you can just call png_write_image() and libpng
4047will write the image. You will need to pass in an array of pointers to
4048each row. This function automatically handles interlacing, so you don't
4049need to call png_set_interlace_handling() or call this function multiple
4050times, or any of that other stuff necessary with png_write_rows().
4051
4052 png_write_image(png_ptr, row_pointers);
4053
4054where row_pointers is:
4055
4056 png_byte *row_pointers[height];
4057
4058You can point to void or char or whatever you use for pixels.
4059
4060If you don't want to write the whole image at once, you can
4061use png_write_rows() instead. If the file is not interlaced,
4062this is simple:
4063
4064 png_write_rows(png_ptr, row_pointers,
4065 number_of_rows);
4066
4067row_pointers is the same as in the png_write_image() call.
4068
4069If you are just writing one row at a time, you can do this with
4070a single row_pointer instead of an array of row_pointers:
4071
4072 png_bytep row_pointer = row;
4073
4074 png_write_row(png_ptr, row_pointer);
4075
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]4076When the file is interlaced, things can get a good deal more complicated.
4077The only currently (as of the PNG Specification version 1.2, dated July
40781999) defined interlacing scheme for PNG files is the "Adam7" interlace
4079scheme, that breaks down an image into seven smaller images of varying
4080size. libpng will build these images for you, or you can do them
4081yourself. If you want to build them yourself, see the PNG specification
4082for details of which pixels to write when.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4083
4084If you don't want libpng to handle the interlacing details, just
4085use png_set_interlace_handling() and call png_write_rows() the
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4086correct number of times to write all the sub-images
4087(png_set_interlace_handling() returns the number of sub-images.)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4088
4089If you want libpng to build the sub-images, call this before you start
4090writing any rows:
4091
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4092 number_of_passes = png_set_interlace_handling(png_ptr);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4093
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]4094This will return the number of passes needed. Currently, this is seven,
4095but may change if another interlace type is added.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4096
4097Then write the complete image number_of_passes times.
4098
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4099 png_write_rows(png_ptr, row_pointers, number_of_rows);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4100
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4101Think carefully before you write an interlaced image. Typically code that
4102reads such images reads all the image data into memory, uncompressed, before
4103doing any processing. Only code that can display an image on the fly can
4104take advantage of the interlacing and even then the image has to be exactly
4105the correct size for the output device, because scaling an image requires
4106adjacent pixels and these are not available until all the passes have been
4107read.
4108
4109If you do write an interlaced image you will hardly ever need to handle
4110the interlacing yourself. Call png_set_interlace_handling() and use the
4111approach described above.
4112
4113The only time it is conceivable that you will really need to write an
4114interlaced image pass-by-pass is when you have read one pass by pass and
4115made some pixel-by-pixel transformation to it, as described in the read
4116code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
4117to determine the size of each sub-image in turn and simply write the rows
4118you obtained from the read code.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4119
4120.SS Finishing a sequential write
4121
4122After you are finished writing the image, you should finish writing
4123the file. If you are interested in writing comments or time, you should
4124pass an appropriately filled png_info pointer. If you are not interested,
4125you can pass NULL.
4126
4127 png_write_end(png_ptr, info_ptr);
4128
4129When you are done, you can free all memory used by libpng like this:
4130
4131 png_destroy_write_struct(&png_ptr, &info_ptr);
4132
4133It is also possible to individually free the info_ptr members that
4134point to libpng-allocated storage with the following function:
4135
4136 png_free_data(png_ptr, info_ptr, mask, seq)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4137
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4138 mask - identifies data to be freed, a mask
4139 containing the bitwise OR of one or
4140 more of
4141 PNG_FREE_PLTE, PNG_FREE_TRNS,
4142 PNG_FREE_HIST, PNG_FREE_ICCP,
4143 PNG_FREE_PCAL, PNG_FREE_ROWS,
4144 PNG_FREE_SCAL, PNG_FREE_SPLT,
4145 PNG_FREE_TEXT, PNG_FREE_UNKN,
4146 or simply PNG_FREE_ALL
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4147
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4148 seq - sequence number of item to be freed
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]4149 (\-1 for all items)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4150
4151This function may be safely called when the relevant storage has
4152already been freed, or has not yet been allocated, or was allocated
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]4153by the user and not by libpng, and will in those cases do nothing.
4154The "seq" parameter is ignored if only one item of the selected data
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]4155type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]4156are allowed for the data type identified in the mask, such as text or
4157sPLT, only the n'th item in the structure is freed, where n is "seq".
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4158
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]4159If you allocated data such as a palette that you passed in to libpng
4160with png_set_*, you must not free it until just before the call to
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4161png_destroy_write_struct().
4162
4163The default behavior is only to free data that was allocated internally
4164by libpng. This can be changed, so that libpng will not free the data,
4165or so that it will free data that was allocated by the user with png_malloc()
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4166or png_calloc() and passed in via a png_set_*() function, with
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4167
4168 png_data_freer(png_ptr, info_ptr, freer, mask)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4169
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4170 freer - one of
4171 PNG_DESTROY_WILL_FREE_DATA
4172 PNG_SET_WILL_FREE_DATA
4173 PNG_USER_WILL_FREE_DATA
4174
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4175 mask - which data elements are affected
4176 same choices as in png_free_data()
4177
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4178For example, to transfer responsibility for some data from a read structure
4179to a write structure, you could use
4180
4181 png_data_freer(read_ptr, read_info_ptr,
4182 PNG_USER_WILL_FREE_DATA,
4183 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4184
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4185 png_data_freer(write_ptr, write_info_ptr,
4186 PNG_DESTROY_WILL_FREE_DATA,
4187 PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
4188
4189thereby briefly reassigning responsibility for freeing to the user but
4190immediately afterwards reassigning it once more to the write_destroy
4191function. Having done this, it would then be safe to destroy the read
4192structure and continue to use the PLTE, tRNS, and hIST data in the write
4193structure.
4194
4195This function only affects data that has already been allocated.
4196You can call this function before calling after the png_set_*() functions
4197to control whether the user or png_destroy_*() is supposed to free the data.
4198When the user assumes responsibility for libpng-allocated data, the
4199application must use
4200png_free() to free it, and when the user transfers responsibility to libpng
4201for data that the user has allocated, the user must have used png_malloc()
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4202or png_calloc() to allocate it.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4203
4204If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
4205separately, do not transfer responsibility for freeing text_ptr to libpng,
4206because when libpng fills a png_text structure it combines these members with
4207the key member, and png_free_data() will free only text_ptr.key. Similarly,
4208if you transfer responsibility for free'ing text_ptr from libpng to your
4209application, your application must not separately free those members.
4210For a more compact example of writing a PNG image, see the file example.c.
4211
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4212.SH V. Simplified API
4213
4214The simplified API, which became available in libpng-1.6.0, hides the details
4215of both libpng and the PNG file format itself.
4216It allows PNG files to be read into a very limited number of
4217in-memory bitmap formats or to be written from the same formats. If these
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]4218formats do not accommodate your needs then you can, and should, use the more
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4219sophisticated APIs above - these support a wide variety of in-memory formats
4220and a wide variety of sophisticated transformations to those formats as well
4221as a wide variety of APIs to manipulate ancilliary information.
4222
4223To read a PNG file using the simplified API:
4224
4225 1) Declare a 'png_image' structure (see below) on the
4226 stack and memset() it to all zero.
4227
4228 2) Call the appropriate png_image_begin_read... function.
4229
4230 3) Set the png_image 'format' member to the required
4231 format and allocate a buffer for the image.
4232
4233 4) Call png_image_finish_read to read the image into
4234 your buffer.
4235
4236There are no restrictions on the format of the PNG input itself; all valid
4237color types, bit depths, and interlace methods are acceptable, and the
4238input image is transformed as necessary to the requested in-memory format
4239during the png_image_finish_read() step.
4240
4241To write a PNG file using the simplified API:
4242
4243 1) Declare a 'png_image' structure on the stack and memset()
4244 it to all zero.
4245
4246 2) Initialize the members of the structure that describe the
4247 image, setting the 'format' member to the format of the
4248 image in memory.
4249
4250 3) Call the appropriate png_image_write... function with a
4251 pointer to the image to write the PNG data.
4252
4253png_image is a structure that describes the in-memory format of an image
4254when it is being read or define the in-memory format of an image that you
4255need to write. The "png_image" structure contains the following members:
4256
4257 png_uint_32 version Set to PNG_IMAGE_VERSION
4258 png_uint_32 width Image width in pixels (columns)
4259 png_uint_32 height Image height in pixels (rows)
4260 png_uint_32 format Image format as defined below
4261 png_uint_32 flags A bit mask containing informational flags
4262 png_controlp opaque Initialize to NULL, free with png_image_free
4263 png_uint_32 colormap_entries; Number of entries in the color-map
4264 png_uint_32 warning_or_error;
4265 char message[64];
4266
4267In the event of an error or warning the following field warning_or_error
4268field will be set to a non-zero value and the 'message' field will contain
4269a '\0' terminated string with the libpng error or warning message. If both
4270warnings and an error were encountered, only the error is recorded. If there
4271are multiple warnings, only the first one is recorded.
4272
4273The upper 30 bits of this value are reserved; the low two bits contain
4274a two bit code such that a value more than 1 indicates a failure in the API
4275just called:
4276
4277 0 - no warning or error
4278 1 - warning
4279 2 - error
4280 3 - error preceded by warning
4281
4282The pixels (samples) of the image have one to four channels whose components
4283have original values in the range 0 to 1.0:
4284
4285 1: A single gray or luminance channel (G).
4286 2: A gray/luminance channel and an alpha channel (GA).
4287 3: Three red, green, blue color channels (RGB).
4288 4: Three color channels and an alpha channel (RGBA).
4289
4290The channels are encoded in one of two ways:
4291
4292 a) As a small integer, value 0..255, contained in a single byte. For the
4293alpha channel the original value is simply value/255. For the color or
4294luminance channels the value is encoded according to the sRGB specification
4295and matches the 8-bit format expected by typical display devices.
4296
4297The color/gray channels are not scaled (pre-multiplied) by the alpha
4298channel and are suitable for passing to color management software.
4299
4300 b) As a value in the range 0..65535, contained in a 2-byte integer. All
4301channels can be converted to the original value by dividing by 65535; all
4302channels are linear. Color channels use the RGB encoding (RGB end-points) of
4303the sRGB specification. This encoding is identified by the
4304PNG_FORMAT_FLAG_LINEAR flag below.
4305
4306When an alpha channel is present it is expected to denote pixel coverage
4307of the color or luminance channels and is returned as an associated alpha
4308channel: the color/gray channels are scaled (pre-multiplied) by the alpha
4309value.
4310
4311When a color-mapped image is used as a result of calling
4312png_image_read_colormap or png_image_write_colormap the channels are encoded
4313in the color-map and the descriptions above apply to the color-map entries.
4314The image data is encoded as small integers, value 0..255, that index the
4315entries in the color-map. One integer (one byte) is stored for each pixel.
4316
4317PNG_FORMAT_*
4318
4319The #defines to be used in png_image::format. Each #define identifies a
4320particular layout of channel data and, if present, alpha values. There are
4321separate defines for each of the two channel encodings.
4322
4323A format is built up using single bit flag values. Not all combinations are
4324valid: use the bit flag values below for testing a format returned by the
4325read APIs, but set formats from the derived values.
4326
4327When reading or writing color-mapped images the format should be set to the
4328format of the entries in the color-map then png_image_{read,write}_colormap
4329called to read or write the color-map and set the format correctly for the
4330image data. Do not set the PNG_FORMAT_FLAG_COLORMAP bit directly!
4331
4332NOTE: libpng can be built with particular features disabled, if you see
4333compiler errors because the definition of one of the following flags has been
4334compiled out it is because libpng does not have the required support. It is
4335possible, however, for the libpng configuration to enable the format on just
4336read or just write; in that case you may see an error at run time. You can
4337guard against this by checking for the definition of:
4338
4339 PNG_SIMPLIFIED_{READ,WRITE}_{BGR,AFIRST}_SUPPORTED
4340
4341 PNG_FORMAT_FLAG_ALPHA 0x01 format with an alpha channel
4342 PNG_FORMAT_FLAG_COLOR 0x02 color format: otherwise grayscale
4343 PNG_FORMAT_FLAG_LINEAR 0x04 png_uint_16 channels else png_byte
4344 PNG_FORMAT_FLAG_COLORMAP 0x08 libpng use only
4345 PNG_FORMAT_FLAG_BGR 0x10 BGR colors, else order is RGB
4346 PNG_FORMAT_FLAG_AFIRST 0x20 alpha channel comes first
4347
4348Supported formats are as follows. Future versions of libpng may support more
4349formats; for compatibility with older versions simply check if the format
4350macro is defined using #ifdef. These defines describe the in-memory layout
4351of the components of the pixels of the image.
4352
4353First the single byte formats:
4354
4355 PNG_FORMAT_GRAY 0
4356 PNG_FORMAT_GA PNG_FORMAT_FLAG_ALPHA
4357 PNG_FORMAT_AG (PNG_FORMAT_GA|PNG_FORMAT_FLAG_AFIRST)
4358 PNG_FORMAT_RGB PNG_FORMAT_FLAG_COLOR
4359 PNG_FORMAT_BGR (PNG_FORMAT_FLAG_COLOR|PNG_FORMAT_FLAG_BGR)
4360 PNG_FORMAT_RGBA (PNG_FORMAT_RGB|PNG_FORMAT_FLAG_ALPHA)
4361 PNG_FORMAT_ARGB (PNG_FORMAT_RGBA|PNG_FORMAT_FLAG_AFIRST)
4362 PNG_FORMAT_BGRA (PNG_FORMAT_BGR|PNG_FORMAT_FLAG_ALPHA)
4363 PNG_FORMAT_ABGR (PNG_FORMAT_BGRA|PNG_FORMAT_FLAG_AFIRST)
4364
4365Then the linear 2-byte formats. When naming these "Y" is used to
4366indicate a luminance (gray) channel. The component order within the pixel
4367is always the same - there is no provision for swapping the order of the
4368components in the linear format.
4369
4370 PNG_FORMAT_LINEAR_Y PNG_FORMAT_FLAG_LINEAR
4371 PNG_FORMAT_LINEAR_Y_ALPHA
4372 (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_ALPHA)
4373 PNG_FORMAT_LINEAR_RGB
4374 (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_COLOR)
4375 PNG_FORMAT_LINEAR_RGB_ALPHA
4376 (PNG_FORMAT_FLAG_LINEAR|PNG_FORMAT_FLAG_COLOR|
4377 PNG_FORMAT_FLAG_ALPHA)
4378
4379Color-mapped formats are obtained by calling png_image_{read,write}_colormap,
4380as appropriate after setting png_image::format to the format of the color-map
4381to be read or written. Applications may check the value of
4382PNG_FORMAT_FLAG_COLORMAP to see if they have called the colormap API. The
4383format of the color-map may be extracted using the following macro.
4384
4385 PNG_FORMAT_OF_COLORMAP(fmt) ((fmt) & ~PNG_FORMAT_FLAG_COLORMAP)
4386
4387PNG_IMAGE macros
4388
4389These are convenience macros to derive information from a png_image
4390structure. The PNG_IMAGE_SAMPLE_ macros return values appropriate to the
4391actual image sample values - either the entries in the color-map or the
4392pixels in the image. The PNG_IMAGE_PIXEL_ macros return corresponding values
4393for the pixels and will always return 1 after a call to
4394png_image_{read,write}_colormap. The remaining macros return information
4395about the rows in the image and the complete image.
4396
4397NOTE: All the macros that take a png_image::format parameter are compile time
4398constants if the format parameter is, itself, a constant. Therefore these
4399macros can be used in array declarations and case labels where required.
4400Similarly the macros are also pre-processor constants (sizeof is not used) so
4401they can be used in #if tests.
4402
4403First the information about the samples.
4404
4405 PNG_IMAGE_SAMPLE_CHANNELS(fmt)
4406 Returns the total number of channels in a given format: 1..4
4407
4408 PNG_IMAGE_SAMPLE_COMPONENT_SIZE(fmt)
4409 Returns the size in bytes of a single component of a pixel or color-map
4410 entry (as appropriate) in the image.
4411
4412 PNG_IMAGE_SAMPLE_SIZE(fmt)
4413 This is the size of the sample data for one sample. If the image is
4414 color-mapped it is the size of one color-map entry (and image pixels are
4415 one byte in size), otherwise it is the size of one image pixel.
4416
4417 PNG_IMAGE_COLORMAP_SIZE(fmt)
4418 The size of the color-map required by the format; this is the size of the
4419 color-map buffer passed to the png_image_{read,write}_colormap APIs, it is
4420 a fixed number determined by the format so can easily be allocated on the
4421 stack if necessary.
4422
4423#define PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(fmt)\
4424 (PNG_IMAGE_SAMPLE_CHANNELS(fmt) * 256)
4425 /* The maximum size of the color-map required by the format expressed in a
4426 * count of components. This can be used to compile-time allocate a
4427 * color-map:
4428 *
4429 * png_uint_16 colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(linear_fmt)];
4430 *
4431 * png_byte colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(sRGB_fmt)];
4432 *
4433 * Alternatively use the PNG_IMAGE_COLORMAP_SIZE macro below to use the
4434 * information from one of the png_image_begin_read_ APIs and dynamically
4435 * allocate the required memory.
4436 */
4437
4438
4439Corresponding information about the pixels
4440
4441 PNG_IMAGE_PIXEL_(test,fmt)
4442
4443 PNG_IMAGE_PIXEL_CHANNELS(fmt)
4444 The number of separate channels (components) in a pixel; 1 for a
4445 color-mapped image.
4446
4447 PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)\
4448 The size, in bytes, of each component in a pixel; 1 for a color-mapped
4449 image.
4450
4451 PNG_IMAGE_PIXEL_SIZE(fmt)
4452 The size, in bytes, of a complete pixel; 1 for a color-mapped image.
4453
4454Information about the whole row, or whole image
4455
4456 PNG_IMAGE_ROW_STRIDE(image)
4457 Returns the total number of components in a single row of the image; this
4458 is the minimum 'row stride', the minimum count of components between each
4459 row. For a color-mapped image this is the minimum number of bytes in a
4460 row.
4461
4462 PNG_IMAGE_BUFFER_SIZE(image, row_stride)
4463 Returns the size, in bytes, of an image buffer given a png_image and a row
4464 stride - the number of components to leave space for in each row.
4465
4466 PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB == 0x01
4467 This indicates the the RGB values of the in-memory bitmap do not
4468 correspond to the red, green and blue end-points defined by sRGB.
4469
4470 PNG_IMAGE_FLAG_COLORMAP == 0x02
4471 The PNG is color-mapped. If this flag is set png_image_read_colormap
4472 can be used without further loss of image information. If it is not set
4473 png_image_read_colormap will cause significant loss if the image has any
4474
4475READ APIs
4476
4477 The png_image passed to the read APIs must have been initialized by setting
4478 the png_controlp field 'opaque' to NULL (or, better, memset the whole thing.)
4479
4480 int png_image_begin_read_from_file( png_imagep image,
4481 const char *file_name)
4482
4483 The named file is opened for read and the image header
4484 is filled in from the PNG header in the file.
4485
4486 int png_image_begin_read_from_stdio (png_imagep image,
4487 FILE* file)
4488
4489 The PNG header is read from the stdio FILE object.
4490
4491 int png_image_begin_read_from_memory(png_imagep image,
4492 png_const_voidp memory, png_size_t size)
4493
4494 The PNG header is read from the given memory buffer.
4495
4496 int png_image_finish_read(png_imagep image,
4497 png_colorp background, void *buffer,
4498 png_int_32 row_stride, void *colormap));
4499
4500 Finish reading the image into the supplied buffer and
4501 clean up the png_image structure.
4502
4503 row_stride is the step, in png_byte or png_uint_16 units
4504 as appropriate, between adjacent rows. A positive stride
4505 indicates that the top-most row is first in the buffer -
4506 the normal top-down arrangement. A negative stride
4507 indicates that the bottom-most row is first in the buffer.
4508
4509 background need only be supplied if an alpha channel must
4510 be removed from a png_byte format and the removal is to be
4511 done by compositing on a solid color; otherwise it may be
4512 NULL and any composition will be done directly onto the
4513 buffer. The value is an sRGB color to use for the
4514 background, for grayscale output the green channel is used.
4515
4516 For linear output removing the alpha channel is always done
4517 by compositing on black.
4518
4519 void png_image_free(png_imagep image)
4520
4521 Free any data allocated by libpng in image->opaque,
4522 setting the pointer to NULL. May be called at any time
4523 after the structure is initialized.
4524
4525When the simplified API needs to convert between sRGB and linear colorspaces,
4526the actual sRGB transfer curve defined in the sRGB specification (see the
4527article at http://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
4528approximation used elsewhere in libpng.
4529
4530WRITE APIS
4531
4532For write you must initialize a png_image structure to describe the image to
4533be written:
4534
4535 version: must be set to PNG_IMAGE_VERSION
4536 opaque: must be initialized to NULL
4537 width: image width in pixels
4538 height: image height in rows
4539 format: the format of the data you wish to write
4540 flags: set to 0 unless one of the defined flags applies; set
4541 PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB for color format images
4542 where the RGB values do not correspond to the colors in sRGB.
4543 colormap_entries: set to the number of entries in the color-map (0 to 256)
4544
4545 int png_image_write_to_file, (png_imagep image,
4546 const char *file, int convert_to_8bit, const void *buffer,
4547 png_int_32 row_stride, const void *colormap));
4548
4549 Write the image to the named file.
4550
4551 int png_image_write_to_stdio(png_imagep image, FILE *file,
4552 int convert_to_8_bit, const void *buffer,
4553 png_int_32 row_stride, const void *colormap)
4554
4555 Write the image to the given (FILE*).
4556
4557With all write APIs if image is in one of the linear formats with
4558(png_uint_16) data then setting convert_to_8_bit will cause the output to be
4559a (png_byte) PNG gamma encoded according to the sRGB specification, otherwise
4560a 16-bit linear encoded PNG file is written.
4561
4562With all APIs row_stride is handled as in the read APIs - it is the spacing
4563from one row to the next in component sized units (float) and if negative
4564indicates a bottom-up row layout in the buffer.
4565
4566Note that the write API does not support interlacing, sub-8-bit pixels,
4567and indexed (paletted) images.
4568
4569.SH VI. Modifying/Customizing libpng
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4570
4571There are two issues here. The first is changing how libpng does
4572standard things like memory allocation, input/output, and error handling.
4573The second deals with more complicated things like adding new chunks,
4574adding new transformations, and generally changing how libpng works.
4575Both of those are compile-time issues; that is, they are generally
4576determined at the time the code is written, and there is rarely a need
4577to provide the user with a means of changing them.
4578
4579Memory allocation, input/output, and error handling
4580
4581All of the memory allocation, input/output, and error handling in libpng
4582goes through callbacks that are user-settable. The default routines are
4583in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
4584these functions, call the appropriate png_set_*_fn() function.
4585
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]4586Memory allocation is done through the functions png_malloc(), png_calloc(),
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4587and png_free(). The png_malloc() and png_free() functions currently just
4588call the standard C functions and png_calloc() calls png_malloc() and then
4589clears the newly allocated memory to zero; note that png_calloc(png_ptr, size)
4590is not the same as the calloc(number, size) function provided by stdlib.h.
4591There is limited support for certain systems with segmented memory
4592architectures and the types of pointers declared by png.h match this; you
4593will have to use appropriate pointers in your application. Since it is
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]4594unlikely that the method of handling memory allocation on a platform
4595will change between applications, these functions must be modified in
4596the library at compile time. If you prefer to use a different method
4597of allocating and freeing data, you can use png_create_read_struct_2() or
4598png_create_write_struct_2() to register your own functions as described
4599above. These functions also provide a void pointer that can be retrieved
4600via
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4601
4602 mem_ptr=png_get_mem_ptr(png_ptr);
4603
4604Your replacement memory functions must have prototypes as follows:
4605
4606 png_voidp malloc_fn(png_structp png_ptr,
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4607 png_alloc_size_t size);
4608
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4609 void free_fn(png_structp png_ptr, png_voidp ptr);
4610
4611Your malloc_fn() must return NULL in case of failure. The png_malloc()
4612function will normally call png_error() if it receives a NULL from the
4613system memory allocator or from your replacement malloc_fn().
4614
4615Your free_fn() will never be called with a NULL ptr, since libpng's
4616png_free() checks for NULL before calling free_fn().
4617
4618Input/Output in libpng is done through png_read() and png_write(),
4619which currently just call fread() and fwrite(). The FILE * is stored in
4620png_struct and is initialized via png_init_io(). If you wish to change
4621the method of I/O, the library supplies callbacks that you can set
4622through the function png_set_read_fn() and png_set_write_fn() at run
4623time, instead of calling the png_init_io() function. These functions
4624also provide a void pointer that can be retrieved via the function
4625png_get_io_ptr(). For example:
4626
4627 png_set_read_fn(png_structp read_ptr,
4628 voidp read_io_ptr, png_rw_ptr read_data_fn)
4629
4630 png_set_write_fn(png_structp write_ptr,
4631 voidp write_io_ptr, png_rw_ptr write_data_fn,
4632 png_flush_ptr output_flush_fn);
4633
4634 voidp read_io_ptr = png_get_io_ptr(read_ptr);
4635 voidp write_io_ptr = png_get_io_ptr(write_ptr);
4636
4637The replacement I/O functions must have prototypes as follows:
4638
4639 void user_read_data(png_structp png_ptr,
4640 png_bytep data, png_size_t length);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4641
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4642 void user_write_data(png_structp png_ptr,
4643 png_bytep data, png_size_t length);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4644
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4645 void user_flush_data(png_structp png_ptr);
4646
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]4647The user_read_data() function is responsible for detecting and
4648handling end-of-data errors.
4649
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4650Supplying NULL for the read, write, or flush functions sets them back
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]4651to using the default C stream functions, which expect the io_ptr to
4652point to a standard *FILE structure. It is probably a mistake
4653to use NULL for one of write_data_fn and output_flush_fn but not both
4654of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
4655It is an error to read from a write stream, and vice versa.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4656
4657Error handling in libpng is done through png_error() and png_warning().
4658Errors handled through png_error() are fatal, meaning that png_error()
4659should never return to its caller. Currently, this is handled via
4660setjmp() and longjmp() (unless you have compiled libpng with
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4661PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
4662but you could change this to do things like exit() if you should wish,
4663as long as your function does not return.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4664
4665On non-fatal errors, png_warning() is called
4666to print a warning message, and then control returns to the calling code.
4667By default png_error() and png_warning() print a message on stderr via
4668fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
4669(because you don't want the messages) or PNG_NO_STDIO defined (because
4670fprintf() isn't available). If you wish to change the behavior of the error
4671functions, you will need to set up your own message callbacks. These
4672functions are normally supplied at the time that the png_struct is created.
4673It is also possible to redirect errors and warnings to your own replacement
4674functions after png_create_*_struct() has been called by calling:
4675
4676 png_set_error_fn(png_structp png_ptr,
4677 png_voidp error_ptr, png_error_ptr error_fn,
4678 png_error_ptr warning_fn);
4679
4680 png_voidp error_ptr = png_get_error_ptr(png_ptr);
4681
4682If NULL is supplied for either error_fn or warning_fn, then the libpng
4683default function will be used, calling fprintf() and/or longjmp() if a
4684problem is encountered. The replacement error functions should have
4685parameters as follows:
4686
4687 void user_error_fn(png_structp png_ptr,
4688 png_const_charp error_msg);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4689
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4690 void user_warning_fn(png_structp png_ptr,
4691 png_const_charp warning_msg);
4692
4693The motivation behind using setjmp() and longjmp() is the C++ throw and
4694catch exception handling methods. This makes the code much easier to write,
4695as there is no need to check every return code of every function call.
4696However, there are some uncertainties about the status of local variables
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]4697after a longjmp, so the user may want to be careful about doing anything
4698after setjmp returns non-zero besides returning itself. Consult your
4699compiler documentation for more details. For an alternative approach, you
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4700may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net),
4701which is illustrated in pngvalid.c and in contrib/visupng.
4702
4703Beginning in libpng-1.4.0, the png_set_benign_errors() API became available.
4704You can use this to handle certain errors (normally handled as errors)
4705as warnings.
4706
4707 png_set_benign_errors (png_ptr, int allowed);
4708
4709 allowed: 0: treat png_benign_error() as an error.
4710 1: treat png_benign_error() as a warning.
4711
4712As of libpng-1.6.0, the default condition is to treat benign errors as
4713warnings while reading and as errors while writing.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4714
4715.SS Custom chunks
4716
4717If you need to read or write custom chunks, you may need to get deeper
4718into the libpng code. The library now has mechanisms for storing
4719and writing chunks of unknown type; you can even declare callbacks
4720for custom chunks. However, this may not be good enough if the
4721library code itself needs to know about interactions between your
4722chunk and existing `intrinsic' chunks.
4723
4724If you need to write a new intrinsic chunk, first read the PNG
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]4725specification. Acquire a first level of understanding of how it works.
4726Pay particular attention to the sections that describe chunk names,
4727and look at how other chunks were designed, so you can do things
4728similarly. Second, check out the sections of libpng that read and
4729write chunks. Try to find a chunk that is similar to yours and use
4730it as a template. More details can be found in the comments inside
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4731the code. It is best to handle private or unknown chunks in a generic method,
4732via callback functions, instead of by modifying libpng functions. This
4733is illustrated in pngtest.c, which uses a callback function to handle a
4734private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
4735libpng.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4736
4737If you wish to write your own transformation for the data, look through
4738the part of the code that does the transformations, and check out some of
4739the simpler ones to get an idea of how they work. Try to find a similar
4740transformation to the one you want to add and copy off of it. More details
4741can be found in the comments inside the code itself.
4742
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4743.SS Configuring for 16-bit platforms
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4744
4745You will want to look into zconf.h to tell zlib (and thus libpng) that
4746it cannot allocate more then 64K at a time. Even if you can, the memory
4747won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
4748
4749.SS Configuring for DOS
4750
4751For DOS users who only have access to the lower 640K, you will
4752have to limit zlib's memory usage via a png_set_compression_mem_level()
4753call. See zlib.h or zconf.h in the zlib library for more information.
4754
4755.SS Configuring for Medium Model
4756
4757Libpng's support for medium model has been tested on most of the popular
4758compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
4759defined, and FAR gets defined to far in pngconf.h, and you should be
4760all set. Everything in the library (except for zlib's structure) is
4761expecting far data. You must use the typedefs with the p or pp on
4762the end for pointers (or at least look at them and be careful). Make
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4763note that the rows of data are defined as png_bytepp, which is
4764an "unsigned char far * far *".
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4765
4766.SS Configuring for gui/windowing platforms:
4767
4768You will need to write new error and warning functions that use the GUI
4769interface, as described previously, and set them to be the error and
4770warning functions at the time that png_create_*_struct() is called,
4771in order to have them available during the structure initialization.
4772They can be changed later via png_set_error_fn(). On some compilers,
4773you may also have to change the memory allocators (png_malloc, etc.).
4774
4775.SS Configuring for compiler xxx:
4776
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]4777All includes for libpng are in pngconf.h. If you need to add, change
4778or delete an include, this is the place to do it.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4779The includes that are not needed outside libpng are placed in pngpriv.h,
4780which is only used by the routines inside libpng itself.
4781The files in libpng proper only include pngpriv.h and png.h, which
4782%14%in turn includes pngconf.h.
4783in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h.
4784As of libpng-1.5.0, pngpriv.h also includes three other private header
4785files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material
4786that previously appeared in the public headers.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4787
4788.SS Configuring zlib:
4789
4790There are special functions to configure the compression. Perhaps the
4791most useful one changes the compression level, which currently uses
4792input compression values in the range 0 - 9. The library normally
4793uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
4794have shown that for a large majority of images, compression values in
4795the range 3-6 compress nearly as well as higher levels, and do so much
4796faster. For online applications it may be desirable to have maximum speed
4797(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
4798specify no compression (Z_NO_COMPRESSION = 0), but this would create
4799files larger than just storing the raw bitmap. You can specify the
4800compression level by calling:
4801
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4802 #include zlib.h
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4803 png_set_compression_level(png_ptr, level);
4804
4805Another useful one is to reduce the memory level used by the library.
4806The memory level defaults to 8, but it can be lowered if you are
4807short on memory (running DOS, for example, where you only have 640K).
4808Note that the memory level does have an effect on compression; among
4809other things, lower levels will result in sections of incompressible
4810data being emitted in smaller stored blocks, with a correspondingly
4811larger relative overhead of up to 15% in the worst case.
4812
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4813 #include zlib.h
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4814 png_set_compression_mem_level(png_ptr, level);
4815
4816The other functions are for configuring zlib. They are not recommended
4817for normal use and may result in writing an invalid PNG file. See
4818zlib.h for more information on what these mean.
4819
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4820 #include zlib.h
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4821 png_set_compression_strategy(png_ptr,
4822 strategy);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4823
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4824 png_set_compression_window_bits(png_ptr,
4825 window_bits);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4826
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4827 png_set_compression_method(png_ptr, method);
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4828
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4829 png_set_compression_buffer_size(png_ptr, size);
4830
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4831As of libpng version 1.5.4, additional APIs became
4832available to set these separately for non-IDAT
4833compressed chunks such as zTXt, iTXt, and iCCP:
4834
4835 #include zlib.h
4836 #if PNG_LIBPNG_VER >= 10504
4837 png_set_text_compression_level(png_ptr, level);
4838
4839 png_set_text_compression_mem_level(png_ptr, level);
4840
4841 png_set_text_compression_strategy(png_ptr,
4842 strategy);
4843
4844 png_set_text_compression_window_bits(png_ptr,
4845 window_bits);
4846
4847 png_set_text_compression_method(png_ptr, method);
4848 #endif
4849
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4850.SS Controlling row filtering
4851
4852If you want to control whether libpng uses filtering or not, which
4853filters are used, and how it goes about picking row filters, you
4854can call one of these functions. The selection and configuration
4855of row filters can have a significant impact on the size and
4856encoding speed and a somewhat lesser impact on the decoding speed
4857of an image. Filtering is enabled by default for RGB and grayscale
4858images (with and without alpha), but not for paletted images nor
4859for any images with bit depths less than 8 bits/pixel.
4860
4861The 'method' parameter sets the main filtering method, which is
4862currently only '0' in the PNG 1.2 specification. The 'filters'
4863parameter sets which filter(s), if any, should be used for each
4864scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
4865to turn filtering on and off, respectively.
4866
4867Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
4868PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
4869ORed together with '|' to specify one or more filters to use.
4870These filters are described in more detail in the PNG specification.
4871If you intend to change the filter type during the course of writing
4872the image, you should start with flags set for all of the filters
4873you intend to use so that libpng can initialize its internal
4874structures appropriately for all of the filter types. (Note that this
4875means the first row must always be adaptively filtered, because libpng
4876currently does not allocate the filter buffers until png_write_row()
4877is called for the first time.)
4878
4879 filters = PNG_FILTER_NONE | PNG_FILTER_SUB
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]4880 PNG_FILTER_UP | PNG_FILTER_AVG |
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4881 PNG_FILTER_PAETH | PNG_ALL_FILTERS;
4882
4883 png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
4884 filters);
4885 The second parameter can also be
4886 PNG_INTRAPIXEL_DIFFERENCING if you are
4887 writing a PNG to be embedded in a MNG
4888 datastream. This parameter must be the
4889 same as the value of filter_method used
4890 in png_set_IHDR().
4891
4892It is also possible to influence how libpng chooses from among the
4893available filters. This is done in one or both of two ways - by
4894telling it how important it is to keep the same filter for successive
4895rows, and by telling it the relative computational costs of the filters.
4896
4897 double weights[3] = {1.5, 1.3, 1.1},
4898 costs[PNG_FILTER_VALUE_LAST] =
4899 {1.0, 1.3, 1.3, 1.5, 1.7};
4900
4901 png_set_filter_heuristics(png_ptr,
4902 PNG_FILTER_HEURISTIC_WEIGHTED, 3,
4903 weights, costs);
4904
4905The weights are multiplying factors that indicate to libpng that the
4906row filter should be the same for successive rows unless another row filter
4907is that many times better than the previous filter. In the above example,
4908if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
4909"sum of absolute differences" 1.5 x 1.3 times higher than other filters
4910and still be chosen, while the NONE filter could have a sum 1.1 times
4911higher than other filters and still be chosen. Unspecified weights are
4912taken to be 1.0, and the specified weights should probably be declining
4913like those above in order to emphasize recent filters over older filters.
4914
4915The filter costs specify for each filter type a relative decoding cost
4916to be considered when selecting row filters. This means that filters
4917with higher costs are less likely to be chosen over filters with lower
4918costs, unless their "sum of absolute differences" is that much smaller.
4919The costs do not necessarily reflect the exact computational speeds of
4920the various filters, since this would unduly influence the final image
4921size.
4922
4923Note that the numbers above were invented purely for this example and
4924are given only to help explain the function usage. Little testing has
4925been done to find optimum values for either the costs or the weights.
4926
4927.SS Removing unwanted object code
4928
4929There are a bunch of #define's in pngconf.h that control what parts of
4930libpng are compiled. All the defines end in _SUPPORTED. If you are
4931never going to use a capability, you can change the #define to #undef
4932before recompiling libpng and save yourself code and data space, or
4933you can turn off individual capabilities with defines that begin with
4934PNG_NO_.
4935
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4936In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
4937
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4938You can also turn all of the transforms and ancillary chunk capabilities
4939off en masse with compiler directives that define
4940PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
4941or all four,
4942along with directives to turn on any of the capabilities that you do
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]4943want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
4944transformations but still leave the library fully capable of reading
4945and writing PNG files with all known public chunks. Use of the
4946PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
4947that is incapable of reading or writing ancillary chunks. If you are
4948not using the progressive reading capability, you can turn that off
4949with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
4950capability, which you'll still have).
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4951
4952All the reading and writing specific code are in separate files, so the
4953linker should only grab the files it needs. However, if you want to
4954make sure, or if you are building a stand alone library, all the
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4955reading files start with "pngr" and all the writing files start with "pngw".
4956The files that don't match either (like png.c, pngtrans.c, etc.)
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4957are used for both reading and writing, and always need to be included.
4958The progressive reader is in pngpread.c
4959
4960If you are creating or distributing a dynamically linked library (a .so
4961or DLL file), you should not remove or disable any parts of the library,
4962as this will cause applications linked with different versions of the
4963library to fail if they call functions not available in your library.
4964The size of the library itself should not be an issue, because only
4965those sections that are actually used will be loaded into memory.
4966
4967.SS Requesting debug printout
4968
4969The macro definition PNG_DEBUG can be used to request debugging
4970printout. Set it to an integer value in the range 0 to 3. Higher
4971numbers result in increasing amounts of debugging information. The
4972information is printed to the "stderr" file, unless another file
4973name is specified in the PNG_DEBUG_FILE macro definition.
4974
4975When PNG_DEBUG > 0, the following functions (macros) become available:
4976
4977 png_debug(level, message)
4978 png_debug1(level, message, p1)
4979 png_debug2(level, message, p1, p2)
4980
4981in which "level" is compared to PNG_DEBUG to decide whether to print
4982the message, "message" is the formatted string to be printed,
4983and p1 and p2 are parameters that are to be embedded in the string
4984according to printf-style formatting directives. For example,
4985
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4986 png_debug1(2, "foo=%d", foo);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4987
4988is expanded to
4989
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]4990 if (PNG_DEBUG > 2)
4991 fprintf(PNG_DEBUG_FILE, "foo=%d\en", foo);
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]4992
4993When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
4994can still use PNG_DEBUG to control your own debugging:
4995
4996 #ifdef PNG_DEBUG
4997 fprintf(stderr, ...
4998 #endif
4999
5000When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
5001having level = 0 will be printed. There aren't any such statements in
5002this version of libpng, but if you insert some they will be printed.
5003
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5004.SS Prepending a prefix to exported symbols
5005
5006Starting with libpng-1.6.0, you can configure libpng (when using the
5007"configure" script) to prefix all exported symbols by means of the
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5008configuration option "\-\-with\-libpng\-prefix=FOO_", where FOO_ can be any
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5009string beginning with a letter and containing only uppercase
5010and lowercase letters, digits, and the underscore (i.e., a C language
5011identifier). This creates a set of macros in pnglibconf.h, so this is
5012transparent to applications; their function calls get transformed by
5013the macros to use the modified names.
5014
5015.SH VII. MNG support
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5016
5017The MNG specification (available at http://www.libpng.org/pub/mng) allows
5018certain extensions to PNG for PNG images that are embedded in MNG datastreams.
5019Libpng can support some of these extensions. To enable them, use the
5020png_permit_mng_features() function:
5021
5022 feature_set = png_permit_mng_features(png_ptr, mask)
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5023
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5024 mask is a png_uint_32 containing the bitwise OR of the
5025 features you want to enable. These include
5026 PNG_FLAG_MNG_EMPTY_PLTE
5027 PNG_FLAG_MNG_FILTER_64
5028 PNG_ALL_MNG_FEATURES
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5029
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5030 feature_set is a png_uint_32 that is the bitwise AND of
5031 your mask with the set of MNG features that is
5032 supported by the version of libpng that you are using.
5033
5034It is an error to use this function when reading or writing a standalone
5035PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
5036in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
5037and the MHDR and MEND chunks. Libpng does not provide support for these
5038or any other MNG chunks; your application must provide its own support for
5039them. You may wish to consider using libmng (available at
5040http://www.libmng.com) instead.
5041
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5042.SH VIII. Changes to Libpng from version 0.88
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5043
5044It should be noted that versions of libpng later than 0.96 are not
5045distributed by the original libpng author, Guy Schalnat, nor by
5046Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
5047distributed versions 0.89 through 0.96, but rather by another member
5048of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
5049still alive and well, but they have moved on to other things.
5050
5051The old libpng functions png_read_init(), png_write_init(),
5052png_info_init(), png_read_destroy(), and png_write_destroy() have been
5053moved to PNG_INTERNAL in version 0.95 to discourage their use. These
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5054functions will be removed from libpng version 1.4.0.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5055
5056The preferred method of creating and initializing the libpng structures is
5057via the png_create_read_struct(), png_create_write_struct(), and
5058png_create_info_struct() because they isolate the size of the structures
5059from the application, allow version error checking, and also allow the
5060use of custom error handling routines during the initialization, which
5061the old functions do not. The functions png_read_destroy() and
5062png_write_destroy() do not actually free the memory that libpng
5063allocated for these structs, but just reset the data structures, so they
5064can be used instead of png_destroy_read_struct() and
5065png_destroy_write_struct() if you feel there is too much system overhead
5066allocating and freeing the png_struct for each image read.
5067
5068Setting the error callbacks via png_set_message_fn() before
5069png_read_init() as was suggested in libpng-0.88 is no longer supported
5070because this caused applications that do not use custom error functions
5071to fail if the png_ptr was not initialized to zero. It is still possible
5072to set the error callbacks AFTER png_read_init(), or to change them with
5073png_set_error_fn(), which is essentially the same function, but with a new
5074name to force compilation errors with applications that try to use the old
5075method.
5076
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5077Support for the sCAL, iCCP, iTXt, and sPLT chunks was added at libpng-1.0.6;
5078however, iTXt support was not enabled by default.
5079
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5080Starting with version 1.0.7, you can find out which version of the library
5081you are using at run-time:
5082
5083 png_uint_32 libpng_vn = png_access_version_number();
5084
5085The number libpng_vn is constructed from the major version, minor
5086version with leading zero, and release number with leading zero,
5087(e.g., libpng_vn for version 1.0.7 is 10007).
5088
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5089Note that this function does not take a png_ptr, so you can call it
5090before you've created one.
5091
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5092You can also check which version of png.h you used when compiling your
5093application:
5094
5095 png_uint_32 application_vn = PNG_LIBPNG_VER;
5096
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5097.SH IX. Changes to Libpng from version 1.0.x to 1.2.x
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5098
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5099Support for user memory management was enabled by default. To
5100accomplish this, the functions png_create_read_struct_2(),
5101png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
5102png_malloc_default(), and png_free_default() were added.
5103
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]5104Support for the iTXt chunk has been enabled by default as of
5105version 1.2.41.
5106
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5107Support for certain MNG features was enabled.
5108
5109Support for numbered error messages was added. However, we never got
5110around to actually numbering the error messages. The function
5111png_set_strip_error_numbers() was added (Note: the prototype for this
5112function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
5113builds of libpng-1.2.15. It was restored in libpng-1.2.36).
5114
5115The png_malloc_warn() function was added at libpng-1.2.3. This issues
5116a png_warning and returns NULL instead of aborting when it fails to
5117acquire the requested memory allocation.
5118
5119Support for setting user limits on image width and height was enabled
5120by default. The functions png_set_user_limits(), png_get_user_width_max(),
5121and png_get_user_height_max() were added at libpng-1.2.6.
5122
5123The png_set_add_alpha() function was added at libpng-1.2.7.
5124
5125The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
5126Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
5127tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
5128deprecated.
5129
5130A number of macro definitions in support of runtime selection of
5131assembler code features (especially Intel MMX code support) were
5132added at libpng-1.2.0:
5133
5134 PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
5135 PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
5136 PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
5137 PNG_ASM_FLAG_MMX_READ_INTERLACE
5138 PNG_ASM_FLAG_MMX_READ_FILTER_SUB
5139 PNG_ASM_FLAG_MMX_READ_FILTER_UP
5140 PNG_ASM_FLAG_MMX_READ_FILTER_AVG
5141 PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
5142 PNG_ASM_FLAGS_INITIALIZED
5143 PNG_MMX_READ_FLAGS
5144 PNG_MMX_FLAGS
5145 PNG_MMX_WRITE_FLAGS
5146 PNG_MMX_FLAGS
5147
5148We added the following functions in support of runtime
5149selection of assembler code features:
5150
5151 png_get_mmx_flagmask()
5152 png_set_mmx_thresholds()
5153 png_get_asm_flags()
5154 png_get_mmx_bitdepth_threshold()
5155 png_get_mmx_rowbytes_threshold()
5156 png_set_asm_flags()
5157
5158We replaced all of these functions with simple stubs in libpng-1.2.20,
5159when the Intel assembler code was removed due to a licensing issue.
5160
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]5161These macros are deprecated:
5162
5163 PNG_READ_TRANSFORMS_NOT_SUPPORTED
5164 PNG_PROGRESSIVE_READ_NOT_SUPPORTED
5165 PNG_NO_SEQUENTIAL_READ_SUPPORTED
5166 PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
5167 PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
5168 PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
5169
5170They have been replaced, respectively, by:
5171
5172 PNG_NO_READ_TRANSFORMS
5173 PNG_NO_PROGRESSIVE_READ
5174 PNG_NO_SEQUENTIAL_READ
5175 PNG_NO_WRITE_TRANSFORMS
5176 PNG_NO_READ_ANCILLARY_CHUNKS
5177 PNG_NO_WRITE_ANCILLARY_CHUNKS
5178
5179PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
5180deprecated since libpng-1.0.16 and libpng-1.2.6.
5181
5182The function
5183 png_check_sig(sig, num)
5184was replaced with
5185 !png_sig_cmp(sig, 0, num)
5186It has been deprecated since libpng-0.90.
5187
5188The function
5189 png_set_gray_1_2_4_to_8()
5190which also expands tRNS to alpha was replaced with
5191 png_set_expand_gray_1_2_4_to_8()
5192which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
5193
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5194.SH X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5195
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5196Private libpng prototypes and macro definitions were moved from
5197png.h and pngconf.h into a new pngpriv.h header file.
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]5198
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5199Functions png_set_benign_errors(), png_benign_error(), and
5200png_chunk_benign_error() were added.
5201
5202Support for setting the maximum amount of memory that the application
5203will allocate for reading chunks was added, as a security measure.
5204The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
5205were added to the library.
5206
5207We implemented support for I/O states by adding png_ptr member io_state
5208and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
5209
5210We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
5211input transforms.
5212
5213Checking for and reporting of errors in the IHDR chunk is more thorough.
5214
5215Support for global arrays was removed, to improve thread safety.
5216
5217Some obsolete/deprecated macros and functions have been removed.
5218
5219Typecasted NULL definitions such as
5220 #define png_voidp_NULL (png_voidp)NULL
5221were eliminated. If you used these in your application, just use
5222NULL instead.
5223
5224The png_struct and info_struct members "trans" and "trans_values" were
5225changed to "trans_alpha" and "trans_color", respectively.
5226
5227The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
5228were removed.
5229
5230The PNG_1_0_X and PNG_1_2_X macros were eliminated.
5231
5232The PNG_LEGACY_SUPPORTED macro was eliminated.
5233
5234Many WIN32_WCE #ifdefs were removed.
5235
5236The functions png_read_init(info_ptr), png_write_init(info_ptr),
5237png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
5238have been removed. They have been deprecated since libpng-0.95.
5239
5240The png_permit_empty_plte() was removed. It has been deprecated
5241since libpng-1.0.9. Use png_permit_mng_features() instead.
5242
5243We removed the obsolete stub functions png_get_mmx_flagmask(),
5244png_set_mmx_thresholds(), png_get_asm_flags(),
5245png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
5246png_set_asm_flags(), and png_mmx_supported()
5247
5248We removed the obsolete png_check_sig(), png_memcpy_check(), and
5249png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
5250and memset(), respectively.
5251
5252The function png_set_gray_1_2_4_to_8() was removed. It has been
5253deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
5254png_set_expand_gray_1_2_4_to_8() because the former function also
5255expanded any tRNS chunk to an alpha channel.
5256
5257Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
5258were added and are used by default instead of the corresponding
5259functions. Unfortunately,
5260from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5261function) incorrectly returned a value of type png_uint_32.
5262
5263We changed the prototype for png_malloc() from
5264 png_malloc(png_structp png_ptr, png_uint_32 size)
5265to
5266 png_malloc(png_structp png_ptr, png_alloc_size_t size)
5267
5268This also applies to the prototype for the user replacement malloc_fn().
5269
5270The png_calloc() function was added and is used in place of
5271of "png_malloc(); memset();" except in the case in png_read_png()
5272where the array consists of pointers; in this case a "for" loop is used
5273after the png_malloc() to set the pointers to NULL, to give robust.
5274behavior in case the application runs out of memory part-way through
5275the process.
5276
5277We changed the prototypes of png_get_compression_buffer_size() and
5278png_set_compression_buffer_size() to work with png_size_t instead of
5279png_uint_32.
5280
5281Support for numbered error messages was removed by default, since we
5282never got around to actually numbering the error messages. The function
5283png_set_strip_error_numbers() was removed from the library by default.
5284
5285The png_zalloc() and png_zfree() functions are no longer exported.
5286The png_zalloc() function no longer zeroes out the memory that it
5287allocates. Applications that called png_zalloc(png_ptr, number, size)
5288can call png_calloc(png_ptr, number*size) instead, and can call
5289png_free() instead of png_zfree().
5290
5291Support for dithering was disabled by default in libpng-1.4.0, because
5292it has not been well tested and doesn't actually "dither".
5293The code was not
5294removed, however, and could be enabled by building libpng with
5295PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5296was re-enabled, but the function was renamed png_set_quantize() to
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5297reflect more accurately what it actually does. At the same time,
5298the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
5299PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
5300was renamed to PNG_READ_QUANTIZE_SUPPORTED.
5301
5302We removed the trailing '.' from the warning and error messages.
5303
5304.SH XI. Changes to Libpng from version 1.4.x to 1.5.x
5305
5306From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
5307function) incorrectly returned a value of type png_uint_32.
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5308The incorrect macro was removed from libpng-1.4.5.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5309
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5310Checking for invalid palette index on write was added at libpng
53111.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
5312a benign error. This is enabled by default because this condition is an
5313error according to the PNG specification, Clause 11.3.2, but the error can
5314be ignored in each png_ptr with
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5315
5316 png_set_check_for_invalid_index(png_ptr, allowed);
5317
5318 allowed - one of
5319 0: disable benign error (accept the
5320 invalid data without warning).
5321 1: enable benign error (treat the
5322 invalid data as an error or a
5323 warning).
5324
5325If the error is ignored, or if png_benign_error() treats it as a warning,
5326any invalid pixels are decoded as opaque black by the decoder and written
5327as-is by the encoder.
5328
5329Retrieving the maximum palette index found was added at libpng-1.5.15.
5330This statement must appear after png_read_png() or png_read_image() while
5331reading, and after png_write_png() or png_write_image() while writing.
5332
5333 int max_palette = png_get_palette_max(png_ptr, info_ptr);
5334
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5335This will return the maximum palette index found in the image, or "\-1" if
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5336the palette was not checked, or "0" if no palette was found. Note that this
5337does not account for any palette index used by ancillary chunks such as the
5338bKGD chunk; you must check those separately to determine the maximum
5339palette index actually used.
5340
5341A. Changes that affect users of libpng
5342
5343There are no substantial API changes between the non-deprecated parts of
5344the 1.4.5 API and the 1.5.0 API; however, the ability to directly access
5345members of the main libpng control structures, png_struct and png_info,
5346deprecated in earlier versions of libpng, has been completely removed from
5347libpng 1.5.
5348
5349We no longer include zlib.h in png.h. The include statement has been moved
5350to pngstruct.h, where it is not accessible by applications. Applications that
5351need access to information in zlib.h will need to add the '#include "zlib.h"'
5352directive. It does not matter whether this is placed prior to or after
5353the '"#include png.h"' directive.
5354
5355The png_sprintf(), png_strcpy(), and png_strncpy() macros are no longer used
5356and were removed.
5357
5358We moved the png_strlen(), png_memcpy(), png_memset(), and png_memcmp()
5359macros into a private header file (pngpriv.h) that is not accessible to
5360applications.
5361
5362In png_get_iCCP, the type of "profile" was changed from png_charpp
5363to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
5364
5365There are changes of form in png.h, including new and changed macros to
5366declare parts of the API. Some API functions with arguments that are
5367pointers to data not modified within the function have been corrected to
5368declare these arguments with PNG_CONST.
5369
5370Much of the internal use of C macros to control the library build has also
5371changed and some of this is visible in the exported header files, in
5372particular the use of macros to control data and API elements visible
5373during application compilation may require significant revision to
5374application code. (It is extremely rare for an application to do this.)
5375
5376Any program that compiled against libpng 1.4 and did not use deprecated
5377features or access internal library structures should compile and work
5378against libpng 1.5, except for the change in the prototype for
5379png_get_iCCP() and png_set_iCCP() API functions mentioned above.
5380
5381libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
5382interlaced images. The macros return the number of rows and columns in
5383each pass and information that can be used to de-interlace and (if
5384absolutely necessary) interlace an image.
5385
5386libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
5387the application-provided png_longjmp_ptr on the internal, but application
5388initialized, longjmp buffer. It is provided as a convenience to avoid
5389the need to use the png_jmpbuf macro, which had the unnecessary side
5390effect of resetting the internal png_longjmp_ptr value.
5391
5392libpng 1.5.0 includes a complete fixed point API. By default this is
5393present along with the corresponding floating point API. In general the
5394fixed point API is faster and smaller than the floating point one because
5395the PNG file format used fixed point, not floating point. This applies
5396even if the library uses floating point in internal calculations. A new
5397macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
5398uses floating point arithmetic (the default) or fixed point arithmetic
5399internally for performance critical calculations such as gamma correction.
5400In some cases, the gamma calculations may produce slightly different
5401results. This has changed the results in png_rgb_to_gray and in alpha
5402composition (png_set_background for example). This applies even if the
5403original image was already linear (gamma == 1.0) and, therefore, it is
5404not necessary to linearize the image. This is because libpng has *not*
5405been changed to optimize that case correctly, yet.
5406
5407Fixed point support for the sCAL chunk comes with an important caveat;
5408the sCAL specification uses a decimal encoding of floating point values
5409and the accuracy of PNG fixed point values is insufficient for
5410representation of these values. Consequently a "string" API
5411(png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
5412arbitrary sCAL chunks in the absence of either the floating point API or
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5413internal floating point calculations. Starting with libpng-1.5.0, both
5414of these functions are present when PNG_sCAL_SUPPORTED is defined. Prior
5415to libpng-1.5.0, their presence also depended upon PNG_FIXED_POINT_SUPPORTED
5416being defined and PNG_FLOATING_POINT_SUPPORTED not being defined.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5417
5418Applications no longer need to include the optional distribution header
5419file pngusr.h or define the corresponding macros during application
5420build in order to see the correct variant of the libpng API. From 1.5.0
5421application code can check for the corresponding _SUPPORTED macro:
5422
5423#ifdef PNG_INCH_CONVERSIONS_SUPPORTED
5424 /* code that uses the inch conversion APIs. */
5425#endif
5426
5427This macro will only be defined if the inch conversion functions have been
5428compiled into libpng. The full set of macros, and whether or not support
5429has been compiled in, are available in the header file pnglibconf.h.
5430This header file is specific to the libpng build. Notice that prior to
54311.5.0 the _SUPPORTED macros would always have the default definition unless
5432reset by pngusr.h or by explicit settings on the compiler command line.
5433These settings may produce compiler warnings or errors in 1.5.0 because
5434of macro redefinition.
5435
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5436Applications can now choose whether to use these macros or to call the
5437corresponding function by defining PNG_USE_READ_MACROS or
5438PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5439only supported from 1.5.0; defining PNG_NO_USE_READ_MACROS prior to 1.5.0
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5440will lead to a link failure.
5441
5442Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
5443when compressing the IDAT data and textual data such as zTXt and iCCP.
5444In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
5445We added five png_set_text_*() functions for setting the parameters to
5446use with textual data.
5447
5448Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
5449option was off by default, and slightly inaccurate scaling occurred.
5450This option can no longer be turned off, and the choice of accurate
5451or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
5452API for accurate scaling or the old png_set_strip_16_to_8() API for simple
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5453chopping. In libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
5454macro became PNG_READ_SCALE_16_TO_8_SUPPORTED, and the PNG_READ_16_TO_8
5455macro became PNG_READ_STRIP_16_TO_8_SUPPORTED, to enable the two
5456png_set_*_16_to_8() functions separately.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5457
5458Prior to libpng-1.5.4, the png_set_user_limits() function could only be
5459used to reduce the width and height limits from the value of
5460PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
5461that it could be used to override them. Now this function will reduce or
5462increase the limits.
5463
5464Starting in libpng-1.5.10, the user limits can be set en masse with the
5465configuration option PNG_SAFE_LIMITS_SUPPORTED. If this option is enabled,
5466a set of "safe" limits is applied in pngpriv.h. These can be overridden by
5467application calls to png_set_user_limits(), png_set_user_chunk_cache_max(),
5468and/or png_set_user_malloc_max() that increase or decrease the limits. Also,
5469in libpng-1.5.10 the default width and height limits were increased
5470from 1,000,000 to 0x7ffffff (i.e., made unlimited). Therefore, the
5471limits are now
5472 default safe
5473 png_user_width_max 0x7fffffff 1,000,000
5474 png_user_height_max 0x7fffffff 1,000,000
5475 png_user_chunk_cache_max 0 (unlimited) 128
5476 png_user_chunk_malloc_max 0 (unlimited) 8,000,000
5477
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5478The png_set_option() function (and the "options" member of the png struct) was
5479added to libpng-1.5.15.
5480
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5481B. Changes to the build and configuration of libpng
5482
5483Details of internal changes to the library code can be found in the CHANGES
5484file and in the GIT repository logs. These will be of no concern to the vast
5485majority of library users or builders; however, the few who configure libpng
5486to a non-default feature set may need to change how this is done.
5487
5488There should be no need for library builders to alter build scripts if
5489these use the distributed build support - configure or the makefiles -
5490however, users of the makefiles may care to update their build scripts
5491to build pnglibconf.h where the corresponding makefile does not do so.
5492
5493Building libpng with a non-default configuration has changed completely.
5494The old method using pngusr.h should still work correctly even though the
5495way pngusr.h is used in the build has been changed; however, library
5496builders will probably want to examine the changes to take advantage of
5497new capabilities and to simplify their build system.
5498
5499B.1 Specific changes to library configuration capabilities
5500
5501The library now supports a complete fixed point implementation and can
5502thus be used on systems that have no floating point support or very
5503limited or slow support. Previously gamma correction, an essential part
5504of complete PNG support, required reasonably fast floating point.
5505
5506As part of this the choice of internal implementation has been made
5507independent of the choice of fixed versus floating point APIs and all the
5508missing fixed point APIs have been implemented.
5509
5510The exact mechanism used to control attributes of API functions has
5511changed. A single set of operating system independent macro definitions
5512is used and operating system specific directives are defined in
5513pnglibconf.h
5514
5515As part of this the mechanism used to choose procedure call standards on
5516those systems that allow a choice has been changed. At present this only
5517affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
5518running on Intel processors. As before, PNGAPI is defined where required
5519to control the exported API functions; however, two new macros, PNGCBAPI
5520and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
5521(PNGCAPI) for functions that must match a C library prototype (currently
5522only png_longjmp_ptr, which must match the C longjmp function.) The new
5523approach is documented in pngconf.h
5524
5525Despite these changes, libpng 1.5.0 only supports the native C function
5526calling standard on those platforms tested so far (__cdecl on Microsoft
5527Windows). This is because the support requirements for alternative
5528calling conventions seem to no longer exist. Developers who find it
5529necessary to set PNG_API_RULE to 1 should advise the mailing list
5530(png-mng-implement) of this and library builders who use Openwatcom and
5531therefore set PNG_API_RULE to 2 should also contact the mailing list.
5532
5533A new test program, pngvalid, is provided in addition to pngtest.
5534pngvalid validates the arithmetic accuracy of the gamma correction
5535calculations and includes a number of validations of the file format.
5536A subset of the full range of tests is run when "make check" is done
5537(in the 'configure' build.) pngvalid also allows total allocated memory
5538usage to be evaluated and performs additional memory overwrite validation.
5539
5540Many changes to individual feature macros have been made. The following
5541are the changes most likely to be noticed by library builders who
5542configure libpng:
5543
55441) All feature macros now have consistent naming:
5545
5546#define PNG_NO_feature turns the feature off
5547#define PNG_feature_SUPPORTED turns the feature on
5548
5549pnglibconf.h contains one line for each feature macro which is either:
5550
5551#define PNG_feature_SUPPORTED
5552
5553if the feature is supported or:
5554
5555/*#undef PNG_feature_SUPPORTED*/
5556
5557if it is not. Library code consistently checks for the 'SUPPORTED' macro.
5558It does not, and libpng applications should not, check for the 'NO' macro
5559which will not normally be defined even if the feature is not supported.
5560The 'NO' macros are only used internally for setting or not setting the
5561corresponding 'SUPPORTED' macros.
5562
5563Compatibility with the old names is provided as follows:
5564
5565PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
5566
5567And the following definitions disable the corresponding feature:
5568
5569PNG_SETJMP_NOT_SUPPORTED disables SETJMP
5570PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
5571PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
5572PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
5573PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
5574PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
5575
5576Library builders should remove use of the above, inconsistent, names.
5577
55782) Warning and error message formatting was previously conditional on
5579the STDIO feature. The library has been changed to use the
5580CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
5581the library no longer uses the printf(3) functions, even though the
5582default read/write implementations use (FILE) style stdio.h functions.
5583
55843) Three feature macros now control the fixed/floating point decisions:
5585
5586PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
5587
5588PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
5589practice these are normally required internally anyway (because the PNG
5590file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
5591merely stops the function from being exported.
5592
5593PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
5594point implementation or the fixed point one. Typically the fixed point
5595implementation is larger and slower than the floating point implementation
5596on a system that supports floating point; however, it may be faster on a
5597system which lacks floating point hardware and therefore uses a software
5598emulation.
5599
56004) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
5601functions to read and write ints to be disabled independently of
5602PNG_USE_READ_MACROS, which allows libpng to be built with the functions
5603even though the default is to use the macros - this allows applications
5604to choose at app buildtime whether or not to use macros (previously
5605impossible because the functions weren't in the default build.)
5606
5607B.2 Changes to the configuration mechanism
5608
5609Prior to libpng-1.5.0 library builders who needed to configure libpng
5610had either to modify the exported pngconf.h header file to add system
5611specific configuration or had to write feature selection macros into
5612pngusr.h and cause this to be included into pngconf.h by defining
5613PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
5614application built without PNG_USER_CONFIG defined would see the
5615unmodified, default, libpng API and thus would probably fail to link.
5616
5617These mechanisms still work in the configure build and in any makefile
5618build that builds pnglibconf.h, although the feature selection macros
5619have changed somewhat as described above. In 1.5.0, however, pngusr.h is
5620processed only once, when the exported header file pnglibconf.h is built.
5621pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the
5622build of pnglibconf.h and it is never included in an application build.
5623
5624The rarely used alternative of adding a list of feature macros to the
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5625CPPFLAGS setting in the build also still works; however, the macros will be
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5626copied to pnglibconf.h and this may produce macro redefinition warnings
5627when the individual C files are compiled.
5628
5629All configuration now only works if pnglibconf.h is built from
5630scripts/pnglibconf.dfa. This requires the program awk. Brian Kernighan
5631(the original author of awk) maintains C source code of that awk and this
5632and all known later implementations (often called by subtly different
5633names - nawk and gawk for example) are adequate to build pnglibconf.h.
5634The Sun Microsystems (now Oracle) program 'awk' is an earlier version
5635and does not work; this may also apply to other systems that have a
5636functioning awk called 'nawk'.
5637
5638Configuration options are now documented in scripts/pnglibconf.dfa. This
5639file also includes dependency information that ensures a configuration is
5640consistent; that is, if a feature is switched off dependent features are
5641also removed. As a recommended alternative to using feature macros in
5642pngusr.h a system builder may also define equivalent options in pngusr.dfa
5643(or, indeed, any file) and add that to the configuration by setting
5644DFA_XTRA to the file name. The makefiles in contrib/pngminim illustrate
5645how to do this, and a case where pngusr.h is still required.
5646
5647.SH XII. Changes to Libpng from version 1.5.x to 1.6.x
5648
5649A "simplified API" has been added (see documentation in png.h and a simple
5650example in contrib/examples/pngtopng.c). The new publicly visible API
5651includes the following:
5652
5653 macros:
5654 PNG_FORMAT_*
5655 PNG_IMAGE_*
5656 structures:
5657 png_control
5658 png_image
5659 read functions
5660 png_image_begin_read_from_file()
5661 png_image_begin_read_from_stdio()
5662 png_image_begin_read_from_memory()
5663 png_image_finish_read()
5664 png_image_free()
5665 write functions
5666 png_image_write_to_file()
5667 png_image_write_to_stdio()
5668
5669Starting with libpng-1.6.0, you can configure libpng to prefix all exported
5670symbols, using the PNG_PREFIX macro.
5671
5672We no longer include string.h in png.h. The include statement has been moved
5673to pngpriv.h, where it is not accessible by applications. Applications that
5674need access to information in string.h must add an '#include <string.h>'
5675directive. It does not matter whether this is placed prior to or after
5676the '#include "png.h"' directive.
5677
5678The following API are now DEPRECATED:
5679 png_info_init_3()
5680 png_convert_to_rfc1123() which has been replaced
5681 with png_convert_to_rfc1123_buffer()
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5682 png_malloc_default()
5683 png_free_default()
5684 png_reset_zstream()
5685
5686The following have been removed:
5687 png_get_io_chunk_name(), which has been replaced
5688 with png_get_io_chunk_type(). The new
5689 function returns a 32-bit integer instead of
5690 a string.
5691 The png_sizeof(), png_strlen(), png_memcpy(), png_memcmp(), and
5692 png_memset() macros are no longer used in the libpng sources and
5693 have been removed. These had already been made invisible to applications
5694 (i.e., defined in the private pngpriv.h header file) since libpng-1.5.0.
5695
5696The signatures of many exported functions were changed, such that
5697 png_structp became png_structrp or png_const_structrp
5698 png_infop became png_inforp or png_const_inforp
5699where "rp" indicates a "restricted pointer".
5700
5701Error detection in some chunks has improved; in particular the iCCP chunk
5702reader now does pretty complete validation of the basic format. Some bad
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5703profiles that were previously accepted are now accepted with a warning or
5704rejected, depending upon the png_set_benign_errors() setting, in particular the
5705very old broken Microsoft/HP 3144-byte sRGB profile. The PNG spec requirement
5706that only grayscale profiles may appear in images with color type 0 or 4 and
5707that even if the image only contains gray pixels, only RGB profiles may appear
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5708in images with color type 2, 3, or 6, is now enforced. The sRGB chunk
5709is allowed to appear in images with any color type.
5710
5711Prior to libpng-1.6.0 a warning would be issued if the iTXt chunk contained
5712an empty language field or an empty translated keyword. Both of these
5713are allowed by the PNG specification, so these warnings are no longer issued.
5714
5715The library now issues an error if the application attempts to set a
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5716transform after it calls png_read_update_info() or if it attempts to call
5717both png_read_update_info() and png_start_read_image() or to call either
5718of them more than once.
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5719
5720The default condition for benign_errors is now to treat benign errors as
5721warnings while reading and as errors while writing.
5722
5723The library now issues a warning if both background processing and RGB to
5724gray are used when gamma correction happens. As with previous versions of
5725the library the results are numerically very incorrect in this case.
5726
5727There are some minor arithmetic changes in some transforms such as
5728png_set_background(), that might be detected by certain regression tests.
5729
5730Unknown chunk handling has been improved internally, without any API change.
5731This adds more correct option control of the unknown handling, corrects
5732a pre-existing bug where the per-chunk 'keep' setting is ignored, and makes
5733it possible to skip IDAT chunks in the sequential reader.
5734
5735The machine-generated configure files are no longer included in branches
5736libpng16 and later of the GIT repository. They continue to be included
5737in the tarball releases, however.
5738
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5739Libpng-1.6.0 through 1.6.2 used the CMF bytes at the beginning of the IDAT
5740stream to set the size of the sliding window for reading instead of using the
5741default 32-kbyte sliding window size. It was discovered that there are
5742hundreds of PNG files in the wild that have incorrect CMF bytes that caused
5743libpng to issue a "too far back" error and reject the file. Libpng-1.6.3 and
5744later calculate their own safe CMF from the image dimensions, provide a way
5745to revert to the libpng-1.5.x behavior (ignoring the CMF bytes and using a
574632-kbyte sliding window), by using
5747
5748 png_set_option(png_ptr, PNG_MAXIMUM_INFLATE_WINDOW,
5749 PNG_OPTION_ON);
5750
5751and provide a tool (contrib/tools/pngfix) for optimizing the CMF bytes
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5752correctly.
5753
5754Libpng-1.6.0 and libpng-1.6.1 wrote uncompressed iTXt chunks with the wrong
5755length, which resulted in PNG files that cannot be read beyond the bad iTXt
5756chunk. This error was fixed in libpng-1.6.3, and a tool (called
5757contrib/tools/png-fix-itxt) has been added to the libpng distribution.
5758
5759.SH XIII. Detecting libpng
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5760
5761The png_get_io_ptr() function has been present since libpng-0.88, has never
5762changed, and is unaffected by conditional compilation macros. It is the
5763best choice for use in configure scripts for detecting the presence of any
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]5764libpng version since 0.88. In an autoconf "configure.in" you could use
5765
5766 AC_CHECK_LIB(png, png_get_io_ptr, ...
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5767
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5768.SH XV. Source code repository
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5769
5770Since about February 2009, version 1.2.34, libpng has been under "git" source
5771control. The git repository was built from old libpng-x.y.z.tar.gz files
5772going back to version 0.70. You can access the git repository (read only)
5773at
5774
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5775 git://git.code.sf.net/p/libpng/code
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5776
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5777or you can browse it with a web browser by selecting the "code" button at
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5778
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5779 https://sourceforge.net/projects/libpng
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5780
5781Patches can be sent to glennrp at users.sourceforge.net or to
5782png-mng-implement at lists.sourceforge.net or you can upload them to
5783the libpng bug tracker at
5784
5785 http://libpng.sourceforge.net
5786
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5787We also accept patches built from the tar or zip distributions, and
5788simple verbal discriptions of bug fixes, reported either to the
5789SourceForge bug tracker, to the png-mng-implement at lists.sf.net
5790mailing list, or directly to glennrp.
5791
5792.SH XV. Coding style
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5793
5794Our coding style is similar to the "Allman" style, with curly
5795braces on separate lines:
5796
5797 if (condition)
5798 {
5799 action;
5800 }
5801
5802 else if (another condition)
5803 {
5804 another action;
5805 }
5806
5807The braces can be omitted from simple one-line actions:
5808
5809 if (condition)
5810 return (0);
5811
5812We use 3-space indentation, except for continued statements which
5813are usually indented the same as the first line of the statement
5814plus four more spaces.
5815
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]5816For macro definitions we use 2-space indentation, always leaving the "#"
5817in the first column.
5818
5819 #ifndef PNG_NO_FEATURE
5820 # ifndef PNG_FEATURE_SUPPORTED
5821 # define PNG_FEATURE_SUPPORTED
5822 # endif
5823 #endif
5824
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5825Comments appear with the leading "/*" at the same indentation as
5826the statement that follows the comment:
5827
5828 /* Single-line comment */
5829 statement;
5830
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5831 /* This is a multiple-line
5832 * comment.
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5833 */
5834 statement;
5835
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5836Very short comments can be placed after the end of the statement
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5837to which they pertain:
5838
5839 statement; /* comment */
5840
5841We don't use C++ style ("//") comments. We have, however,
5842used them in the past in some now-abandoned MMX assembler
5843code.
5844
5845Functions and their curly braces are not indented, and
5846exported functions are marked with PNGAPI:
5847
5848 /* This is a public function that is visible to
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5849 * application programmers. It does thus-and-so.
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5850 */
5851 void PNGAPI
5852 png_exported_function(png_ptr, png_info, foo)
5853 {
5854 body;
5855 }
5856
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5857The return type and decorations are placed on a separate line
5858ahead of the function name, as illustrated above.
5859
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]5860The prototypes for all exported functions appear in png.h,
5861above the comment that says
5862
5863 /* Maintainer: Put new public prototypes here ... */
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5864
5865We mark all non-exported functions with "/* PRIVATE */"":
5866
5867 void /* PRIVATE */
5868 png_non_exported_function(png_ptr, png_info, foo)
5869 {
5870 body;
5871 }
5872
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]5873The prototypes for non-exported functions (except for those in
5874pngtest) appear in
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5875pngpriv.h
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]5876above the comment that says
5877
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5878 /* Maintainer: Put new private prototypes here ^ */
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5879
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5880We put a space after the "sizeof" operator and we omit the
5881optional parentheses around its argument when the argument
5882is an expression, not a type name, and we always enclose the
5883sizeof operator, with its argument, in parentheses:
5884
5885 (sizeof (png_uint_32))
5886 (sizeof array)
5887
5888Prior to libpng-1.6.0 we used a "png_sizeof()" macro, formatted as
5889though it were a function.
5890
5891To avoid polluting the global namespace, the names of all exported
5892functions and variables begin with "png_", and all publicly visible C
5893preprocessor macros begin with "PNG". We request that applications that
5894use libpng *not* begin any of their own symbols with either of these strings.
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5895
5896We put a space after each comma and after each semicolon
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5897in "for" statements, and we put spaces before and after each
5898C binary operator and after "for" or "while", and before
5899"?". We don't put a space between a typecast and the expression
5900being cast, nor do we put one between a function name and the
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5901left parenthesis that follows it:
5902
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5903 for (i = 2; i > 0; \-\-i)
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]5904 y[i] = a(x) + (int)b;
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5905
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5906We prefer #ifdef and #ifndef to #if defined() and #if !defined()
5907when there is only one macro being tested. We always use parentheses
5908with "defined".
5909
5910We prefer to express integers that are used as bit masks in hex format,
5911with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
5912
5913We prefer to use underscores in variable names rather than camelCase, except
5914for a few type names that we inherit from zlib.h.
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5915
Patrick Scott5f6bd842010-06-28 16:55:16 -0400[diff] [blame]5916We do not use the TAB character for indentation in the C sources.
5917
5918Lines do not exceed 80 characters.
5919
5920Other rules can be inferred by inspecting the libpng source.
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5921
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5922.SH XVI. Y2K Compliance in libpng
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]5923
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5924March 6, 2014
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5925
5926Since the PNG Development group is an ad-hoc body, we can't make
5927an official declaration.
5928
5929This is your unofficial assurance that libpng from version 0.71 and
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]5930upward through 1.6.10 are Y2K compliant. It is my belief that earlier
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5931versions were also Y2K compliant.
5932
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5933Libpng only has two year fields. One is a 2-byte unsigned integer
5934that will hold years up to 65535. The other, which is deprecated,
5935holds the date in text format, and will hold years up to 9999.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5936
5937The integer is
5938 "png_uint_16 year" in png_time_struct.
5939
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]5940The string is
5941 "char time_buffer[29]" in png_struct. This is no longer used
5942in libpng-1.6.x and will be removed from libpng-1.7.0.
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]5943
5944There are seven time-related functions:
5945
5946 png_convert_to_rfc_1123() in png.c
5947 (formerly png_convert_to_rfc_1152() in error)
5948 png_convert_from_struct_tm() in pngwrite.c, called
5949 in pngwrite.c
5950 png_convert_from_time_t() in pngwrite.c
5951 png_get_tIME() in pngget.c
5952 png_handle_tIME() in pngrutil.c, called in pngread.c
5953 png_set_tIME() in pngset.c
5954 png_write_tIME() in pngwutil.c, called in pngwrite.c
5955
5956All appear to handle dates properly in a Y2K environment. The
5957png_convert_from_time_t() function calls gmtime() to convert from system
5958clock time, which returns (year - 1900), which we properly convert to
5959the full 4-digit year. There is a possibility that applications using
5960libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
5961function, or that they are incorrectly passing only a 2-digit year
5962instead of "year - 1900" into the png_convert_from_struct_tm() function,
5963but this is not under our control. The libpng documentation has always
5964stated that it works with 4-digit years, and the APIs have been
5965documented as such.
5966
5967The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
5968integer to hold the year, and can hold years as large as 65535.
5969
5970zlib, upon which libpng depends, is also Y2K compliant. It contains
5971no date-related code.
5972
5973
5974 Glenn Randers-Pehrson
5975 libpng maintainer
5976 PNG Development Group
5977
5978.SH NOTE
5979
5980Note about libpng version numbers:
5981
5982Due to various miscommunications, unforeseen code incompatibilities
5983and occasional factors outside the authors' control, version numbering
5984on the library has not always been consistent and straightforward.
5985The following table summarizes matters since version 0.89c, which was
5986the first widely used release:
5987
5988 source png.h png.h shared-lib
5989 version string int version
5990 ------- ------ ----- ----------
5991 0.89c ("beta 3") 0.89 89 1.0.89
5992 0.90 ("beta 4") 0.90 90 0.90
5993 0.95 ("beta 5") 0.95 95 0.95
5994 0.96 ("beta 6") 0.96 96 0.96
5995 0.97b ("beta 7") 1.00.97 97 1.0.1
5996 0.97c 0.97 97 2.0.97
5997 0.98 0.98 98 2.0.98
5998 0.99 0.99 98 2.0.99
5999 0.99a-m 0.99 99 2.0.99
6000 1.00 1.00 100 2.1.0
6001 1.0.0 1.0.0 100 2.1.0
6002 1.0.0 (from here on, the 100 2.1.0
6003 1.0.1 png.h string is 10001 2.1.0
6004 1.0.1a-e identical to the 10002 from here on, the
6005 1.0.2 source version) 10002 shared library is 2.V
6006 1.0.2a-b 10003 where V is the source
6007 1.0.1 10001 code version except as
6008 1.0.1a-e 10002 2.1.0.1a-e noted.
6009 1.0.2 10002 2.1.0.2
6010 1.0.2a-b 10003 2.1.0.2a-b
6011 1.0.3 10003 2.1.0.3
6012 1.0.3a-d 10004 2.1.0.3a-d
6013 1.0.4 10004 2.1.0.4
6014 1.0.4a-f 10005 2.1.0.4a-f
6015 1.0.5 (+ 2 patches) 10005 2.1.0.5
6016 1.0.5a-d 10006 2.1.0.5a-d
6017 1.0.5e-r 10100 2.1.0.5e-r
6018 1.0.5s-v 10006 2.1.0.5s-v
6019 1.0.6 (+ 3 patches) 10006 2.1.0.6
6020 1.0.6d-g 10007 2.1.0.6d-g
6021 1.0.6h 10007 10.6h
6022 1.0.6i 10007 10.6i
6023 1.0.6j 10007 2.1.0.6j
6024 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
6025 1.0.7beta15-18 1 10007 2.1.0.7beta15-18
6026 1.0.7rc1-2 1 10007 2.1.0.7rc1-2
6027 1.0.7 1 10007 2.1.0.7
6028 1.0.8beta1-4 1 10008 2.1.0.8beta1-4
6029 1.0.8rc1 1 10008 2.1.0.8rc1
6030 1.0.8 1 10008 2.1.0.8
6031 1.0.9beta1-6 1 10009 2.1.0.9beta1-6
6032 1.0.9rc1 1 10009 2.1.0.9rc1
6033 1.0.9beta7-10 1 10009 2.1.0.9beta7-10
6034 1.0.9rc2 1 10009 2.1.0.9rc2
6035 1.0.9 1 10009 2.1.0.9
6036 1.0.10beta1 1 10010 2.1.0.10beta1
6037 1.0.10rc1 1 10010 2.1.0.10rc1
6038 1.0.10 1 10010 2.1.0.10
6039 1.0.11beta1-3 1 10011 2.1.0.11beta1-3
6040 1.0.11rc1 1 10011 2.1.0.11rc1
6041 1.0.11 1 10011 2.1.0.11
6042 1.0.12beta1-2 2 10012 2.1.0.12beta1-2
6043 1.0.12rc1 2 10012 2.1.0.12rc1
6044 1.0.12 2 10012 2.1.0.12
6045 1.1.0a-f - 10100 2.1.1.0a-f abandoned
6046 1.2.0beta1-2 2 10200 2.1.2.0beta1-2
6047 1.2.0beta3-5 3 10200 3.1.2.0beta3-5
6048 1.2.0rc1 3 10200 3.1.2.0rc1
6049 1.2.0 3 10200 3.1.2.0
6050 1.2.1beta-4 3 10201 3.1.2.1beta1-4
6051 1.2.1rc1-2 3 10201 3.1.2.1rc1-2
6052 1.2.1 3 10201 3.1.2.1
6053 1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
6054 1.0.13beta1 10 10013 10.so.0.1.0.13beta1
6055 1.0.13rc1 10 10013 10.so.0.1.0.13rc1
6056 1.2.2rc1 12 10202 12.so.0.1.2.2rc1
6057 1.0.13 10 10013 10.so.0.1.0.13
6058 1.2.2 12 10202 12.so.0.1.2.2
6059 1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
6060 1.2.3 12 10203 12.so.0.1.2.3
6061 1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
6062 1.2.4rc1 13 10204 12.so.0.1.2.4rc1
6063 1.0.14 10 10014 10.so.0.1.0.14
6064 1.2.4 13 10204 12.so.0.1.2.4
6065 1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
6066 1.0.15rc1 10 10015 10.so.0.1.0.15rc1
6067 1.0.15 10 10015 10.so.0.1.0.15
6068 1.2.5 13 10205 12.so.0.1.2.5
6069 1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
6070 1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
6071 1.0.16 10 10016 10.so.0.1.0.16
6072 1.2.6 13 10206 12.so.0.1.2.6
6073 1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6074 1.0.17rc1 10 10017 12.so.0.1.0.17rc1
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6075 1.2.7rc1 13 10207 12.so.0.1.2.7rc1
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6076 1.0.17 10 10017 12.so.0.1.0.17
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6077 1.2.7 13 10207 12.so.0.1.2.7
6078 1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6079 1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6080 1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6081 1.0.18 10 10018 12.so.0.1.0.18
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6082 1.2.8 13 10208 12.so.0.1.2.8
6083 1.2.9beta1-3 13 10209 12.so.0.1.2.9beta1-3
6084 1.2.9beta4-11 13 10209 12.so.0.9[.0]
6085 1.2.9rc1 13 10209 12.so.0.9[.0]
6086 1.2.9 13 10209 12.so.0.9[.0]
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6087 1.2.10beta1-7 13 10210 12.so.0.10[.0]
6088 1.2.10rc1-2 13 10210 12.so.0.10[.0]
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6089 1.2.10 13 10210 12.so.0.10[.0]
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6090 1.4.0beta1-6 14 10400 14.so.0.0[.0]
6091 1.2.11beta1-4 13 10210 12.so.0.11[.0]
6092 1.4.0beta7-8 14 10400 14.so.0.0[.0]
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6093 1.2.11 13 10211 12.so.0.11[.0]
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6094 1.2.12 13 10212 12.so.0.12[.0]
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6095 1.4.0beta9-14 14 10400 14.so.0.0[.0]
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6096 1.2.13 13 10213 12.so.0.13[.0]
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6097 1.4.0beta15-36 14 10400 14.so.0.0[.0]
6098 1.4.0beta37-87 14 10400 14.so.14.0[.0]
6099 1.4.0rc01 14 10400 14.so.14.0[.0]
6100 1.4.0beta88-109 14 10400 14.so.14.0[.0]
6101 1.4.0rc02-08 14 10400 14.so.14.0[.0]
6102 1.4.0 14 10400 14.so.14.0[.0]
6103 1.4.1beta01-03 14 10401 14.so.14.1[.0]
6104 1.4.1rc01 14 10401 14.so.14.1[.0]
6105 1.4.1beta04-12 14 10401 14.so.14.1[.0]
6106 1.4.1 14 10401 14.so.14.1[.0]
6107 1.4.2 14 10402 14.so.14.2[.0]
6108 1.4.3 14 10403 14.so.14.3[.0]
6109 1.4.4 14 10404 14.so.14.4[.0]
6110 1.5.0beta01-58 15 10500 15.so.15.0[.0]
6111 1.5.0rc01-07 15 10500 15.so.15.0[.0]
6112 1.5.0 15 10500 15.so.15.0[.0]
6113 1.5.1beta01-11 15 10501 15.so.15.1[.0]
6114 1.5.1rc01-02 15 10501 15.so.15.1[.0]
6115 1.5.1 15 10501 15.so.15.1[.0]
6116 1.5.2beta01-03 15 10502 15.so.15.2[.0]
6117 1.5.2rc01-03 15 10502 15.so.15.2[.0]
6118 1.5.2 15 10502 15.so.15.2[.0]
6119 1.5.3beta01-10 15 10503 15.so.15.3[.0]
6120 1.5.3rc01-02 15 10503 15.so.15.3[.0]
6121 1.5.3beta11 15 10503 15.so.15.3[.0]
6122 1.5.3 [omitted]
6123 1.5.4beta01-08 15 10504 15.so.15.4[.0]
6124 1.5.4rc01 15 10504 15.so.15.4[.0]
6125 1.5.4 15 10504 15.so.15.4[.0]
6126 1.5.5beta01-08 15 10505 15.so.15.5[.0]
6127 1.5.5rc01 15 10505 15.so.15.5[.0]
6128 1.5.5 15 10505 15.so.15.5[.0]
6129 1.5.6beta01-07 15 10506 15.so.15.6[.0]
6130 1.5.6rc01-03 15 10506 15.so.15.6[.0]
6131 1.5.6 15 10506 15.so.15.6[.0]
6132 1.5.7beta01-05 15 10507 15.so.15.7[.0]
6133 1.5.7rc01-03 15 10507 15.so.15.7[.0]
6134 1.5.7 15 10507 15.so.15.7[.0]
6135 1.6.0beta01-40 16 10600 16.so.16.0[.0]
6136 1.6.0rc01-08 16 10600 16.so.16.0[.0]
6137 1.6.0 16 10600 16.so.16.0[.0]
6138 1.6.1beta01-09 16 10601 16.so.16.1[.0]
6139 1.6.1rc01 16 10601 16.so.16.1[.0]
6140 1.6.1 16 10601 16.so.16.1[.0]
6141 1.6.2beta01 16 10602 16.so.16.2[.0]
6142 1.6.2rc01-06 16 10602 16.so.16.2[.0]
6143 1.6.2 16 10602 16.so.16.2[.0]
6144 1.6.3beta01-11 16 10603 16.so.16.3[.0]
6145 1.6.3rc01 16 10603 16.so.16.3[.0]
6146 1.6.3 16 10603 16.so.16.3[.0]
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]6147 1.6.4beta01-02 16 10604 16.so.16.4[.0]
6148 1.6.4rc01 16 10604 16.so.16.4[.0]
6149 1.6.4 16 10604 16.so.16.4[.0]
6150 1.6.5 16 10605 16.so.16.5[.0]
6151 1.6.6 16 10606 16.so.16.6[.0]
6152 1.6.7beta01-04 16 10607 16.so.16.7[.0]
6153 1.6.7rc01-02 16 10607 16.so.16.7[.0]
6154 1.6.7 16 10607 16.so.16.7[.0]
6155 1.6.8beta01-02 16 10608 16.so.16.8[.0]
6156 1.6.8rc01-02 16 10608 16.so.16.8[.0]
6157 1.6.8 16 10608 16.so.16.8[.0]
6158 1.6.9beta01-04 16 10609 16.so.16.9[.0]
6159 1.6.9rc01-02 16 10609 16.so.16.9[.0]
6160 1.6.9 16 10609 16.so.16.9[.0]
6161 1.6.10beta01-03 16 10610 16.so.16.10[.0]
6162 1.6.10rc01-04 16 10610 16.so.16.10[.0]
6163 1.6.10 16 10610 16.so.16.10[.0]
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6164
6165Henceforth the source version will match the shared-library minor
6166and patch numbers; the shared-library major version number will be
6167used for changes in backward compatibility, as it is intended. The
6168PNG_PNGLIB_VER macro, which is not used within libpng but is available
6169for applications, is an unsigned integer of the form xyyzz corresponding
6170to the source version x.y.z (leading zeros in y and z). Beta versions
6171were given the previous public release number plus a letter, until
6172version 1.0.6j; from then on they were given the upcoming public
6173release number plus "betaNN" or "rcN".
6174
6175.SH "SEE ALSO"
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6176.BR "png"(5), " libpngpf"(3), " zlib"(3), " deflate"(5), " " and " zlib"(5)
6177
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6178.LP
6179.IR libpng :
6180.IP
6181http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
6182http://www.libpng.org/pub/png
6183
6184.LP
6185.IR zlib :
6186.IP
6187(generally) at the same location as
6188.I libpng
6189or at
6190.br
6191ftp://ftp.info-zip.org/pub/infozip/zlib
6192
6193.LP
6194.IR PNG specification: RFC 2083
6195.IP
6196(generally) at the same location as
6197.I libpng
6198or at
6199.br
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6200ftp://ds.internic.net/rfc/rfc2083.txt
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6201.br
6202or (as a W3C Recommendation) at
6203.br
6204http://www.w3.org/TR/REC-png.html
6205
6206.LP
6207In the case of any inconsistency between the PNG specification
6208and this library, the specification takes precedence.
6209
6210.SH AUTHORS
6211This man page: Glenn Randers-Pehrson
6212<glennrp at users.sourceforge.net>
6213
6214The contributing authors would like to thank all those who helped
6215with testing, bug fixes, and patience. This wouldn't have been
6216possible without all of you.
6217
6218Thanks to Frank J. T. Wojcik for helping with the documentation.
6219
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]6220Libpng version 1.6.10 - March 6, 2014:
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6221Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
6222Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
6223
6224Supported by the PNG development group
6225.br
6226png-mng-implement at lists.sf.net
6227(subscription required; visit
6228png-mng-implement at lists.sourceforge.net (subscription required; visit
6229https://lists.sourceforge.net/lists/listinfo/png-mng-implement
6230to subscribe).
6231
6232.SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
6233
6234(This copy of the libpng notices is provided for your convenience. In case of
6235any discrepancy between this copy and the notices in the file png.h that is
6236included in the libpng distribution, the latter shall prevail.)
6237
6238If you modify libpng you may insert additional notices immediately following
6239this sentence.
6240
Patrick Scotta0bb96c2009-07-22 11:50:02 -0400[diff] [blame]6241This code is released under the libpng license.
6242
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]6243libpng versions 1.2.6, August 15, 2004, through 1.6.10, March 6, 2014, are
Chris Craikb50c2172013-07-29 15:28:30 -0700[diff] [blame]6244Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6245distributed according to the same disclaimer and license as libpng-1.2.5
6246with the following individual added to the list of Contributing Authors
6247
6248 Cosmin Truta
6249
6250libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
6251Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
6252distributed according to the same disclaimer and license as libpng-1.0.6
6253with the following individuals added to the list of Contributing Authors
6254
6255 Simon-Pierre Cadieux
6256 Eric S. Raymond
6257 Gilles Vollant
6258
6259and with the following additions to the disclaimer:
6260
6261 There is no warranty against interference with your
6262 enjoyment of the library or against infringement.
6263 There is no warranty that our efforts or the library
6264 will fulfill any of your particular purposes or needs.
6265 This library is provided with all faults, and the entire
6266 risk of satisfactory quality, performance, accuracy, and
6267 effort is with the user.
6268
6269libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
6270Copyright (c) 1998, 1999 Glenn Randers-Pehrson
6271Distributed according to the same disclaimer and license as libpng-0.96,
6272with the following individuals added to the list of Contributing Authors:
6273
6274 Tom Lane
6275 Glenn Randers-Pehrson
6276 Willem van Schaik
6277
6278libpng versions 0.89, June 1996, through 0.96, May 1997, are
6279Copyright (c) 1996, 1997 Andreas Dilger
6280Distributed according to the same disclaimer and license as libpng-0.88,
6281with the following individuals added to the list of Contributing Authors:
6282
6283 John Bowler
6284 Kevin Bracey
6285 Sam Bushell
6286 Magnus Holmgren
6287 Greg Roelofs
6288 Tom Tanner
6289
6290libpng versions 0.5, May 1995, through 0.88, January 1996, are
6291Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
6292
6293For the purposes of this copyright and license, "Contributing Authors"
6294is defined as the following set of individuals:
6295
6296 Andreas Dilger
6297 Dave Martindale
6298 Guy Eric Schalnat
6299 Paul Schmidt
6300 Tim Wegner
6301
6302The PNG Reference Library is supplied "AS IS". The Contributing Authors
6303and Group 42, Inc. disclaim all warranties, expressed or implied,
6304including, without limitation, the warranties of merchantability and of
6305fitness for any purpose. The Contributing Authors and Group 42, Inc.
6306assume no liability for direct, indirect, incidental, special, exemplary,
6307or consequential damages, which may result from the use of the PNG
6308Reference Library, even if advised of the possibility of such damage.
6309
6310Permission is hereby granted to use, copy, modify, and distribute this
6311source code, or portions hereof, for any purpose, without fee, subject
6312to the following restrictions:
6313
63141. The origin of this source code must not be misrepresented.
6315
63162. Altered versions must be plainly marked as such and
6317 must not be misrepresented as being the original source.
6318
63193. This Copyright notice may not be removed or altered from
6320 any source or altered source distribution.
6321
6322The Contributing Authors and Group 42, Inc. specifically permit, without
6323fee, and encourage the use of this source code as a component to
6324supporting the PNG file format in commercial products. If you use this
6325source code in a product, acknowledgment is not required but would be
6326appreciated.
6327
6328
6329A "png_get_copyright" function is available, for convenient use in "about"
6330boxes and the like:
6331
6332 printf("%s",png_get_copyright(NULL));
6333
6334Also, the PNG logo (in PNG format, of course) is supplied in the
6335files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
6336
6337Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
6338certification mark of the Open Source Initiative.
6339
6340Glenn Randers-Pehrson
6341glennrp at users.sourceforge.net
Sireesh Tripurarib478e662014-05-09 15:15:10 +0530[diff] [blame]6342March 6, 2014
The Android Open Source Project893912b2009-03-03 19:30:05 -0800[diff] [blame]6343
6344.\" end of man page
6345