The Independent JPEG Group's JPEG software v4
diff --git a/jdsample.c b/jdsample.c
index 71fb453..3f49e29 100644
--- a/jdsample.c
+++ b/jdsample.c
@@ -5,37 +5,48 @@
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
- * This file contains un-subsampling routines.
- * These routines are invoked via the unsubsample and
- * unsubsample_init/term methods.
+ * This file contains upsampling routines.
+ * These routines are invoked via the upsample and
+ * upsample_init/term methods.
+ *
+ * An excellent reference for image resampling is
+ * Digital Image Warping, George Wolberg, 1990.
+ * Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
*/
#include "jinclude.h"
/*
- * Initialize for un-subsampling a scan.
+ * Initialize for upsampling a scan.
*/
METHODDEF void
-unsubsample_init (decompress_info_ptr cinfo)
+upsample_init (decompress_info_ptr cinfo)
{
/* no work for now */
}
/*
- * Un-subsample pixel values of a single component.
+ * Upsample pixel values of a single component.
* This version handles any integral sampling ratios.
+ *
* This is not used for typical JPEG files, so it need not be fast.
+ * Nor, for that matter, is it particularly accurate: the algorithm is
+ * simple replication of the input pixel onto the corresponding output
+ * pixels. The hi-falutin sampling literature refers to this as a
+ * "box filter". A box filter tends to introduce visible artifacts,
+ * so if you are actually going to use 3:1 or 4:1 sampling ratios
+ * you would be well advised to improve this code.
*/
METHODDEF void
-int_unsubsample (decompress_info_ptr cinfo, int which_component,
- long input_cols, int input_rows,
- long output_cols, int output_rows,
- JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
- JSAMPARRAY output_data)
+int_upsample (decompress_info_ptr cinfo, int which_component,
+ long input_cols, int input_rows,
+ long output_cols, int output_rows,
+ JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
+ JSAMPARRAY output_data)
{
jpeg_component_info * compptr = cinfo->cur_comp_info[which_component];
register JSAMPROW inptr, outptr;
@@ -51,7 +62,7 @@
(input_cols % compptr->h_samp_factor) != 0 ||
(output_cols % cinfo->max_h_samp_factor) != 0 ||
output_cols*compptr->h_samp_factor != input_cols*cinfo->max_h_samp_factor)
- ERREXIT(cinfo->emethods, "Bogus unsubsample parameters");
+ ERREXIT(cinfo->emethods, "Bogus upsample parameters");
#endif
h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor;
@@ -74,95 +85,149 @@
/*
- * Un-subsample pixel values of a single component.
- * This version handles the extremely common case of
- * horizontal expansion by 2 and any integral vertical expansion.
+ * Upsample pixel values of a single component.
+ * This version handles the common case of 2:1 horizontal and 1:1 vertical.
+ *
+ * The upsampling algorithm is linear interpolation between pixel centers,
+ * also known as a "triangle filter". This is a good compromise between
+ * speed and visual quality. The centers of the output pixels are 1/4 and 3/4
+ * of the way between input pixel centers.
*/
METHODDEF void
-h2_unsubsample (decompress_info_ptr cinfo, int which_component,
- long input_cols, int input_rows,
- long output_cols, int output_rows,
- JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
- JSAMPARRAY output_data)
+h2v1_upsample (decompress_info_ptr cinfo, int which_component,
+ long input_cols, int input_rows,
+ long output_cols, int output_rows,
+ JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
+ JSAMPARRAY output_data)
{
- jpeg_component_info * compptr = cinfo->cur_comp_info[which_component];
register JSAMPROW inptr, outptr;
- register JSAMPLE invalue;
- short v_expand, v;
- int inrow, outrow;
- register long incol;
+ register int invalue;
+ int inrow;
+ register long colctr;
#ifdef DEBUG /* for debugging pipeline controller */
+ jpeg_component_info * compptr = cinfo->cur_comp_info[which_component];
if (input_rows != compptr->v_samp_factor ||
output_rows != cinfo->max_v_samp_factor ||
(input_cols % compptr->h_samp_factor) != 0 ||
(output_cols % cinfo->max_h_samp_factor) != 0 ||
output_cols*compptr->h_samp_factor != input_cols*cinfo->max_h_samp_factor)
- ERREXIT(cinfo->emethods, "Bogus unsubsample parameters");
+ ERREXIT(cinfo->emethods, "Bogus upsample parameters");
#endif
- v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor;
+ for (inrow = 0; inrow < input_rows; inrow++) {
+ inptr = input_data[inrow];
+ outptr = output_data[inrow];
+ /* Special case for first column */
+ invalue = GETJSAMPLE(*inptr++);
+ *outptr++ = (JSAMPLE) invalue;
+ *outptr++ = (JSAMPLE) ((invalue * 3 + GETJSAMPLE(*inptr) + 2) >> 2);
-/* The subsampled image width will always be a multiple of DCTSIZE,
- * so we can unroll the inner loop.
+ for (colctr = input_cols - 2; colctr > 0; colctr--) {
+ /* General case: 3/4 * nearer pixel + 1/4 * further pixel */
+ invalue = GETJSAMPLE(*inptr++) * 3;
+ *outptr++ = (JSAMPLE) ((invalue + GETJSAMPLE(inptr[-2]) + 2) >> 2);
+ *outptr++ = (JSAMPLE) ((invalue + GETJSAMPLE(*inptr) + 2) >> 2);
+ }
+
+ /* Special case for last column */
+ invalue = GETJSAMPLE(*inptr);
+ *outptr++ = (JSAMPLE) ((invalue * 3 + GETJSAMPLE(inptr[-1]) + 2) >> 2);
+ *outptr++ = (JSAMPLE) invalue;
+ }
+}
+
+
+/*
+ * Upsample pixel values of a single component.
+ * This version handles the common case of 2:1 horizontal and 2:1 vertical.
+ *
+ * The upsampling algorithm is linear interpolation between pixel centers,
+ * also known as a "triangle filter". This is a good compromise between
+ * speed and visual quality. The centers of the output pixels are 1/4 and 3/4
+ * of the way between input pixel centers.
*/
+METHODDEF void
+h2v2_upsample (decompress_info_ptr cinfo, int which_component,
+ long input_cols, int input_rows,
+ long output_cols, int output_rows,
+ JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
+ JSAMPARRAY output_data)
+{
+ register JSAMPROW inptr0, inptr1, outptr;
+#ifdef EIGHT_BIT_SAMPLES
+ register int thiscolsum, lastcolsum, nextcolsum;
+#else
+ register INT32 thiscolsum, lastcolsum, nextcolsum;
+#endif
+ int inrow, outrow, v;
+ register long colctr;
+
+#ifdef DEBUG /* for debugging pipeline controller */
+ jpeg_component_info * compptr = cinfo->cur_comp_info[which_component];
+ if (input_rows != compptr->v_samp_factor ||
+ output_rows != cinfo->max_v_samp_factor ||
+ (input_cols % compptr->h_samp_factor) != 0 ||
+ (output_cols % cinfo->max_h_samp_factor) != 0 ||
+ output_cols*compptr->h_samp_factor != input_cols*cinfo->max_h_samp_factor)
+ ERREXIT(cinfo->emethods, "Bogus upsample parameters");
+#endif
+
outrow = 0;
for (inrow = 0; inrow < input_rows; inrow++) {
- for (v = 0; v < v_expand; v++) {
- inptr = input_data[inrow];
+ for (v = 0; v < 2; v++) {
+ /* inptr0 points to nearest input row, inptr1 points to next nearest */
+ inptr0 = input_data[inrow];
+ if (v == 0) { /* next nearest is row above */
+ if (inrow == 0)
+ inptr1 = above[input_rows-1];
+ else
+ inptr1 = input_data[inrow-1];
+ } else { /* next nearest is row below */
+ if (inrow == input_rows-1)
+ inptr1 = below[0];
+ else
+ inptr1 = input_data[inrow+1];
+ }
outptr = output_data[outrow++];
-#if DCTSIZE == 8
- for (incol = 0; incol < input_cols; incol += DCTSIZE) {
- invalue = GETJSAMPLE(*inptr++);
- *outptr++ = invalue;
- *outptr++ = invalue;
- invalue = GETJSAMPLE(*inptr++);
- *outptr++ = invalue;
- *outptr++ = invalue;
- invalue = GETJSAMPLE(*inptr++);
- *outptr++ = invalue;
- *outptr++ = invalue;
- invalue = GETJSAMPLE(*inptr++);
- *outptr++ = invalue;
- *outptr++ = invalue;
- invalue = GETJSAMPLE(*inptr++);
- *outptr++ = invalue;
- *outptr++ = invalue;
- invalue = GETJSAMPLE(*inptr++);
- *outptr++ = invalue;
- *outptr++ = invalue;
- invalue = GETJSAMPLE(*inptr++);
- *outptr++ = invalue;
- *outptr++ = invalue;
- invalue = GETJSAMPLE(*inptr++);
- *outptr++ = invalue;
- *outptr++ = invalue;
+
+ /* Special case for first column */
+ thiscolsum = GETJSAMPLE(*inptr0++) * 3 + GETJSAMPLE(*inptr1++);
+ nextcolsum = GETJSAMPLE(*inptr0++) * 3 + GETJSAMPLE(*inptr1++);
+ *outptr++ = (JSAMPLE) ((thiscolsum * 4 + 8) >> 4);
+ *outptr++ = (JSAMPLE) ((thiscolsum * 3 + nextcolsum + 8) >> 4);
+ lastcolsum = thiscolsum; thiscolsum = nextcolsum;
+
+ for (colctr = input_cols - 2; colctr > 0; colctr--) {
+ /* General case: 3/4 * nearer pixel + 1/4 * further pixel in each */
+ /* dimension, thus 9/16, 3/16, 3/16, 1/16 overall */
+ nextcolsum = GETJSAMPLE(*inptr0++) * 3 + GETJSAMPLE(*inptr1++);
+ *outptr++ = (JSAMPLE) ((thiscolsum * 3 + lastcolsum + 8) >> 4);
+ *outptr++ = (JSAMPLE) ((thiscolsum * 3 + nextcolsum + 8) >> 4);
+ lastcolsum = thiscolsum; thiscolsum = nextcolsum;
}
-#else /* nonstandard DCTSIZE */
- for (incol = 0; incol < input_cols; incol++) {
- invalue = GETJSAMPLE(*inptr++);
- *outptr++ = invalue;
- *outptr++ = invalue;
- }
-#endif
+
+ /* Special case for last column */
+ *outptr++ = (JSAMPLE) ((thiscolsum * 3 + lastcolsum + 8) >> 4);
+ *outptr++ = (JSAMPLE) ((thiscolsum * 4 + 8) >> 4);
}
}
}
/*
- * Un-subsample pixel values of a single component.
+ * Upsample pixel values of a single component.
* This version handles the special case of a full-size component.
*/
METHODDEF void
-fullsize_unsubsample (decompress_info_ptr cinfo, int which_component,
- long input_cols, int input_rows,
- long output_cols, int output_rows,
- JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
- JSAMPARRAY output_data)
+fullsize_upsample (decompress_info_ptr cinfo, int which_component,
+ long input_cols, int input_rows,
+ long output_cols, int output_rows,
+ JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
+ JSAMPARRAY output_data)
{
#ifdef DEBUG /* for debugging pipeline controller */
if (input_cols != output_cols || input_rows != output_rows)
@@ -179,7 +244,7 @@
*/
METHODDEF void
-unsubsample_term (decompress_info_ptr cinfo)
+upsample_term (decompress_info_ptr cinfo)
{
/* no work for now */
}
@@ -187,34 +252,37 @@
/*
- * The method selection routine for unsubsampling.
+ * The method selection routine for upsampling.
* Note that we must select a routine for each component.
*/
GLOBAL void
-jselunsubsample (decompress_info_ptr cinfo)
+jselupsample (decompress_info_ptr cinfo)
{
short ci;
jpeg_component_info * compptr;
if (cinfo->CCIR601_sampling)
- ERREXIT(cinfo->emethods, "CCIR601 subsampling not implemented yet");
+ ERREXIT(cinfo->emethods, "CCIR601 upsampling not implemented yet");
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
if (compptr->h_samp_factor == cinfo->max_h_samp_factor &&
compptr->v_samp_factor == cinfo->max_v_samp_factor)
- cinfo->methods->unsubsample[ci] = fullsize_unsubsample;
+ cinfo->methods->upsample[ci] = fullsize_upsample;
else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
- (cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0)
- cinfo->methods->unsubsample[ci] = h2_unsubsample;
+ compptr->v_samp_factor == cinfo->max_v_samp_factor)
+ cinfo->methods->upsample[ci] = h2v1_upsample;
+ else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
+ compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor)
+ cinfo->methods->upsample[ci] = h2v2_upsample;
else if ((cinfo->max_h_samp_factor % compptr->h_samp_factor) == 0 &&
(cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0)
- cinfo->methods->unsubsample[ci] = int_unsubsample;
+ cinfo->methods->upsample[ci] = int_upsample;
else
- ERREXIT(cinfo->emethods, "Fractional subsampling not implemented yet");
+ ERREXIT(cinfo->emethods, "Fractional upsampling not implemented yet");
}
- cinfo->methods->unsubsample_init = unsubsample_init;
- cinfo->methods->unsubsample_term = unsubsample_term;
+ cinfo->methods->upsample_init = upsample_init;
+ cinfo->methods->upsample_term = upsample_term;
}