noel@chromium.org | 3395bcc | 2014-04-14 06:56:00 +0000 | [diff] [blame] | 1 | libjpeg-turbo note: This file has been modified by The libjpeg-turbo Project |
| 2 | to include only information relevant to libjpeg-turbo, to wordsmith certain |
| 3 | sections, and to remove impolitic language that existed in the libjpeg v8 |
Tom Hudson | 0d47d2d | 2016-05-04 13:22:56 -0400 | [diff] [blame] | 4 | README. It is included only for reference. Please see README.md for |
noel@chromium.org | 3395bcc | 2014-04-14 06:56:00 +0000 | [diff] [blame] | 5 | information specific to libjpeg-turbo. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 6 | |
| 7 | |
| 8 | The Independent JPEG Group's JPEG software |
| 9 | ========================================== |
| 10 | |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 11 | This distribution contains a release of the Independent JPEG Group's free JPEG |
| 12 | software. You are welcome to redistribute this software and to use it for any |
| 13 | purpose, subject to the conditions under LEGAL ISSUES, below. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 14 | |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 15 | This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone, |
| 16 | Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson, |
| 17 | Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers, |
| 18 | and other members of the Independent JPEG Group. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 19 | |
noel@chromium.org | 3395bcc | 2014-04-14 06:56:00 +0000 | [diff] [blame] | 20 | IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee |
| 21 | (also known as JPEG, together with ITU-T SG16). |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 22 | |
| 23 | |
| 24 | DOCUMENTATION ROADMAP |
| 25 | ===================== |
| 26 | |
| 27 | This file contains the following sections: |
| 28 | |
| 29 | OVERVIEW General description of JPEG and the IJG software. |
| 30 | LEGAL ISSUES Copyright, lack of warranty, terms of distribution. |
| 31 | REFERENCES Where to learn more about JPEG. |
| 32 | ARCHIVE LOCATIONS Where to find newer versions of this software. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 33 | FILE FORMAT WARS Software *not* to get. |
| 34 | TO DO Plans for future IJG releases. |
| 35 | |
| 36 | Other documentation files in the distribution are: |
| 37 | |
| 38 | User documentation: |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 39 | usage.txt Usage instructions for cjpeg, djpeg, jpegtran, |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 40 | rdjpgcom, and wrjpgcom. |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 41 | *.1 Unix-style man pages for programs (same info as usage.txt). |
| 42 | wizard.txt Advanced usage instructions for JPEG wizards only. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 43 | change.log Version-to-version change highlights. |
| 44 | Programmer and internal documentation: |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 45 | libjpeg.txt How to use the JPEG library in your own programs. |
Chris Blume | cca8c4d | 2019-03-01 01:09:50 -0800 | [diff] [blame] | 46 | example.txt Sample code for calling the JPEG library. |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 47 | structure.txt Overview of the JPEG library's internal structure. |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 48 | coderules.txt Coding style rules --- please read if you contribute code. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 49 | |
Tom Hudson | 0d47d2d | 2016-05-04 13:22:56 -0400 | [diff] [blame] | 50 | Please read at least usage.txt. Some information can also be found in the JPEG |
| 51 | FAQ (Frequently Asked Questions) article. See ARCHIVE LOCATIONS below to find |
| 52 | out where to obtain the FAQ article. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 53 | |
| 54 | If you want to understand how the JPEG code works, we suggest reading one or |
| 55 | more of the REFERENCES, then looking at the documentation files (in roughly |
| 56 | the order listed) before diving into the code. |
| 57 | |
| 58 | |
| 59 | OVERVIEW |
| 60 | ======== |
| 61 | |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 62 | This package contains C software to implement JPEG image encoding, decoding, |
| 63 | and transcoding. JPEG (pronounced "jay-peg") is a standardized compression |
Tom Hudson | 0d47d2d | 2016-05-04 13:22:56 -0400 | [diff] [blame] | 64 | method for full-color and grayscale images. JPEG's strong suit is compressing |
hbono@chromium.org | 0ec930e | 2012-01-18 07:01:04 +0000 | [diff] [blame] | 65 | photographic images or other types of images that have smooth color and |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 66 | brightness transitions between neighboring pixels. Images with sharp lines or |
| 67 | other abrupt features may not compress well with JPEG, and a higher JPEG |
| 68 | quality may have to be used to avoid visible compression artifacts with such |
| 69 | images. |
| 70 | |
| 71 | JPEG is lossy, meaning that the output pixels are not necessarily identical to |
| 72 | the input pixels. However, on photographic content and other "smooth" images, |
| 73 | very good compression ratios can be obtained with no visible compression |
| 74 | artifacts, and extremely high compression ratios are possible if you are |
| 75 | willing to sacrifice image quality (by reducing the "quality" setting in the |
| 76 | compressor.) |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 77 | |
| 78 | This software implements JPEG baseline, extended-sequential, and progressive |
| 79 | compression processes. Provision is made for supporting all variants of these |
| 80 | processes, although some uncommon parameter settings aren't implemented yet. |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 81 | We have made no provision for supporting the hierarchical or lossless |
| 82 | processes defined in the standard. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 83 | |
| 84 | We provide a set of library routines for reading and writing JPEG image files, |
| 85 | plus two sample applications "cjpeg" and "djpeg", which use the library to |
| 86 | perform conversion between JPEG and some other popular image file formats. |
| 87 | The library is intended to be reused in other applications. |
| 88 | |
| 89 | In order to support file conversion and viewing software, we have included |
| 90 | considerable functionality beyond the bare JPEG coding/decoding capability; |
| 91 | for example, the color quantization modules are not strictly part of JPEG |
| 92 | decoding, but they are essential for output to colormapped file formats or |
| 93 | colormapped displays. These extra functions can be compiled out of the |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 94 | library if not required for a particular application. |
| 95 | |
| 96 | We have also included "jpegtran", a utility for lossless transcoding between |
| 97 | different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple |
| 98 | applications for inserting and extracting textual comments in JFIF files. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 99 | |
| 100 | The emphasis in designing this software has been on achieving portability and |
| 101 | flexibility, while also making it fast enough to be useful. In particular, |
| 102 | the software is not intended to be read as a tutorial on JPEG. (See the |
| 103 | REFERENCES section for introductory material.) Rather, it is intended to |
| 104 | be reliable, portable, industrial-strength code. We do not claim to have |
| 105 | achieved that goal in every aspect of the software, but we strive for it. |
| 106 | |
| 107 | We welcome the use of this software as a component of commercial products. |
| 108 | No royalty is required, but we do ask for an acknowledgement in product |
| 109 | documentation, as described under LEGAL ISSUES. |
| 110 | |
| 111 | |
| 112 | LEGAL ISSUES |
| 113 | ============ |
| 114 | |
| 115 | In plain English: |
| 116 | |
| 117 | 1. We don't promise that this software works. (But if you find any bugs, |
| 118 | please let us know!) |
| 119 | 2. You can use this software for whatever you want. You don't have to pay us. |
| 120 | 3. You may not pretend that you wrote this software. If you use it in a |
| 121 | program, you must acknowledge somewhere in your documentation that |
| 122 | you've used the IJG code. |
| 123 | |
| 124 | In legalese: |
| 125 | |
| 126 | The authors make NO WARRANTY or representation, either express or implied, |
| 127 | with respect to this software, its quality, accuracy, merchantability, or |
| 128 | fitness for a particular purpose. This software is provided "AS IS", and you, |
| 129 | its user, assume the entire risk as to its quality and accuracy. |
| 130 | |
Jonathan Wright | bbb8282 | 2020-11-25 13:36:43 +0000 | [diff] [blame] | 131 | This software is copyright (C) 1991-2020, Thomas G. Lane, Guido Vollbeding. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 132 | All Rights Reserved except as specified below. |
| 133 | |
| 134 | Permission is hereby granted to use, copy, modify, and distribute this |
| 135 | software (or portions thereof) for any purpose, without fee, subject to these |
| 136 | conditions: |
| 137 | (1) If any part of the source code for this software is distributed, then this |
| 138 | README file must be included, with this copyright and no-warranty notice |
| 139 | unaltered; and any additions, deletions, or changes to the original files |
| 140 | must be clearly indicated in accompanying documentation. |
| 141 | (2) If only executable code is distributed, then the accompanying |
| 142 | documentation must state that "this software is based in part on the work of |
| 143 | the Independent JPEG Group". |
| 144 | (3) Permission for use of this software is granted only if the user accepts |
| 145 | full responsibility for any undesirable consequences; the authors accept |
| 146 | NO LIABILITY for damages of any kind. |
| 147 | |
| 148 | These conditions apply to any software derived from or based on the IJG code, |
| 149 | not just to the unmodified library. If you use our work, you ought to |
| 150 | acknowledge us. |
| 151 | |
| 152 | Permission is NOT granted for the use of any IJG author's name or company name |
| 153 | in advertising or publicity relating to this software or products derived from |
| 154 | it. This software may be referred to only as "the Independent JPEG Group's |
| 155 | software". |
| 156 | |
| 157 | We specifically permit and encourage the use of this software as the basis of |
| 158 | commercial products, provided that all warranty or liability claims are |
| 159 | assumed by the product vendor. |
| 160 | |
| 161 | |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 162 | REFERENCES |
| 163 | ========== |
| 164 | |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 165 | We recommend reading one or more of these references before trying to |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 166 | understand the innards of the JPEG software. |
| 167 | |
| 168 | The best short technical introduction to the JPEG compression algorithm is |
Chris Blume | cca8c4d | 2019-03-01 01:09:50 -0800 | [diff] [blame] | 169 | Wallace, Gregory K. "The JPEG Still Picture Compression Standard", |
| 170 | Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 171 | (Adjacent articles in that issue discuss MPEG motion picture compression, |
| 172 | applications of JPEG, and related topics.) If you don't have the CACM issue |
Tom Hudson | 0d47d2d | 2016-05-04 13:22:56 -0400 | [diff] [blame] | 173 | handy, a PDF file containing a revised version of Wallace's article is |
| 174 | available at http://www.ijg.org/files/Wallace.JPEG.pdf. The file (actually |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 175 | a preprint for an article that appeared in IEEE Trans. Consumer Electronics) |
| 176 | omits the sample images that appeared in CACM, but it includes corrections |
| 177 | and some added material. Note: the Wallace article is copyright ACM and IEEE, |
| 178 | and it may not be used for commercial purposes. |
| 179 | |
| 180 | A somewhat less technical, more leisurely introduction to JPEG can be found in |
| 181 | "The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by |
| 182 | M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides |
| 183 | good explanations and example C code for a multitude of compression methods |
| 184 | including JPEG. It is an excellent source if you are comfortable reading C |
| 185 | code but don't know much about data compression in general. The book's JPEG |
| 186 | sample code is far from industrial-strength, but when you are ready to look |
| 187 | at a full implementation, you've got one here... |
| 188 | |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 189 | The best currently available description of JPEG is the textbook "JPEG Still |
| 190 | Image Data Compression Standard" by William B. Pennebaker and Joan L. |
| 191 | Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. |
| 192 | Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG |
| 193 | standards (DIS 10918-1 and draft DIS 10918-2). |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 194 | |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 195 | The original JPEG standard is divided into two parts, Part 1 being the actual |
| 196 | specification, while Part 2 covers compliance testing methods. Part 1 is |
| 197 | titled "Digital Compression and Coding of Continuous-tone Still Images, |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 198 | Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS |
| 199 | 10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of |
| 200 | Continuous-tone Still Images, Part 2: Compliance testing" and has document |
| 201 | numbers ISO/IEC IS 10918-2, ITU-T T.83. |
| 202 | |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 203 | The JPEG standard does not specify all details of an interchangeable file |
Chris Blume | cca8c4d | 2019-03-01 01:09:50 -0800 | [diff] [blame] | 204 | format. For the omitted details, we follow the "JFIF" conventions, revision |
| 205 | 1.02. JFIF version 1 has been adopted as ISO/IEC 10918-5 (05/2013) and |
| 206 | Recommendation ITU-T T.871 (05/2011): Information technology - Digital |
| 207 | compression and coding of continuous-tone still images: JPEG File Interchange |
| 208 | Format (JFIF). It is available as a free download in PDF file format from |
| 209 | https://www.iso.org/standard/54989.html and http://www.itu.int/rec/T-REC-T.871. |
| 210 | A PDF file of the older JFIF 1.02 specification is available at |
| 211 | http://www.w3.org/Graphics/JPEG/jfif3.pdf. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 212 | |
Jonathan Wright | bbb8282 | 2020-11-25 13:36:43 +0000 | [diff] [blame] | 213 | The TIFF 6.0 file format specification can be obtained from |
| 214 | http://mirrors.ctan.org/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation |
| 215 | scheme found in the TIFF 6.0 spec of 3-June-92 has a number of serious |
| 216 | problems. IJG does not recommend use of the TIFF 6.0 design (TIFF Compression |
| 217 | tag 6). Instead, we recommend the JPEG design proposed by TIFF Technical Note |
| 218 | #2 (Compression tag 7). Copies of this Note can be obtained from |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 219 | http://www.ijg.org/files/. It is expected that the next revision |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 220 | of the TIFF spec will replace the 6.0 JPEG design with the Note's design. |
| 221 | Although IJG's own code does not support TIFF/JPEG, the free libtiff library |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 222 | uses our library to implement TIFF/JPEG per the Note. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 223 | |
| 224 | |
| 225 | ARCHIVE LOCATIONS |
| 226 | ================= |
| 227 | |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 228 | The "official" archive site for this software is www.ijg.org. |
| 229 | The most recent released version can always be found there in |
Tom Hudson | 0d47d2d | 2016-05-04 13:22:56 -0400 | [diff] [blame] | 230 | directory "files". |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 231 | |
hbono@chromium.org | 9862697 | 2011-08-03 03:13:08 +0000 | [diff] [blame] | 232 | The JPEG FAQ (Frequently Asked Questions) article is a source of some |
Jonathan Wright | bbb8282 | 2020-11-25 13:36:43 +0000 | [diff] [blame] | 233 | general information about JPEG. It is available at |
| 234 | http://www.faqs.org/faqs/jpeg-faq. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 235 | |
| 236 | |
Chris Blume | cca8c4d | 2019-03-01 01:09:50 -0800 | [diff] [blame] | 237 | FILE FORMAT COMPATIBILITY |
| 238 | ========================= |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 239 | |
Chris Blume | cca8c4d | 2019-03-01 01:09:50 -0800 | [diff] [blame] | 240 | This software implements ITU T.81 | ISO/IEC 10918 with some extensions from |
| 241 | ITU T.871 | ISO/IEC 10918-5 (JPEG File Interchange Format-- see REFERENCES). |
| 242 | Informally, the term "JPEG image" or "JPEG file" most often refers to JFIF or |
| 243 | a subset thereof, but there are other formats containing the name "JPEG" that |
| 244 | are incompatible with the DCT-based JPEG standard or with JFIF (for instance, |
| 245 | JPEG 2000 and JPEG XR). This software therefore does not support these |
| 246 | formats. Indeed, one of the original reasons for developing this free software |
| 247 | was to help force convergence on a common, interoperable format standard for |
| 248 | JPEG files. |
| 249 | |
| 250 | JFIF is a minimal or "low end" representation. TIFF/JPEG (TIFF revision 6.0 as |
| 251 | modified by TIFF Technical Note #2) can be used for "high end" applications |
| 252 | that need to record a lot of additional data about an image. |
hbono@chromium.org | f0c4f33 | 2010-11-01 05:14:55 +0000 | [diff] [blame] | 253 | |
| 254 | |
| 255 | TO DO |
| 256 | ===== |
| 257 | |
hbono@chromium.org | df5ffdd | 2012-05-11 07:46:03 +0000 | [diff] [blame] | 258 | Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org. |