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annotate libs/libjpeg/README @ 22:d7fe157c402d

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author John Tsiombikas <nuclear@member.fsf.org>
date Sat, 13 Jun 2015 05:32:07 +0300
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nuclear@14 1 The Independent JPEG Group's JPEG software
nuclear@14 2 ==========================================
nuclear@14 3
nuclear@14 4 README for release 8c of 16-Jan-2011
nuclear@14 5 ====================================
nuclear@14 6
nuclear@14 7 This distribution contains the eighth public release of the Independent JPEG
nuclear@14 8 Group's free JPEG software. You are welcome to redistribute this software and
nuclear@14 9 to use it for any purpose, subject to the conditions under LEGAL ISSUES, below.
nuclear@14 10
nuclear@14 11 This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone,
nuclear@14 12 Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson,
nuclear@14 13 Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers,
nuclear@14 14 and other members of the Independent JPEG Group.
nuclear@14 15
nuclear@14 16 IJG is not affiliated with the official ISO JPEG standards committee.
nuclear@14 17
nuclear@14 18
nuclear@14 19 DOCUMENTATION ROADMAP
nuclear@14 20 =====================
nuclear@14 21
nuclear@14 22 This file contains the following sections:
nuclear@14 23
nuclear@14 24 OVERVIEW General description of JPEG and the IJG software.
nuclear@14 25 LEGAL ISSUES Copyright, lack of warranty, terms of distribution.
nuclear@14 26 REFERENCES Where to learn more about JPEG.
nuclear@14 27 ARCHIVE LOCATIONS Where to find newer versions of this software.
nuclear@14 28 ACKNOWLEDGMENTS Special thanks.
nuclear@14 29 FILE FORMAT WARS Software *not* to get.
nuclear@14 30 TO DO Plans for future IJG releases.
nuclear@14 31
nuclear@14 32 Other documentation files in the distribution are:
nuclear@14 33
nuclear@14 34 User documentation:
nuclear@14 35 install.txt How to configure and install the IJG software.
nuclear@14 36 usage.txt Usage instructions for cjpeg, djpeg, jpegtran,
nuclear@14 37 rdjpgcom, and wrjpgcom.
nuclear@14 38 *.1 Unix-style man pages for programs (same info as usage.txt).
nuclear@14 39 wizard.txt Advanced usage instructions for JPEG wizards only.
nuclear@14 40 change.log Version-to-version change highlights.
nuclear@14 41 Programmer and internal documentation:
nuclear@14 42 libjpeg.txt How to use the JPEG library in your own programs.
nuclear@14 43 example.c Sample code for calling the JPEG library.
nuclear@14 44 structure.txt Overview of the JPEG library's internal structure.
nuclear@14 45 filelist.txt Road map of IJG files.
nuclear@14 46 coderules.txt Coding style rules --- please read if you contribute code.
nuclear@14 47
nuclear@14 48 Please read at least the files install.txt and usage.txt. Some information
nuclear@14 49 can also be found in the JPEG FAQ (Frequently Asked Questions) article. See
nuclear@14 50 ARCHIVE LOCATIONS below to find out where to obtain the FAQ article.
nuclear@14 51
nuclear@14 52 If you want to understand how the JPEG code works, we suggest reading one or
nuclear@14 53 more of the REFERENCES, then looking at the documentation files (in roughly
nuclear@14 54 the order listed) before diving into the code.
nuclear@14 55
nuclear@14 56
nuclear@14 57 OVERVIEW
nuclear@14 58 ========
nuclear@14 59
nuclear@14 60 This package contains C software to implement JPEG image encoding, decoding,
nuclear@14 61 and transcoding. JPEG (pronounced "jay-peg") is a standardized compression
nuclear@14 62 method for full-color and gray-scale images.
nuclear@14 63
nuclear@14 64 This software implements JPEG baseline, extended-sequential, and progressive
nuclear@14 65 compression processes. Provision is made for supporting all variants of these
nuclear@14 66 processes, although some uncommon parameter settings aren't implemented yet.
nuclear@14 67 We have made no provision for supporting the hierarchical or lossless
nuclear@14 68 processes defined in the standard.
nuclear@14 69
nuclear@14 70 We provide a set of library routines for reading and writing JPEG image files,
nuclear@14 71 plus two sample applications "cjpeg" and "djpeg", which use the library to
nuclear@14 72 perform conversion between JPEG and some other popular image file formats.
nuclear@14 73 The library is intended to be reused in other applications.
nuclear@14 74
nuclear@14 75 In order to support file conversion and viewing software, we have included
nuclear@14 76 considerable functionality beyond the bare JPEG coding/decoding capability;
nuclear@14 77 for example, the color quantization modules are not strictly part of JPEG
nuclear@14 78 decoding, but they are essential for output to colormapped file formats or
nuclear@14 79 colormapped displays. These extra functions can be compiled out of the
nuclear@14 80 library if not required for a particular application.
nuclear@14 81
nuclear@14 82 We have also included "jpegtran", a utility for lossless transcoding between
nuclear@14 83 different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple
nuclear@14 84 applications for inserting and extracting textual comments in JFIF files.
nuclear@14 85
nuclear@14 86 The emphasis in designing this software has been on achieving portability and
nuclear@14 87 flexibility, while also making it fast enough to be useful. In particular,
nuclear@14 88 the software is not intended to be read as a tutorial on JPEG. (See the
nuclear@14 89 REFERENCES section for introductory material.) Rather, it is intended to
nuclear@14 90 be reliable, portable, industrial-strength code. We do not claim to have
nuclear@14 91 achieved that goal in every aspect of the software, but we strive for it.
nuclear@14 92
nuclear@14 93 We welcome the use of this software as a component of commercial products.
nuclear@14 94 No royalty is required, but we do ask for an acknowledgement in product
nuclear@14 95 documentation, as described under LEGAL ISSUES.
nuclear@14 96
nuclear@14 97
nuclear@14 98 LEGAL ISSUES
nuclear@14 99 ============
nuclear@14 100
nuclear@14 101 In plain English:
nuclear@14 102
nuclear@14 103 1. We don't promise that this software works. (But if you find any bugs,
nuclear@14 104 please let us know!)
nuclear@14 105 2. You can use this software for whatever you want. You don't have to pay us.
nuclear@14 106 3. You may not pretend that you wrote this software. If you use it in a
nuclear@14 107 program, you must acknowledge somewhere in your documentation that
nuclear@14 108 you've used the IJG code.
nuclear@14 109
nuclear@14 110 In legalese:
nuclear@14 111
nuclear@14 112 The authors make NO WARRANTY or representation, either express or implied,
nuclear@14 113 with respect to this software, its quality, accuracy, merchantability, or
nuclear@14 114 fitness for a particular purpose. This software is provided "AS IS", and you,
nuclear@14 115 its user, assume the entire risk as to its quality and accuracy.
nuclear@14 116
nuclear@14 117 This software is copyright (C) 1991-2011, Thomas G. Lane, Guido Vollbeding.
nuclear@14 118 All Rights Reserved except as specified below.
nuclear@14 119
nuclear@14 120 Permission is hereby granted to use, copy, modify, and distribute this
nuclear@14 121 software (or portions thereof) for any purpose, without fee, subject to these
nuclear@14 122 conditions:
nuclear@14 123 (1) If any part of the source code for this software is distributed, then this
nuclear@14 124 README file must be included, with this copyright and no-warranty notice
nuclear@14 125 unaltered; and any additions, deletions, or changes to the original files
nuclear@14 126 must be clearly indicated in accompanying documentation.
nuclear@14 127 (2) If only executable code is distributed, then the accompanying
nuclear@14 128 documentation must state that "this software is based in part on the work of
nuclear@14 129 the Independent JPEG Group".
nuclear@14 130 (3) Permission for use of this software is granted only if the user accepts
nuclear@14 131 full responsibility for any undesirable consequences; the authors accept
nuclear@14 132 NO LIABILITY for damages of any kind.
nuclear@14 133
nuclear@14 134 These conditions apply to any software derived from or based on the IJG code,
nuclear@14 135 not just to the unmodified library. If you use our work, you ought to
nuclear@14 136 acknowledge us.
nuclear@14 137
nuclear@14 138 Permission is NOT granted for the use of any IJG author's name or company name
nuclear@14 139 in advertising or publicity relating to this software or products derived from
nuclear@14 140 it. This software may be referred to only as "the Independent JPEG Group's
nuclear@14 141 software".
nuclear@14 142
nuclear@14 143 We specifically permit and encourage the use of this software as the basis of
nuclear@14 144 commercial products, provided that all warranty or liability claims are
nuclear@14 145 assumed by the product vendor.
nuclear@14 146
nuclear@14 147
nuclear@14 148 ansi2knr.c is included in this distribution by permission of L. Peter Deutsch,
nuclear@14 149 sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA.
nuclear@14 150 ansi2knr.c is NOT covered by the above copyright and conditions, but instead
nuclear@14 151 by the usual distribution terms of the Free Software Foundation; principally,
nuclear@14 152 that you must include source code if you redistribute it. (See the file
nuclear@14 153 ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part
nuclear@14 154 of any program generated from the IJG code, this does not limit you more than
nuclear@14 155 the foregoing paragraphs do.
nuclear@14 156
nuclear@14 157 The Unix configuration script "configure" was produced with GNU Autoconf.
nuclear@14 158 It is copyright by the Free Software Foundation but is freely distributable.
nuclear@14 159 The same holds for its supporting scripts (config.guess, config.sub,
nuclear@14 160 ltmain.sh). Another support script, install-sh, is copyright by X Consortium
nuclear@14 161 but is also freely distributable.
nuclear@14 162
nuclear@14 163 The IJG distribution formerly included code to read and write GIF files.
nuclear@14 164 To avoid entanglement with the Unisys LZW patent, GIF reading support has
nuclear@14 165 been removed altogether, and the GIF writer has been simplified to produce
nuclear@14 166 "uncompressed GIFs". This technique does not use the LZW algorithm; the
nuclear@14 167 resulting GIF files are larger than usual, but are readable by all standard
nuclear@14 168 GIF decoders.
nuclear@14 169
nuclear@14 170 We are required to state that
nuclear@14 171 "The Graphics Interchange Format(c) is the Copyright property of
nuclear@14 172 CompuServe Incorporated. GIF(sm) is a Service Mark property of
nuclear@14 173 CompuServe Incorporated."
nuclear@14 174
nuclear@14 175
nuclear@14 176 REFERENCES
nuclear@14 177 ==========
nuclear@14 178
nuclear@14 179 We recommend reading one or more of these references before trying to
nuclear@14 180 understand the innards of the JPEG software.
nuclear@14 181
nuclear@14 182 The best short technical introduction to the JPEG compression algorithm is
nuclear@14 183 Wallace, Gregory K. "The JPEG Still Picture Compression Standard",
nuclear@14 184 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44.
nuclear@14 185 (Adjacent articles in that issue discuss MPEG motion picture compression,
nuclear@14 186 applications of JPEG, and related topics.) If you don't have the CACM issue
nuclear@14 187 handy, a PostScript file containing a revised version of Wallace's article is
nuclear@14 188 available at http://www.ijg.org/files/wallace.ps.gz. The file (actually
nuclear@14 189 a preprint for an article that appeared in IEEE Trans. Consumer Electronics)
nuclear@14 190 omits the sample images that appeared in CACM, but it includes corrections
nuclear@14 191 and some added material. Note: the Wallace article is copyright ACM and IEEE,
nuclear@14 192 and it may not be used for commercial purposes.
nuclear@14 193
nuclear@14 194 A somewhat less technical, more leisurely introduction to JPEG can be found in
nuclear@14 195 "The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by
nuclear@14 196 M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides
nuclear@14 197 good explanations and example C code for a multitude of compression methods
nuclear@14 198 including JPEG. It is an excellent source if you are comfortable reading C
nuclear@14 199 code but don't know much about data compression in general. The book's JPEG
nuclear@14 200 sample code is far from industrial-strength, but when you are ready to look
nuclear@14 201 at a full implementation, you've got one here...
nuclear@14 202
nuclear@14 203 The best currently available description of JPEG is the textbook "JPEG Still
nuclear@14 204 Image Data Compression Standard" by William B. Pennebaker and Joan L.
nuclear@14 205 Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1.
nuclear@14 206 Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG
nuclear@14 207 standards (DIS 10918-1 and draft DIS 10918-2).
nuclear@14 208 Although this is by far the most detailed and comprehensive exposition of
nuclear@14 209 JPEG publicly available, we point out that it is still missing an explanation
nuclear@14 210 of the most essential properties and algorithms of the underlying DCT
nuclear@14 211 technology.
nuclear@14 212 If you think that you know about DCT-based JPEG after reading this book,
nuclear@14 213 then you are in delusion. The real fundamentals and corresponding potential
nuclear@14 214 of DCT-based JPEG are not publicly known so far, and that is the reason for
nuclear@14 215 all the mistaken developments taking place in the image coding domain.
nuclear@14 216
nuclear@14 217 The original JPEG standard is divided into two parts, Part 1 being the actual
nuclear@14 218 specification, while Part 2 covers compliance testing methods. Part 1 is
nuclear@14 219 titled "Digital Compression and Coding of Continuous-tone Still Images,
nuclear@14 220 Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS
nuclear@14 221 10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of
nuclear@14 222 Continuous-tone Still Images, Part 2: Compliance testing" and has document
nuclear@14 223 numbers ISO/IEC IS 10918-2, ITU-T T.83.
nuclear@14 224 IJG JPEG 8 introduces an implementation of the JPEG SmartScale extension
nuclear@14 225 which is specified in a contributed document at ITU and ISO with title "ITU-T
nuclear@14 226 JPEG-Plus Proposal for Extending ITU-T T.81 for Advanced Image Coding", April
nuclear@14 227 2006, Geneva, Switzerland. The latest version of the document is Revision 3.
nuclear@14 228
nuclear@14 229 The JPEG standard does not specify all details of an interchangeable file
nuclear@14 230 format. For the omitted details we follow the "JFIF" conventions, revision
nuclear@14 231 1.02. JFIF 1.02 has been adopted as an Ecma International Technical Report
nuclear@14 232 and thus received a formal publication status. It is available as a free
nuclear@14 233 download in PDF format from
nuclear@14 234 http://www.ecma-international.org/publications/techreports/E-TR-098.htm.
nuclear@14 235 A PostScript version of the JFIF document is available at
nuclear@14 236 http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at
nuclear@14 237 http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures.
nuclear@14 238
nuclear@14 239 The TIFF 6.0 file format specification can be obtained by FTP from
nuclear@14 240 ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme
nuclear@14 241 found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems.
nuclear@14 242 IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6).
nuclear@14 243 Instead, we recommend the JPEG design proposed by TIFF Technical Note #2
nuclear@14 244 (Compression tag 7). Copies of this Note can be obtained from
nuclear@14 245 http://www.ijg.org/files/. It is expected that the next revision
nuclear@14 246 of the TIFF spec will replace the 6.0 JPEG design with the Note's design.
nuclear@14 247 Although IJG's own code does not support TIFF/JPEG, the free libtiff library
nuclear@14 248 uses our library to implement TIFF/JPEG per the Note.
nuclear@14 249
nuclear@14 250
nuclear@14 251 ARCHIVE LOCATIONS
nuclear@14 252 =================
nuclear@14 253
nuclear@14 254 The "official" archive site for this software is www.ijg.org.
nuclear@14 255 The most recent released version can always be found there in
nuclear@14 256 directory "files". This particular version will be archived as
nuclear@14 257 http://www.ijg.org/files/jpegsrc.v8c.tar.gz, and in Windows-compatible
nuclear@14 258 "zip" archive format as http://www.ijg.org/files/jpegsr8c.zip.
nuclear@14 259
nuclear@14 260 The JPEG FAQ (Frequently Asked Questions) article is a source of some
nuclear@14 261 general information about JPEG.
nuclear@14 262 It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/
nuclear@14 263 and other news.answers archive sites, including the official news.answers
nuclear@14 264 archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/.
nuclear@14 265 If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu
nuclear@14 266 with body
nuclear@14 267 send usenet/news.answers/jpeg-faq/part1
nuclear@14 268 send usenet/news.answers/jpeg-faq/part2
nuclear@14 269
nuclear@14 270
nuclear@14 271 ACKNOWLEDGMENTS
nuclear@14 272 ===============
nuclear@14 273
nuclear@14 274 Thank to Juergen Bruder for providing me with a copy of the common DCT
nuclear@14 275 algorithm article, only to find out that I had come to the same result
nuclear@14 276 in a more direct and comprehensible way with a more generative approach.
nuclear@14 277
nuclear@14 278 Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the
nuclear@14 279 ITU JPEG (Study Group 16) meeting in Geneva, Switzerland.
nuclear@14 280
nuclear@14 281 Thank to Thomas Wiegand and Gary Sullivan for inviting me to the
nuclear@14 282 Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland.
nuclear@14 283
nuclear@14 284 Thank to John Korejwa and Massimo Ballerini for inviting me to
nuclear@14 285 fruitful consultations in Boston, MA and Milan, Italy.
nuclear@14 286
nuclear@14 287 Thank to Hendrik Elstner, Roland Fassauer, Simone Zuck, Guenther
nuclear@14 288 Maier-Gerber, Walter Stoeber, Fred Schmitz, and Norbert Braunagel
nuclear@14 289 for corresponding business development.
nuclear@14 290
nuclear@14 291 Thank to Nico Zschach and Dirk Stelling of the technical support team
nuclear@14 292 at the Digital Images company in Halle for providing me with extra
nuclear@14 293 equipment for configuration tests.
nuclear@14 294
nuclear@14 295 Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful
nuclear@14 296 communication about JPEG configuration in Sigma Photo Pro software.
nuclear@14 297
nuclear@14 298 Thank to Andrew Finkenstadt for hosting the ijg.org site.
nuclear@14 299
nuclear@14 300 Last but not least special thank to Thomas G. Lane for the original
nuclear@14 301 design and development of this singular software package.
nuclear@14 302
nuclear@14 303
nuclear@14 304 FILE FORMAT WARS
nuclear@14 305 ================
nuclear@14 306
nuclear@14 307 The ISO JPEG standards committee actually promotes different formats like
nuclear@14 308 "JPEG 2000" or "JPEG XR" which are incompatible with original DCT-based
nuclear@14 309 JPEG and which are based on faulty technologies. IJG therefore does not
nuclear@14 310 and will not support such momentary mistakes (see REFERENCES).
nuclear@14 311 We have little or no sympathy for the promotion of these formats. Indeed,
nuclear@14 312 one of the original reasons for developing this free software was to help
nuclear@14 313 force convergence on common, interoperable format standards for JPEG files.
nuclear@14 314 Don't use an incompatible file format!
nuclear@14 315 (In any case, our decoder will remain capable of reading existing JPEG
nuclear@14 316 image files indefinitely.)
nuclear@14 317
nuclear@14 318
nuclear@14 319 TO DO
nuclear@14 320 =====
nuclear@14 321
nuclear@14 322 Version 8 is the first release of a new generation JPEG standard
nuclear@14 323 to overcome the limitations of the original JPEG specification.
nuclear@14 324 More features are being prepared for coming releases...
nuclear@14 325
nuclear@14 326 Please send bug reports, offers of help, etc. to jpeg-info@uc.ag.