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1The Independent JPEG Group's JPEG software 2========================================== 3 4README for release 8d of 15-Jan-2012 5==================================== 6 7This distribution contains the eighth public release of the Independent JPEG 8Group's free JPEG software. You are welcome to redistribute this software and 9to use it for any purpose, subject to the conditions under LEGAL ISSUES, below. 10 11This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone, 12Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson, 13Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers, 14and other members of the Independent JPEG Group. 15 16IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee 17(also known as JPEG, together with ITU-T SG16). 18 19 20DOCUMENTATION ROADMAP 21===================== 22 23This file contains the following sections: 24 25OVERVIEW General description of JPEG and the IJG software. 26LEGAL ISSUES Copyright, lack of warranty, terms of distribution. 27REFERENCES Where to learn more about JPEG. 28ARCHIVE LOCATIONS Where to find newer versions of this software. 29ACKNOWLEDGMENTS Special thanks. 30FILE FORMAT WARS Software *not* to get. 31TO DO Plans for future IJG releases. 32 33Other documentation files in the distribution are: 34 35User documentation: 36 install.txt How to configure and install the IJG software. 37 usage.txt Usage instructions for cjpeg, djpeg, jpegtran, 38 rdjpgcom, and wrjpgcom. 39 *.1 Unix-style man pages for programs (same info as usage.txt). 40 wizard.txt Advanced usage instructions for JPEG wizards only. 41 change.log Version-to-version change highlights. 42Programmer and internal documentation: 43 libjpeg.txt How to use the JPEG library in your own programs. 44 example.c Sample code for calling the JPEG library. 45 structure.txt Overview of the JPEG library's internal structure. 46 filelist.txt Road map of IJG files. 47 coderules.txt Coding style rules --- please read if you contribute code. 48 49Please read at least the files install.txt and usage.txt. Some information 50can also be found in the JPEG FAQ (Frequently Asked Questions) article. See 51ARCHIVE LOCATIONS below to find out where to obtain the FAQ article. 52 53If you want to understand how the JPEG code works, we suggest reading one or 54more of the REFERENCES, then looking at the documentation files (in roughly 55the order listed) before diving into the code. 56 57 58OVERVIEW 59======== 60 61This package contains C software to implement JPEG image encoding, decoding, 62and transcoding. JPEG (pronounced "jay-peg") is a standardized compression 63method for full-color and gray-scale images. 64 65This software implements JPEG baseline, extended-sequential, and progressive 66compression processes. Provision is made for supporting all variants of these 67processes, although some uncommon parameter settings aren't implemented yet. 68We have made no provision for supporting the hierarchical or lossless 69processes defined in the standard. 70 71We provide a set of library routines for reading and writing JPEG image files, 72plus two sample applications "cjpeg" and "djpeg", which use the library to 73perform conversion between JPEG and some other popular image file formats. 74The library is intended to be reused in other applications. 75 76In order to support file conversion and viewing software, we have included 77considerable functionality beyond the bare JPEG coding/decoding capability; 78for example, the color quantization modules are not strictly part of JPEG 79decoding, but they are essential for output to colormapped file formats or 80colormapped displays. These extra functions can be compiled out of the 81library if not required for a particular application. 82 83We have also included "jpegtran", a utility for lossless transcoding between 84different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple 85applications for inserting and extracting textual comments in JFIF files. 86 87The emphasis in designing this software has been on achieving portability and 88flexibility, while also making it fast enough to be useful. In particular, 89the software is not intended to be read as a tutorial on JPEG. (See the 90REFERENCES section for introductory material.) Rather, it is intended to 91be reliable, portable, industrial-strength code. We do not claim to have 92achieved that goal in every aspect of the software, but we strive for it. 93 94We welcome the use of this software as a component of commercial products. 95No royalty is required, but we do ask for an acknowledgement in product 96documentation, as described under LEGAL ISSUES. 97 98 99LEGAL ISSUES 100============ 101 102In plain English: 103 1041. We don't promise that this software works. (But if you find any bugs, 105 please let us know!) 1062. You can use this software for whatever you want. You don't have to pay us. 1073. You may not pretend that you wrote this software. If you use it in a 108 program, you must acknowledge somewhere in your documentation that 109 you've used the IJG code. 110 111In legalese: 112 113The authors make NO WARRANTY or representation, either express or implied, 114with respect to this software, its quality, accuracy, merchantability, or 115fitness for a particular purpose. This software is provided "AS IS", and you, 116its user, assume the entire risk as to its quality and accuracy. 117 118This software is copyright (C) 1991-2012, Thomas G. Lane, Guido Vollbeding. 119All Rights Reserved except as specified below. 120 121Permission is hereby granted to use, copy, modify, and distribute this 122software (or portions thereof) for any purpose, without fee, subject to these 123conditions: 124(1) If any part of the source code for this software is distributed, then this 125README file must be included, with this copyright and no-warranty notice 126unaltered; and any additions, deletions, or changes to the original files 127must be clearly indicated in accompanying documentation. 128(2) If only executable code is distributed, then the accompanying 129documentation must state that "this software is based in part on the work of 130the Independent JPEG Group". 131(3) Permission for use of this software is granted only if the user accepts 132full responsibility for any undesirable consequences; the authors accept 133NO LIABILITY for damages of any kind. 134 135These conditions apply to any software derived from or based on the IJG code, 136not just to the unmodified library. If you use our work, you ought to 137acknowledge us. 138 139Permission is NOT granted for the use of any IJG author's name or company name 140in advertising or publicity relating to this software or products derived from 141it. This software may be referred to only as "the Independent JPEG Group's 142software". 143 144We specifically permit and encourage the use of this software as the basis of 145commercial products, provided that all warranty or liability claims are 146assumed by the product vendor. 147 148 149ansi2knr.c is included in this distribution by permission of L. Peter Deutsch, 150sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA. 151ansi2knr.c is NOT covered by the above copyright and conditions, but instead 152by the usual distribution terms of the Free Software Foundation; principally, 153that you must include source code if you redistribute it. (See the file 154ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part 155of any program generated from the IJG code, this does not limit you more than 156the foregoing paragraphs do. 157 158The Unix configuration script "configure" was produced with GNU Autoconf. 159It is copyright by the Free Software Foundation but is freely distributable. 160The same holds for its supporting scripts (config.guess, config.sub, 161ltmain.sh). Another support script, install-sh, is copyright by X Consortium 162but is also freely distributable. 163 164The IJG distribution formerly included code to read and write GIF files. 165To avoid entanglement with the Unisys LZW patent, GIF reading support has 166been removed altogether, and the GIF writer has been simplified to produce 167"uncompressed GIFs". This technique does not use the LZW algorithm; the 168resulting GIF files are larger than usual, but are readable by all standard 169GIF decoders. 170 171We are required to state that 172 "The Graphics Interchange Format(c) is the Copyright property of 173 CompuServe Incorporated. GIF(sm) is a Service Mark property of 174 CompuServe Incorporated." 175 176 177REFERENCES 178========== 179 180We recommend reading one or more of these references before trying to 181understand the innards of the JPEG software. 182 183The best short technical introduction to the JPEG compression algorithm is 184 Wallace, Gregory K. "The JPEG Still Picture Compression Standard", 185 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. 186(Adjacent articles in that issue discuss MPEG motion picture compression, 187applications of JPEG, and related topics.) If you don't have the CACM issue 188handy, a PostScript file containing a revised version of Wallace's article is 189available at http://www.ijg.org/files/wallace.ps.gz. The file (actually 190a preprint for an article that appeared in IEEE Trans. Consumer Electronics) 191omits the sample images that appeared in CACM, but it includes corrections 192and some added material. Note: the Wallace article is copyright ACM and IEEE, 193and it may not be used for commercial purposes. 194 195A somewhat less technical, more leisurely introduction to JPEG can be found in 196"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by 197M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides 198good explanations and example C code for a multitude of compression methods 199including JPEG. It is an excellent source if you are comfortable reading C 200code but don't know much about data compression in general. The book's JPEG 201sample code is far from industrial-strength, but when you are ready to look 202at a full implementation, you've got one here... 203 204The best currently available description of JPEG is the textbook "JPEG Still 205Image Data Compression Standard" by William B. Pennebaker and Joan L. 206Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. 207Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG 208standards (DIS 10918-1 and draft DIS 10918-2). 209Although this is by far the most detailed and comprehensive exposition of 210JPEG publicly available, we point out that it is still missing an explanation 211of the most essential properties and algorithms of the underlying DCT 212technology. 213If you think that you know about DCT-based JPEG after reading this book, 214then you are in delusion. The real fundamentals and corresponding potential 215of DCT-based JPEG are not publicly known so far, and that is the reason for 216all the mistaken developments taking place in the image coding domain. 217 218The original JPEG standard is divided into two parts, Part 1 being the actual 219specification, while Part 2 covers compliance testing methods. Part 1 is 220titled "Digital Compression and Coding of Continuous-tone Still Images, 221Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS 22210918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of 223Continuous-tone Still Images, Part 2: Compliance testing" and has document 224numbers ISO/IEC IS 10918-2, ITU-T T.83. 225IJG JPEG 8 introduces an implementation of the JPEG SmartScale extension 226which is specified in two documents: A contributed document at ITU and ISO 227with title "ITU-T JPEG-Plus Proposal for Extending ITU-T T.81 for Advanced 228Image Coding", April 2006, Geneva, Switzerland. The latest version of this 229document is Revision 3. And a contributed document ISO/IEC JTC1/SC29/WG1 N 2305799 with title "Evolution of JPEG", June/July 2011, Berlin, Germany. 231 232The JPEG standard does not specify all details of an interchangeable file 233format. For the omitted details we follow the "JFIF" conventions, revision 2341.02. JFIF 1.02 has been adopted as an Ecma International Technical Report 235and thus received a formal publication status. It is available as a free 236download in PDF format from 237http://www.ecma-international.org/publications/techreports/E-TR-098.htm. 238A PostScript version of the JFIF document is available at 239http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at 240http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures. 241 242The TIFF 6.0 file format specification can be obtained by FTP from 243ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme 244found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. 245IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). 246Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 247(Compression tag 7). Copies of this Note can be obtained from 248http://www.ijg.org/files/. It is expected that the next revision 249of the TIFF spec will replace the 6.0 JPEG design with the Note's design. 250Although IJG's own code does not support TIFF/JPEG, the free libtiff library 251uses our library to implement TIFF/JPEG per the Note. 252 253 254ARCHIVE LOCATIONS 255================= 256 257The "official" archive site for this software is www.ijg.org. 258The most recent released version can always be found there in 259directory "files". This particular version will be archived as 260http://www.ijg.org/files/jpegsrc.v8d.tar.gz, and in Windows-compatible 261"zip" archive format as http://www.ijg.org/files/jpegsr8d.zip. 262 263The JPEG FAQ (Frequently Asked Questions) article is a source of some 264general information about JPEG. 265It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ 266and other news.answers archive sites, including the official news.answers 267archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. 268If you don't have Web or FTP access, send e-mail to email@example.com 269with body 270 send usenet/news.answers/jpeg-faq/part1 271 send usenet/news.answers/jpeg-faq/part2 272 273 274ACKNOWLEDGMENTS 275=============== 276 277Thank to Juergen Bruder for providing me with a copy of the common DCT 278algorithm article, only to find out that I had come to the same result 279in a more direct and comprehensible way with a more generative approach. 280 281Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the 282ITU JPEG (Study Group 16) meeting in Geneva, Switzerland. 283 284Thank to Thomas Wiegand and Gary Sullivan for inviting me to the 285Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland. 286 287Thank to Thomas Richter and Daniel Lee for inviting me to the 288ISO/IEC JTC1/SC29/WG1 (also known as JPEG, together with ITU-T SG16) 289meeting in Berlin, Germany. 290 291Thank to John Korejwa and Massimo Ballerini for inviting me to 292fruitful consultations in Boston, MA and Milan, Italy. 293 294Thank to Hendrik Elstner, Roland Fassauer, Simone Zuck, Guenther 295Maier-Gerber, Walter Stoeber, Fred Schmitz, and Norbert Braunagel 296for corresponding business development. 297 298Thank to Nico Zschach and Dirk Stelling of the technical support team 299at the Digital Images company in Halle for providing me with extra 300equipment for configuration tests. 301 302Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful 303communication about JPEG configuration in Sigma Photo Pro software. 304 305Thank to Andrew Finkenstadt for hosting the ijg.org site. 306 307Last but not least special thank to Thomas G. Lane for the original 308design and development of this singular software package. 309 310 311FILE FORMAT WARS 312================ 313 314The ISO/IEC JTC1/SC29/WG1 standards committee (also known as JPEG, together 315with ITU-T SG16) currently promotes different formats containing the name 316"JPEG" which is misleading because these formats are incompatible with 317original DCT-based JPEG and are based on faulty technologies. 318IJG therefore does not and will not support such momentary mistakes 319(see REFERENCES). 320There exist also distributions under the name "OpenJPEG" promoting such 321kind of formats which is misleading because they don't support original 322JPEG images. 323We have no sympathy for the promotion of inferior formats. Indeed, one of 324the original reasons for developing this free software was to help force 325convergence on common, interoperable format standards for JPEG files. 326Don't use an incompatible file format! 327(In any case, our decoder will remain capable of reading existing JPEG 328image files indefinitely.) 329 330Furthermore, the ISO committee pretends to be "responsible for the popular 331JPEG" in their public reports which is not true because they don't respond to 332actual requirements for the maintenance of the original JPEG specification. 333 334There are currently distributions in circulation containing the name 335"libjpeg" which claim to be a "derivative" or "fork" of the original 336libjpeg, but don't have the features and are incompatible with formats 337supported by actual IJG libjpeg distributions. Furthermore, they 338violate the license conditions as described under LEGAL ISSUES above. 339We have no sympathy for the release of misleading and illegal 340distributions derived from obsolete code bases. 341Don't use an obsolete code base! 342 343 344TO DO 345===== 346 347Version 8 is the first release of a new generation JPEG standard 348to overcome the limitations of the original JPEG specification. 349More features are being prepared for coming releases... 350 351Please send bug reports, offers of help, etc. to firstname.lastname@example.org.