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1The Independent JPEG Group's JPEG software 2========================================== 3 4README for release 8b of 16-May-2010 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 official ISO JPEG standards committee. 17 18 19DOCUMENTATION ROADMAP 20===================== 21 22This file contains the following sections: 23 24OVERVIEW General description of JPEG and the IJG software. 25LEGAL ISSUES Copyright, lack of warranty, terms of distribution. 26REFERENCES Where to learn more about JPEG. 27ARCHIVE LOCATIONS Where to find newer versions of this software. 28ACKNOWLEDGMENTS Special thanks. 29FILE FORMAT WARS Software *not* to get. 30TO DO Plans for future IJG releases. 31 32Other documentation files in the distribution are: 33 34User documentation: 35 install.txt How to configure and install the IJG software. 36 usage.txt Usage instructions for cjpeg, djpeg, jpegtran, 37 rdjpgcom, and wrjpgcom. 38 *.1 Unix-style man pages for programs (same info as usage.txt). 39 wizard.txt Advanced usage instructions for JPEG wizards only. 40 change.log Version-to-version change highlights. 41Programmer and internal documentation: 42 libjpeg.txt How to use the JPEG library in your own programs. 43 example.c Sample code for calling the JPEG library. 44 structure.txt Overview of the JPEG library's internal structure. 45 filelist.txt Road map of IJG files. 46 coderules.txt Coding style rules --- please read if you contribute code. 47 48Please read at least the files install.txt and usage.txt. Some information 49can also be found in the JPEG FAQ (Frequently Asked Questions) article. See 50ARCHIVE LOCATIONS below to find out where to obtain the FAQ article. 51 52If you want to understand how the JPEG code works, we suggest reading one or 53more of the REFERENCES, then looking at the documentation files (in roughly 54the order listed) before diving into the code. 55 56 57OVERVIEW 58======== 59 60This package contains C software to implement JPEG image encoding, decoding, 61and transcoding. JPEG (pronounced "jay-peg") is a standardized compression 62method for full-color and gray-scale images. 63 64This software implements JPEG baseline, extended-sequential, and progressive 65compression processes. Provision is made for supporting all variants of these 66processes, although some uncommon parameter settings aren't implemented yet. 67We have made no provision for supporting the hierarchical or lossless 68processes defined in the standard. 69 70We provide a set of library routines for reading and writing JPEG image files, 71plus two sample applications "cjpeg" and "djpeg", which use the library to 72perform conversion between JPEG and some other popular image file formats. 73The library is intended to be reused in other applications. 74 75In order to support file conversion and viewing software, we have included 76considerable functionality beyond the bare JPEG coding/decoding capability; 77for example, the color quantization modules are not strictly part of JPEG 78decoding, but they are essential for output to colormapped file formats or 79colormapped displays. These extra functions can be compiled out of the 80library if not required for a particular application. 81 82We have also included "jpegtran", a utility for lossless transcoding between 83different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple 84applications for inserting and extracting textual comments in JFIF files. 85 86The emphasis in designing this software has been on achieving portability and 87flexibility, while also making it fast enough to be useful. In particular, 88the software is not intended to be read as a tutorial on JPEG. (See the 89REFERENCES section for introductory material.) Rather, it is intended to 90be reliable, portable, industrial-strength code. We do not claim to have 91achieved that goal in every aspect of the software, but we strive for it. 92 93We welcome the use of this software as a component of commercial products. 94No royalty is required, but we do ask for an acknowledgement in product 95documentation, as described under LEGAL ISSUES. 96 97 98LEGAL ISSUES 99============ 100 101In plain English: 102 1031. We don't promise that this software works. (But if you find any bugs, 104 please let us know!) 1052. You can use this software for whatever you want. You don't have to pay us. 1063. You may not pretend that you wrote this software. If you use it in a 107 program, you must acknowledge somewhere in your documentation that 108 you've used the IJG code. 109 110In legalese: 111 112The authors make NO WARRANTY or representation, either express or implied, 113with respect to this software, its quality, accuracy, merchantability, or 114fitness for a particular purpose. This software is provided "AS IS", and you, 115its user, assume the entire risk as to its quality and accuracy. 116 117This software is copyright (C) 1991-2010, Thomas G. Lane, Guido Vollbeding. 118All Rights Reserved except as specified below. 119 120Permission is hereby granted to use, copy, modify, and distribute this 121software (or portions thereof) for any purpose, without fee, subject to these 122conditions: 123(1) If any part of the source code for this software is distributed, then this 124README file must be included, with this copyright and no-warranty notice 125unaltered; and any additions, deletions, or changes to the original files 126must be clearly indicated in accompanying documentation. 127(2) If only executable code is distributed, then the accompanying 128documentation must state that "this software is based in part on the work of 129the Independent JPEG Group". 130(3) Permission for use of this software is granted only if the user accepts 131full responsibility for any undesirable consequences; the authors accept 132NO LIABILITY for damages of any kind. 133 134These conditions apply to any software derived from or based on the IJG code, 135not just to the unmodified library. If you use our work, you ought to 136acknowledge us. 137 138Permission is NOT granted for the use of any IJG author's name or company name 139in advertising or publicity relating to this software or products derived from 140it. This software may be referred to only as "the Independent JPEG Group's 141software". 142 143We specifically permit and encourage the use of this software as the basis of 144commercial products, provided that all warranty or liability claims are 145assumed by the product vendor. 146 147 148ansi2knr.c is included in this distribution by permission of L. Peter Deutsch, 149sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA. 150ansi2knr.c is NOT covered by the above copyright and conditions, but instead 151by the usual distribution terms of the Free Software Foundation; principally, 152that you must include source code if you redistribute it. (See the file 153ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part 154of any program generated from the IJG code, this does not limit you more than 155the foregoing paragraphs do. 156 157The Unix configuration script "configure" was produced with GNU Autoconf. 158It is copyright by the Free Software Foundation but is freely distributable. 159The same holds for its supporting scripts (config.guess, config.sub, 160ltmain.sh). Another support script, install-sh, is copyright by X Consortium 161but is also freely distributable. 162 163The IJG distribution formerly included code to read and write GIF files. 164To avoid entanglement with the Unisys LZW patent, GIF reading support has 165been removed altogether, and the GIF writer has been simplified to produce 166"uncompressed GIFs". This technique does not use the LZW algorithm; the 167resulting GIF files are larger than usual, but are readable by all standard 168GIF decoders. 169 170We are required to state that 171 "The Graphics Interchange Format(c) is the Copyright property of 172 CompuServe Incorporated. GIF(sm) is a Service Mark property of 173 CompuServe Incorporated." 174 175 176REFERENCES 177========== 178 179We recommend reading one or more of these references before trying to 180understand the innards of the JPEG software. 181 182The best short technical introduction to the JPEG compression algorithm is 183 Wallace, Gregory K. "The JPEG Still Picture Compression Standard", 184 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. 185(Adjacent articles in that issue discuss MPEG motion picture compression, 186applications of JPEG, and related topics.) If you don't have the CACM issue 187handy, a PostScript file containing a revised version of Wallace's article is 188available at http://www.ijg.org/files/wallace.ps.gz. The file (actually 189a preprint for an article that appeared in IEEE Trans. Consumer Electronics) 190omits the sample images that appeared in CACM, but it includes corrections 191and some added material. Note: the Wallace article is copyright ACM and IEEE, 192and it may not be used for commercial purposes. 193 194A somewhat less technical, more leisurely introduction to JPEG can be found in 195"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by 196M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides 197good explanations and example C code for a multitude of compression methods 198including JPEG. It is an excellent source if you are comfortable reading C 199code but don't know much about data compression in general. The book's JPEG 200sample code is far from industrial-strength, but when you are ready to look 201at a full implementation, you've got one here... 202 203The best currently available description of JPEG is the textbook "JPEG Still 204Image Data Compression Standard" by William B. Pennebaker and Joan L. 205Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. 206Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG 207standards (DIS 10918-1 and draft DIS 10918-2). 208Although this is by far the most detailed and comprehensive exposition of 209JPEG publicly available, we point out that it is still missing an explanation 210of the most essential properties and algorithms of the underlying DCT 211technology. 212If you think that you know about DCT-based JPEG after reading this book, 213then you are in delusion. The real fundamentals and corresponding potential 214of DCT-based JPEG are not publicly known so far, and that is the reason for 215all the mistaken developments taking place in the image coding domain. 216 217The original JPEG standard is divided into two parts, Part 1 being the actual 218specification, while Part 2 covers compliance testing methods. Part 1 is 219titled "Digital Compression and Coding of Continuous-tone Still Images, 220Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS 22110918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of 222Continuous-tone Still Images, Part 2: Compliance testing" and has document 223numbers ISO/IEC IS 10918-2, ITU-T T.83. 224IJG JPEG 8 introduces an implementation of the JPEG SmartScale extension 225which is specified in a contributed document at ITU and ISO with title "ITU-T 226JPEG-Plus Proposal for Extending ITU-T T.81 for Advanced Image Coding", April 2272006, Geneva, Switzerland. The latest version of the document is Revision 3. 228 229The JPEG standard does not specify all details of an interchangeable file 230format. For the omitted details we follow the "JFIF" conventions, revision 2311.02. JFIF 1.02 has been adopted as an Ecma International Technical Report 232and thus received a formal publication status. It is available as a free 233download in PDF format from 234http://www.ecma-international.org/publications/techreports/E-TR-098.htm. 235A PostScript version of the JFIF document is available at 236http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at 237http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures. 238 239The TIFF 6.0 file format specification can be obtained by FTP from 240ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme 241found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. 242IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). 243Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 244(Compression tag 7). Copies of this Note can be obtained from 245http://www.ijg.org/files/. It is expected that the next revision 246of the TIFF spec will replace the 6.0 JPEG design with the Note's design. 247Although IJG's own code does not support TIFF/JPEG, the free libtiff library 248uses our library to implement TIFF/JPEG per the Note. 249 250 251ARCHIVE LOCATIONS 252================= 253 254The "official" archive site for this software is www.ijg.org. 255The most recent released version can always be found there in 256directory "files". This particular version will be archived as 257http://www.ijg.org/files/jpegsrc.v8b.tar.gz, and in Windows-compatible 258"zip" archive format as http://www.ijg.org/files/jpegsr8b.zip. 259 260The JPEG FAQ (Frequently Asked Questions) article is a source of some 261general information about JPEG. 262It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ 263and other news.answers archive sites, including the official news.answers 264archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. 265If you don't have Web or FTP access, send e-mail to email@example.com 266with body 267 send usenet/news.answers/jpeg-faq/part1 268 send usenet/news.answers/jpeg-faq/part2 269 270 271ACKNOWLEDGMENTS 272=============== 273 274Thank to Juergen Bruder for providing me with a copy of the common DCT 275algorithm article, only to find out that I had come to the same result 276in a more direct and comprehensible way with a more generative approach. 277 278Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the 279ITU JPEG (Study Group 16) meeting in Geneva, Switzerland. 280 281Thank to Thomas Wiegand and Gary Sullivan for inviting me to the 282Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland. 283 284Thank to John Korejwa and Massimo Ballerini for inviting me to 285fruitful consultations in Boston, MA and Milan, Italy. 286 287Thank to Hendrik Elstner, Roland Fassauer, Simone Zuck, Guenther 288Maier-Gerber, Walter Stoeber, and Fred Schmitz for corresponding 289business development. 290 291Thank to Nico Zschach and Dirk Stelling of the technical support team 292at the Digital Images company in Halle for providing me with extra 293equipment for configuration tests. 294 295Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful 296communication about JPEG configuration in Sigma Photo Pro software. 297 298Thank to Andrew Finkenstadt for hosting the ijg.org site. 299 300Last but not least special thank to Thomas G. Lane for the original 301design and development of this singular software package. 302 303 304FILE FORMAT WARS 305================ 306 307The ISO JPEG standards committee actually promotes different formats like 308"JPEG 2000" or "JPEG XR" which are incompatible with original DCT-based 309JPEG and which are based on faulty technologies. IJG therefore does not 310and will not support such momentary mistakes (see REFERENCES). 311We have little or no sympathy for the promotion of these formats. Indeed, 312one of the original reasons for developing this free software was to help 313force convergence on common, interoperable format standards for JPEG files. 314Don't use an incompatible file format! 315(In any case, our decoder will remain capable of reading existing JPEG 316image files indefinitely.) 317 318 319TO DO 320===== 321 322Version 8 is the first release of a new generation JPEG standard 323to overcome the limitations of the original JPEG specification. 324More features are being prepared for coming releases... 325 326Please send bug reports, offers of help, etc. to firstname.lastname@example.org.