1 The Independent JPEG Group's JPEG software 2 ========================================== 3 4 README for release 7 of 27-Jun-2009 5 =================================== 6 7 This distribution contains the seventh public release of the Independent JPEG 8 Group's free JPEG software. You are welcome to redistribute this software and 9 to use it for any purpose, subject to the conditions under LEGAL ISSUES, below. 10 11 This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone, 12 Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson, 13 Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers, 14 and other members of the Independent JPEG Group. 15 16 IJG is not affiliated with the official ISO JPEG standards committee. 17 18 19 DOCUMENTATION ROADMAP 20 ===================== 21 22 This file contains the following sections: 23 24 OVERVIEW General description of JPEG and the IJG software. 25 LEGAL ISSUES Copyright, lack of warranty, terms of distribution. 26 REFERENCES Where to learn more about JPEG. 27 ARCHIVE LOCATIONS Where to find newer versions of this software. 28 ACKNOWLEDGMENTS Special thanks. 29 FILE FORMAT WARS Software *not* to get. 30 TO DO Plans for future IJG releases. 31 32 Other documentation files in the distribution are: 33 34 User 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. 41 Programmer 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 48 Please read at least the files install.txt and usage.txt. Some information 49 can also be found in the JPEG FAQ (Frequently Asked Questions) article. See 50 ARCHIVE LOCATIONS below to find out where to obtain the FAQ article. 51 52 If you want to understand how the JPEG code works, we suggest reading one or 53 more of the REFERENCES, then looking at the documentation files (in roughly 54 the order listed) before diving into the code. 55 56 57 OVERVIEW 58 ======== 59 60 This package contains C software to implement JPEG image encoding, decoding, 61 and transcoding. JPEG (pronounced "jay-peg") is a standardized compression 62 method for full-color and gray-scale images. 63 64 This software implements JPEG baseline, extended-sequential, and progressive 65 compression processes. Provision is made for supporting all variants of these 66 processes, although some uncommon parameter settings aren't implemented yet. 67 We have made no provision for supporting the hierarchical or lossless 68 processes defined in the standard. 69 70 We provide a set of library routines for reading and writing JPEG image files, 71 plus two sample applications "cjpeg" and "djpeg", which use the library to 72 perform conversion between JPEG and some other popular image file formats. 73 The library is intended to be reused in other applications. 74 75 In order to support file conversion and viewing software, we have included 76 considerable functionality beyond the bare JPEG coding/decoding capability; 77 for example, the color quantization modules are not strictly part of JPEG 78 decoding, but they are essential for output to colormapped file formats or 79 colormapped displays. These extra functions can be compiled out of the 80 library if not required for a particular application. 81 82 We have also included "jpegtran", a utility for lossless transcoding between 83 different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple 84 applications for inserting and extracting textual comments in JFIF files. 85 86 The emphasis in designing this software has been on achieving portability and 87 flexibility, while also making it fast enough to be useful. In particular, 88 the software is not intended to be read as a tutorial on JPEG. (See the 89 REFERENCES section for introductory material.) Rather, it is intended to 90 be reliable, portable, industrial-strength code. We do not claim to have 91 achieved that goal in every aspect of the software, but we strive for it. 92 93 We welcome the use of this software as a component of commercial products. 94 No royalty is required, but we do ask for an acknowledgement in product 95 documentation, as described under LEGAL ISSUES. 96 97 98 LEGAL ISSUES 99 ============ 100 101 In plain English: 102 103 1. We don't promise that this software works. (But if you find any bugs, 104 please let us know!) 105 2. You can use this software for whatever you want. You don't have to pay us. 106 3. 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. 109 110 In legalese: 111 112 The authors make NO WARRANTY or representation, either express or implied, 113 with respect to this software, its quality, accuracy, merchantability, or 114 fitness for a particular purpose. This software is provided "AS IS", and you, 115 its user, assume the entire risk as to its quality and accuracy. 116 117 This software is copyright (C) 1991-2009, Thomas G. Lane, Guido Vollbeding. 118 All Rights Reserved except as specified below. 119 120 Permission is hereby granted to use, copy, modify, and distribute this 121 software (or portions thereof) for any purpose, without fee, subject to these 122 conditions: 123 (1) If any part of the source code for this software is distributed, then this 124 README file must be included, with this copyright and no-warranty notice 125 unaltered; and any additions, deletions, or changes to the original files 126 must be clearly indicated in accompanying documentation. 127 (2) If only executable code is distributed, then the accompanying 128 documentation must state that "this software is based in part on the work of 129 the Independent JPEG Group". 130 (3) Permission for use of this software is granted only if the user accepts 131 full responsibility for any undesirable consequences; the authors accept 132 NO LIABILITY for damages of any kind. 133 134 These conditions apply to any software derived from or based on the IJG code, 135 not just to the unmodified library. If you use our work, you ought to 136 acknowledge us. 137 138 Permission is NOT granted for the use of any IJG author's name or company name 139 in advertising or publicity relating to this software or products derived from 140 it. This software may be referred to only as "the Independent JPEG Group's 141 software". 142 143 We specifically permit and encourage the use of this software as the basis of 144 commercial products, provided that all warranty or liability claims are 145 assumed by the product vendor. 146 147 148 ansi2knr.c is included in this distribution by permission of L. Peter Deutsch, 149 sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA. 150 ansi2knr.c is NOT covered by the above copyright and conditions, but instead 151 by the usual distribution terms of the Free Software Foundation; principally, 152 that you must include source code if you redistribute it. (See the file 153 ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part 154 of any program generated from the IJG code, this does not limit you more than 155 the foregoing paragraphs do. 156 157 The Unix configuration script "configure" was produced with GNU Autoconf. 158 It is copyright by the Free Software Foundation but is freely distributable. 159 The same holds for its supporting scripts (config.guess, config.sub, 160 ltmain.sh). Another support script, install-sh, is copyright by X Consortium 161 but is also freely distributable. 162 163 The IJG distribution formerly included code to read and write GIF files. 164 To avoid entanglement with the Unisys LZW patent, GIF reading support has 165 been removed altogether, and the GIF writer has been simplified to produce 166 "uncompressed GIFs". This technique does not use the LZW algorithm; the 167 resulting GIF files are larger than usual, but are readable by all standard 168 GIF decoders. 169 170 We 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." 174 175 176 REFERENCES 177 ========== 178 179 We recommend reading one or more of these references before trying to 180 understand the innards of the JPEG software. 181 182 The 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, 186 applications of JPEG, and related topics.) If you don't have the CACM issue 187 handy, a PostScript file containing a revised version of Wallace's article is 188 available at http://www.ijg.org/files/wallace.ps.gz. The file (actually 189 a preprint for an article that appeared in IEEE Trans. Consumer Electronics) 190 omits the sample images that appeared in CACM, but it includes corrections 191 and some added material. Note: the Wallace article is copyright ACM and IEEE, 192 and it may not be used for commercial purposes. 193 194 A 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 196 M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides 197 good explanations and example C code for a multitude of compression methods 198 including JPEG. It is an excellent source if you are comfortable reading C 199 code but don't know much about data compression in general. The book's JPEG 200 sample code is far from industrial-strength, but when you are ready to look 201 at a full implementation, you've got one here... 202 203 The best currently available description of JPEG is the textbook "JPEG Still 204 Image Data Compression Standard" by William B. Pennebaker and Joan L. 205 Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. 206 Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG 207 standards (DIS 10918-1 and draft DIS 10918-2). 208 Although this is by far the most detailed and comprehensive exposition of 209 JPEG publicly available, we point out that it is still missing an explanation 210 of the most essential properties and algorithms of the underlying DCT 211 technology. 212 If you think that you know about DCT-based JPEG after reading this book, 213 then you are in delusion. The real fundamentals and corresponding potential 214 of DCT-based JPEG are not publicly known so far, and that is the reason for 215 all the mistaken developments taking place in the image coding domain. 216 217 The original JPEG standard is divided into two parts, Part 1 being the actual 218 specification, while Part 2 covers compliance testing methods. Part 1 is 219 titled "Digital Compression and Coding of Continuous-tone Still Images, 220 Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS 221 10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of 222 Continuous-tone Still Images, Part 2: Compliance testing" and has document 223 numbers ISO/IEC IS 10918-2, ITU-T T.83. 224 225 The JPEG standard does not specify all details of an interchangeable file 226 format. For the omitted details we follow the "JFIF" conventions, revision 227 1.02. A copy of the JFIF spec is available from: 228 Literature Department 229 C-Cube Microsystems, Inc. 230 1778 McCarthy Blvd. 231 Milpitas, CA 95035 232 phone (408) 944-6300, fax (408) 944-6314 233 A PostScript version of this document is available at 234 http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at 235 http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures. 236 237 The TIFF 6.0 file format specification can be obtained by FTP from 238 ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme 239 found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. 240 IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). 241 Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 242 (Compression tag 7). Copies of this Note can be obtained from 243 http://www.ijg.org/files/. It is expected that the next revision 244 of the TIFF spec will replace the 6.0 JPEG design with the Note's design. 245 Although IJG's own code does not support TIFF/JPEG, the free libtiff library 246 uses our library to implement TIFF/JPEG per the Note. 247 248 249 ARCHIVE LOCATIONS 250 ================= 251 252 The "official" archive site for this software is www.ijg.org. 253 The most recent released version can always be found there in 254 directory "files". This particular version will be archived as 255 http://www.ijg.org/files/jpegsrc.v7.tar.gz, and in Windows-compatible 256 "zip" archive format as http://www.ijg.org/files/jpegsr7.zip. 257 258 The JPEG FAQ (Frequently Asked Questions) article is a source of some 259 general information about JPEG. 260 It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ 261 and other news.answers archive sites, including the official news.answers 262 archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. 263 If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu 264 with body 265 send usenet/news.answers/jpeg-faq/part1 266 send usenet/news.answers/jpeg-faq/part2 267 268 269 ACKNOWLEDGMENTS 270 =============== 271 272 Thank to Juergen Bruder of the Georg-Cantor-Organization at the 273 Martin-Luther-University Halle for providing me with a copy of the common 274 DCT algorithm article, only to find out that I had come to the same result 275 in a more direct and comprehensible way with a more generative approach. 276 277 Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the 278 ITU JPEG (Study Group 16) meeting in Geneva, Switzerland. 279 280 Thank to Thomas Wiegand and Gary Sullivan for inviting me to the 281 Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland. 282 283 Thank to John Korejwa and Massimo Ballerini for inviting me to 284 fruitful consultations in Boston, MA and Milan, Italy. 285 286 Thank to Hendrik Elstner, Roland Fassauer, and Simone Zuck for 287 corresponding business development. 288 289 Thank to Nico Zschach and Dirk Stelling of the technical support team 290 at the Digital Images company in Halle for providing me with extra 291 equipment for configuration tests. 292 293 Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful 294 communication about JPEG configuration in Sigma Photo Pro software. 295 296 Last but not least special thank to Thomas G. Lane for the original 297 design and development of this singular software package. 298 299 300 FILE FORMAT WARS 301 ================ 302 303 The ISO JPEG standards committee actually promotes different formats like 304 JPEG-2000 or JPEG-XR which are incompatible with original DCT-based JPEG 305 and which are based on faulty technologies. IJG therefore does not and 306 will not support such momentary mistakes (see REFERENCES). 307 We have little or no sympathy for the promotion of these formats. Indeed, 308 one of the original reasons for developing this free software was to help 309 force convergence on common, interoperable format standards for JPEG files. 310 Don't use an incompatible file format! 311 (In any case, our decoder will remain capable of reading existing JPEG 312 image files indefinitely.) 313 314 315 TO DO 316 ===== 317 318 v7 is basically just a necessary interim release, paving the way for a 319 major breakthrough in image coding technology with the next v8 package 320 which is scheduled for release in the year 2010. 321 322 Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org.