1The Independent JPEG Group's JPEG software 2========================================== 3 4README for release 9d of 12-Jan-2020 5==================================== 6 7This distribution contains the ninth 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, 13John Korejwa, Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, 14Ge' Weijers, and other members of the Independent JPEG Group. 15 16IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee 17(previously 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 grayscale 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) 1991-2020, 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 149The Unix configuration script "configure" was produced with GNU Autoconf. 150It is copyright by the Free Software Foundation but is freely distributable. 151The same holds for its supporting scripts (config.guess, config.sub, 152ltmain.sh). Another support script, install-sh, is copyright by X Consortium 153but is also freely distributable. 154 155 156REFERENCES 157========== 158 159We recommend reading one or more of these references before trying to 160understand the innards of the JPEG software. 161 162The best short technical introduction to the JPEG compression algorithm is 163 Wallace, Gregory K. "The JPEG Still Picture Compression Standard", 164 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. 165(Adjacent articles in that issue discuss MPEG motion picture compression, 166applications of JPEG, and related topics.) If you don't have the CACM issue 167handy, a PDF file containing a revised version of Wallace's article is 168available at http://www.ijg.org/files/Wallace.JPEG.pdf. The file (actually 169a preprint for an article that appeared in IEEE Trans. Consumer Electronics) 170omits the sample images that appeared in CACM, but it includes corrections 171and some added material. Note: the Wallace article is copyright ACM and IEEE, 172and it may not be used for commercial purposes. 173 174A somewhat less technical, more leisurely introduction to JPEG can be found in 175"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by 176M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides 177good explanations and example C code for a multitude of compression methods 178including JPEG. It is an excellent source if you are comfortable reading C 179code but don't know much about data compression in general. The book's JPEG 180sample code is far from industrial-strength, but when you are ready to look 181at a full implementation, you've got one here... 182 183The best currently available description of JPEG is the textbook "JPEG Still 184Image Data Compression Standard" by William B. Pennebaker and Joan L. 185Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. 186Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG 187standards (DIS 10918-1 and draft DIS 10918-2). 188Although this is by far the most detailed and comprehensive exposition of 189JPEG publicly available, we point out that it is still missing an explanation 190of the most essential properties and algorithms of the underlying DCT 191technology. 192If you think that you know about DCT-based JPEG after reading this book, 193then you are in delusion. The real fundamentals and corresponding potential 194of DCT-based JPEG are not publicly known so far, and that is the reason for 195all the mistaken developments taking place in the image coding domain. 196 197The original JPEG standard is divided into two parts, Part 1 being the actual 198specification, while Part 2 covers compliance testing methods. Part 1 is 199titled "Digital Compression and Coding of Continuous-tone Still Images, 200Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS 20110918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of 202Continuous-tone Still Images, Part 2: Compliance testing" and has document 203numbers ISO/IEC IS 10918-2, ITU-T T.83. 204IJG JPEG 8 introduced an implementation of the JPEG SmartScale extension 205which is specified in two documents: A contributed document at ITU and ISO 206with title "ITU-T JPEG-Plus Proposal for Extending ITU-T T.81 for Advanced 207Image Coding", April 2006, Geneva, Switzerland. The latest version of this 208document is Revision 3. And a contributed document ISO/IEC JTC1/SC29/WG1 N 2095799 with title "Evolution of JPEG", June/July 2011, Berlin, Germany. 210IJG JPEG 9 introduces a reversible color transform for improved lossless 211compression which is described in a contributed document ISO/IEC JTC1/SC29/ 212WG1 N 6080 with title "JPEG 9 Lossless Coding", June/July 2012, Paris, 213France. 214 215The JPEG standard does not specify all details of an interchangeable file 216format. For the omitted details we follow the "JFIF" conventions, version 2. 217JFIF version 1 has been adopted as Recommendation ITU-T T.871 (05/2011) : 218Information technology - Digital compression and coding of continuous-tone 219still images: JPEG File Interchange Format (JFIF). It is available as a 220free download in PDF file format from http://www.itu.int/rec/T-REC-T.871. 221A PDF file of the older JFIF document is available at 222http://www.w3.org/Graphics/JPEG/jfif3.pdf. 223 224The TIFF 6.0 file format specification can be obtained by FTP from 225ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme 226found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. 227IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). 228Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 229(Compression tag 7). Copies of this Note can be obtained from 230http://www.ijg.org/files/. It is expected that the next revision 231of the TIFF spec will replace the 6.0 JPEG design with the Note's design. 232Although IJG's own code does not support TIFF/JPEG, the free libtiff library 233uses our library to implement TIFF/JPEG per the Note. 234 235 236ARCHIVE LOCATIONS 237================= 238 239The "official" archive site for this software is www.ijg.org. 240The most recent released version can always be found there in 241directory "files". This particular version will be archived as 242http://www.ijg.org/files/jpegsrc.v9d.tar.gz, and in Windows-compatible 243"zip" archive format as http://www.ijg.org/files/jpegsr9d.zip. 244 245The JPEG FAQ (Frequently Asked Questions) article is a source of some 246general information about JPEG. 247It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ 248and other news.answers archive sites, including the official news.answers 249archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. 250If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu 251with body 252 send usenet/news.answers/jpeg-faq/part1 253 send usenet/news.answers/jpeg-faq/part2 254 255 256ACKNOWLEDGMENTS 257=============== 258 259Thank to Juergen Bruder for providing me with a copy of the common DCT 260algorithm article, only to find out that I had come to the same result 261in a more direct and comprehensible way with a more generative approach. 262 263Thank to Istvan Sebestyen and Joan L. Mitchell for inviting me to the 264ITU JPEG (Study Group 16) meeting in Geneva, Switzerland. 265 266Thank to Thomas Wiegand and Gary Sullivan for inviting me to the 267Joint Video Team (MPEG & ITU) meeting in Geneva, Switzerland. 268 269Thank to Thomas Richter and Daniel Lee for inviting me to the 270ISO/IEC JTC1/SC29/WG1 (previously known as JPEG, together with ITU-T SG16) 271meeting in Berlin, Germany. 272 273Thank to John Korejwa and Massimo Ballerini for inviting me to 274fruitful consultations in Boston, MA and Milan, Italy. 275 276Thank to Hendrik Elstner, Roland Fassauer, Simone Zuck, Guenther 277Maier-Gerber, Walter Stoeber, Fred Schmitz, and Norbert Braunagel 278for corresponding business development. 279 280Thank to Nico Zschach and Dirk Stelling of the technical support team 281at the Digital Images company in Halle for providing me with extra 282equipment for configuration tests. 283 284Thank to Richard F. Lyon (then of Foveon Inc.) for fruitful 285communication about JPEG configuration in Sigma Photo Pro software. 286 287Thank to Andrew Finkenstadt for hosting the ijg.org site. 288 289Thank to Thomas G. Lane for the original design and development of 290this singular software package. 291 292Thank to Lars Goehler, Andreas Heinecke, Sebastian Fuss, Yvonne Roebert, 293Andrej Werner, and Ulf-Dietrich Braumann for support and public relations. 294 295 296FILE FORMAT WARS 297================ 298 299The ISO/IEC JTC1/SC29/WG1 standards committee (previously known as JPEG, 300together with ITU-T SG16) currently promotes different formats containing 301the name "JPEG" which is misleading because these formats are incompatible 302with original DCT-based JPEG and are based on faulty technologies. 303IJG therefore does not and will not support such momentary mistakes 304(see REFERENCES). 305There exist also distributions under the name "OpenJPEG" promoting such 306kind of formats which is misleading because they don't support original 307JPEG images. 308We have no sympathy for the promotion of inferior formats. Indeed, one of 309the original reasons for developing this free software was to help force 310convergence on common, interoperable format standards for JPEG files. 311Don't use an incompatible file format! 312(In any case, our decoder will remain capable of reading existing JPEG 313image files indefinitely.) 314 315The ISO committee pretends to be "responsible for the popular JPEG" in their 316public reports which is not true because they don't respond to actual 317requirements for the maintenance of the original JPEG specification. 318Furthermore, the ISO committee pretends to "ensure interoperability" with 319their standards which is not true because their "standards" support only 320application-specific and proprietary use cases and contain mathematically 321incorrect code. 322 323There are currently different distributions in circulation containing the 324name "libjpeg" which is misleading because they don't have the features and 325are incompatible with formats supported by actual IJG libjpeg distributions. 326One of those fakes is released by members of the ISO committee and just uses 327the name of libjpeg for misdirection of people, similar to the abuse of the 328name JPEG as described above, while having nothing in common with actual IJG 329libjpeg distributions and containing mathematically incorrect code. 330The other one claims to be a "derivative" or "fork" of the original libjpeg, 331but violates the license conditions as described under LEGAL ISSUES above 332and violates basic C programming properties. 333We have no sympathy for the release of misleading, incorrect and illegal 334distributions derived from obsolete code bases. 335Don't use an obsolete code base! 336 337According to the UCC (Uniform Commercial Code) law, IJG has the lawful and 338legal right to foreclose on certain standardization bodies and other 339institutions or corporations that knowingly perform substantial and 340systematic deceptive acts and practices, fraud, theft, and damaging of the 341value of the people of this planet without their knowing, willing and 342intentional consent. 343The titles, ownership, and rights of these institutions and all their assets 344are now duly secured and held in trust for the free people of this planet. 345People of the planet, on every country, may have a financial interest in 346the assets of these former principals, agents, and beneficiaries of the 347foreclosed institutions and corporations. 348IJG asserts what is: that each man, woman, and child has unalienable value 349and rights granted and deposited in them by the Creator and not any one of 350the people is subordinate to any artificial principality, corporate fiction 351or the special interest of another without their appropriate knowing, 352willing and intentional consent made by contract or accommodation agreement. 353IJG expresses that which already was. 354The people have already determined and demanded that public administration 355entities, national governments, and their supporting judicial systems must 356be fully transparent, accountable, and liable. 357IJG has secured the value for all concerned free people of the planet. 358 359A partial list of foreclosed institutions and corporations ("Hall of Shame") 360is currently prepared and will be published later. 361 362 363TO DO 364===== 365 366Version 9 is the second release of a new generation JPEG standard 367to overcome the limitations of the original JPEG specification, 368and is the first true source reference JPEG codec. 369More features are being prepared for coming releases... 370 371Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org. 372
