1libjpeg-turbo note: This file has been modified by The libjpeg-turbo Project 2to include only information relevant to libjpeg-turbo, to wordsmith certain 3sections, and to remove impolitic language that existed in the libjpeg v8 4README. It is included only for reference. Please see README-turbo.txt for 5information specific to libjpeg-turbo. 6 7 8The Independent JPEG Group's JPEG software 9========================================== 10 11This distribution contains a release of the Independent JPEG Group's free JPEG 12software. You are welcome to redistribute this software and to use it for any 13purpose, subject to the conditions under LEGAL ISSUES, below. 14 15This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone, 16Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson, 17Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers, 18and other members of the Independent JPEG Group. 19 20IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee 21(also known as JPEG, together with ITU-T SG16). 22 23 24DOCUMENTATION ROADMAP 25===================== 26 27This file contains the following sections: 28 29OVERVIEW General description of JPEG and the IJG software. 30LEGAL ISSUES Copyright, lack of warranty, terms of distribution. 31REFERENCES Where to learn more about JPEG. 32ARCHIVE LOCATIONS Where to find newer versions of this software. 33FILE FORMAT WARS Software *not* to get. 34TO DO Plans for future IJG releases. 35 36Other documentation files in the distribution are: 37 38User documentation: 39 usage.txt Usage instructions for cjpeg, djpeg, jpegtran, 40 rdjpgcom, and wrjpgcom. 41 *.1 Unix-style man pages for programs (same info as usage.txt). 42 wizard.txt Advanced usage instructions for JPEG wizards only. 43 change.log Version-to-version change highlights. 44Programmer and internal documentation: 45 libjpeg.txt How to use the JPEG library in your own programs. 46 example.c Sample code for calling the JPEG library. 47 structure.txt Overview of the JPEG library's internal structure. 48 coderules.txt Coding style rules --- please read if you contribute code. 49 50Please read at least usage.txt. Some information can also be found in the JPEG 51FAQ (Frequently Asked Questions) article. See ARCHIVE LOCATIONS below to find 52out where to obtain the FAQ article. 53 54If you want to understand how the JPEG code works, we suggest reading one or 55more of the REFERENCES, then looking at the documentation files (in roughly 56the order listed) before diving into the code. 57 58 59OVERVIEW 60======== 61 62This package contains C software to implement JPEG image encoding, decoding, 63and transcoding. JPEG (pronounced "jay-peg") is a standardized compression 64method for full-color and grayscale images. JPEG's strong suit is compressing 65photographic images or other types of images that have smooth color and 66brightness transitions between neighboring pixels. Images with sharp lines or 67other abrupt features may not compress well with JPEG, and a higher JPEG 68quality may have to be used to avoid visible compression artifacts with such 69images. 70 71JPEG is lossy, meaning that the output pixels are not necessarily identical to 72the input pixels. However, on photographic content and other "smooth" images, 73very good compression ratios can be obtained with no visible compression 74artifacts, and extremely high compression ratios are possible if you are 75willing to sacrifice image quality (by reducing the "quality" setting in the 76compressor.) 77 78This software implements JPEG baseline, extended-sequential, and progressive 79compression processes. Provision is made for supporting all variants of these 80processes, although some uncommon parameter settings aren't implemented yet. 81We have made no provision for supporting the hierarchical or lossless 82processes defined in the standard. 83 84We provide a set of library routines for reading and writing JPEG image files, 85plus two sample applications "cjpeg" and "djpeg", which use the library to 86perform conversion between JPEG and some other popular image file formats. 87The library is intended to be reused in other applications. 88 89In order to support file conversion and viewing software, we have included 90considerable functionality beyond the bare JPEG coding/decoding capability; 91for example, the color quantization modules are not strictly part of JPEG 92decoding, but they are essential for output to colormapped file formats or 93colormapped displays. These extra functions can be compiled out of the 94library if not required for a particular application. 95 96We have also included "jpegtran", a utility for lossless transcoding between 97different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple 98applications for inserting and extracting textual comments in JFIF files. 99 100The emphasis in designing this software has been on achieving portability and 101flexibility, while also making it fast enough to be useful. In particular, 102the software is not intended to be read as a tutorial on JPEG. (See the 103REFERENCES section for introductory material.) Rather, it is intended to 104be reliable, portable, industrial-strength code. We do not claim to have 105achieved that goal in every aspect of the software, but we strive for it. 106 107We welcome the use of this software as a component of commercial products. 108No royalty is required, but we do ask for an acknowledgement in product 109documentation, as described under LEGAL ISSUES. 110 111 112LEGAL ISSUES 113============ 114 115In plain English: 116 1171. We don't promise that this software works. (But if you find any bugs, 118 please let us know!) 1192. You can use this software for whatever you want. You don't have to pay us. 1203. You may not pretend that you wrote this software. If you use it in a 121 program, you must acknowledge somewhere in your documentation that 122 you've used the IJG code. 123 124In legalese: 125 126The authors make NO WARRANTY or representation, either express or implied, 127with respect to this software, its quality, accuracy, merchantability, or 128fitness for a particular purpose. This software is provided "AS IS", and you, 129its user, assume the entire risk as to its quality and accuracy. 130 131This software is copyright (C) 1991-2012, Thomas G. Lane, Guido Vollbeding. 132All Rights Reserved except as specified below. 133 134Permission is hereby granted to use, copy, modify, and distribute this 135software (or portions thereof) for any purpose, without fee, subject to these 136conditions: 137(1) If any part of the source code for this software is distributed, then this 138README file must be included, with this copyright and no-warranty notice 139unaltered; and any additions, deletions, or changes to the original files 140must be clearly indicated in accompanying documentation. 141(2) If only executable code is distributed, then the accompanying 142documentation must state that "this software is based in part on the work of 143the Independent JPEG Group". 144(3) Permission for use of this software is granted only if the user accepts 145full responsibility for any undesirable consequences; the authors accept 146NO LIABILITY for damages of any kind. 147 148These conditions apply to any software derived from or based on the IJG code, 149not just to the unmodified library. If you use our work, you ought to 150acknowledge us. 151 152Permission is NOT granted for the use of any IJG author's name or company name 153in advertising or publicity relating to this software or products derived from 154it. This software may be referred to only as "the Independent JPEG Group's 155software". 156 157We specifically permit and encourage the use of this software as the basis of 158commercial products, provided that all warranty or liability claims are 159assumed by the product vendor. 160 161 162The Unix configuration script "configure" was produced with GNU Autoconf. 163It is copyright by the Free Software Foundation but is freely distributable. 164The same holds for its supporting scripts (config.guess, config.sub, 165ltmain.sh). Another support script, install-sh, is copyright by X Consortium 166but is also freely distributable. 167 168The IJG distribution formerly included code to read and write GIF files. 169To avoid entanglement with the Unisys LZW patent, GIF reading support has 170been removed altogether, and the GIF writer has been simplified to produce 171"uncompressed GIFs". This technique does not use the LZW algorithm; the 172resulting GIF files are larger than usual, but are readable by all standard 173GIF decoders. 174 175We are required to state that 176 "The Graphics Interchange Format(c) is the Copyright property of 177 CompuServe Incorporated. GIF(sm) is a Service Mark property of 178 CompuServe Incorporated." 179 180 181REFERENCES 182========== 183 184We recommend reading one or more of these references before trying to 185understand the innards of the JPEG software. 186 187The best short technical introduction to the JPEG compression algorithm is 188 Wallace, Gregory K. "The JPEG Still Picture Compression Standard", 189 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. 190(Adjacent articles in that issue discuss MPEG motion picture compression, 191applications of JPEG, and related topics.) If you don't have the CACM issue 192handy, a PostScript file containing a revised version of Wallace's article is 193available at http://www.ijg.org/files/wallace.ps.gz. The file (actually 194a preprint for an article that appeared in IEEE Trans. Consumer Electronics) 195omits the sample images that appeared in CACM, but it includes corrections 196and some added material. Note: the Wallace article is copyright ACM and IEEE, 197and it may not be used for commercial purposes. 198 199A somewhat less technical, more leisurely introduction to JPEG can be found in 200"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by 201M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides 202good explanations and example C code for a multitude of compression methods 203including JPEG. It is an excellent source if you are comfortable reading C 204code but don't know much about data compression in general. The book's JPEG 205sample code is far from industrial-strength, but when you are ready to look 206at a full implementation, you've got one here... 207 208The best currently available description of JPEG is the textbook "JPEG Still 209Image Data Compression Standard" by William B. Pennebaker and Joan L. 210Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. 211Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG 212standards (DIS 10918-1 and draft DIS 10918-2). 213 214The original JPEG standard is divided into two parts, Part 1 being the actual 215specification, while Part 2 covers compliance testing methods. Part 1 is 216titled "Digital Compression and Coding of Continuous-tone Still Images, 217Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS 21810918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of 219Continuous-tone Still Images, Part 2: Compliance testing" and has document 220numbers ISO/IEC IS 10918-2, ITU-T T.83. 221 222The JPEG standard does not specify all details of an interchangeable file 223format. For the omitted details we follow the "JFIF" conventions, revision 2241.02. JFIF 1.02 has been adopted as an Ecma International Technical Report 225and thus received a formal publication status. It is available as a free 226download in PDF format from 227http://www.ecma-international.org/publications/techreports/E-TR-098.htm. 228A PostScript version of the JFIF document is available at 229http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at 230http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures. 231 232The TIFF 6.0 file format specification can be obtained by FTP from 233ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme 234found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. 235IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). 236Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 237(Compression tag 7). Copies of this Note can be obtained from 238http://www.ijg.org/files/. It is expected that the next revision 239of the TIFF spec will replace the 6.0 JPEG design with the Note's design. 240Although IJG's own code does not support TIFF/JPEG, the free libtiff library 241uses our library to implement TIFF/JPEG per the Note. 242 243 244ARCHIVE LOCATIONS 245================= 246 247The "official" archive site for this software is www.ijg.org. 248The most recent released version can always be found there in 249directory "files". This particular version will be archived as 250http://www.ijg.org/files/jpegsrc.v8d.tar.gz, and in Windows-compatible 251"zip" archive format as http://www.ijg.org/files/jpegsr8d.zip. 252 253The JPEG FAQ (Frequently Asked Questions) article is a source of some 254general information about JPEG. 255It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ 256and other news.answers archive sites, including the official news.answers 257archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. 258If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu 259with body 260 send usenet/news.answers/jpeg-faq/part1 261 send usenet/news.answers/jpeg-faq/part2 262 263 264FILE FORMAT WARS 265================ 266 267The ISO/IEC JTC1/SC29/WG1 standards committee (also known as JPEG, together 268with ITU-T SG16) currently promotes different formats containing the name 269"JPEG" which are incompatible with original DCT-based JPEG. IJG therefore does 270not support these formats (see REFERENCES). Indeed, one of the original 271reasons for developing this free software was to help force convergence on 272common, interoperable format standards for JPEG files. 273Don't use an incompatible file format! 274(In any case, our decoder will remain capable of reading existing JPEG 275image files indefinitely.) 276 277 278TO DO 279===== 280 281Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org. 282