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 install.txt How to configure and install the IJG software. 40 usage.txt Usage instructions for cjpeg, djpeg, jpegtran, 41 rdjpgcom, and wrjpgcom. 42 *.1 Unix-style man pages for programs (same info as usage.txt). 43 wizard.txt Advanced usage instructions for JPEG wizards only. 44 change.log Version-to-version change highlights. 45Programmer and internal documentation: 46 libjpeg.txt How to use the JPEG library in your own programs. 47 example.c Sample code for calling the JPEG library. 48 structure.txt Overview of the JPEG library's internal structure. 49 coderules.txt Coding style rules --- please read if you contribute code. 50 51Please read at least the files install.txt and usage.txt. Some information 52can also be found in the JPEG FAQ (Frequently Asked Questions) article. See 53ARCHIVE LOCATIONS below to find out where to obtain the FAQ article. 54 55If you want to understand how the JPEG code works, we suggest reading one or 56more of the REFERENCES, then looking at the documentation files (in roughly 57the order listed) before diving into the code. 58 59 60OVERVIEW 61======== 62 63This package contains C software to implement JPEG image encoding, decoding, 64and transcoding. JPEG (pronounced "jay-peg") is a standardized compression 65method for full-color and gray-scale images. JPEG's strong suit is compressing 66photographic images or other types of images that have smooth color and 67brightness transitions between neighboring pixels. Images with sharp lines or 68other abrupt features may not compress well with JPEG, and a higher JPEG 69quality may have to be used to avoid visible compression artifacts with such 70images. 71 72JPEG is lossy, meaning that the output pixels are not necessarily identical to 73the input pixels. However, on photographic content and other "smooth" images, 74very good compression ratios can be obtained with no visible compression 75artifacts, and extremely high compression ratios are possible if you are 76willing to sacrifice image quality (by reducing the "quality" setting in the 77compressor.) 78 79This software implements JPEG baseline, extended-sequential, and progressive 80compression processes. Provision is made for supporting all variants of these 81processes, although some uncommon parameter settings aren't implemented yet. 82We have made no provision for supporting the hierarchical or lossless 83processes defined in the standard. 84 85We provide a set of library routines for reading and writing JPEG image files, 86plus two sample applications "cjpeg" and "djpeg", which use the library to 87perform conversion between JPEG and some other popular image file formats. 88The library is intended to be reused in other applications. 89 90In order to support file conversion and viewing software, we have included 91considerable functionality beyond the bare JPEG coding/decoding capability; 92for example, the color quantization modules are not strictly part of JPEG 93decoding, but they are essential for output to colormapped file formats or 94colormapped displays. These extra functions can be compiled out of the 95library if not required for a particular application. 96 97We have also included "jpegtran", a utility for lossless transcoding between 98different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple 99applications for inserting and extracting textual comments in JFIF files. 100 101The emphasis in designing this software has been on achieving portability and 102flexibility, while also making it fast enough to be useful. In particular, 103the software is not intended to be read as a tutorial on JPEG. (See the 104REFERENCES section for introductory material.) Rather, it is intended to 105be reliable, portable, industrial-strength code. We do not claim to have 106achieved that goal in every aspect of the software, but we strive for it. 107 108We welcome the use of this software as a component of commercial products. 109No royalty is required, but we do ask for an acknowledgement in product 110documentation, as described under LEGAL ISSUES. 111 112 113LEGAL ISSUES 114============ 115 116In plain English: 117 1181. We don't promise that this software works. (But if you find any bugs, 119 please let us know!) 1202. You can use this software for whatever you want. You don't have to pay us. 1213. You may not pretend that you wrote this software. If you use it in a 122 program, you must acknowledge somewhere in your documentation that 123 you've used the IJG code. 124 125In legalese: 126 127The authors make NO WARRANTY or representation, either express or implied, 128with respect to this software, its quality, accuracy, merchantability, or 129fitness for a particular purpose. This software is provided "AS IS", and you, 130its user, assume the entire risk as to its quality and accuracy. 131 132This software is copyright (C) 1991-2012, Thomas G. Lane, Guido Vollbeding. 133All Rights Reserved except as specified below. 134 135Permission is hereby granted to use, copy, modify, and distribute this 136software (or portions thereof) for any purpose, without fee, subject to these 137conditions: 138(1) If any part of the source code for this software is distributed, then this 139README file must be included, with this copyright and no-warranty notice 140unaltered; and any additions, deletions, or changes to the original files 141must be clearly indicated in accompanying documentation. 142(2) If only executable code is distributed, then the accompanying 143documentation must state that "this software is based in part on the work of 144the Independent JPEG Group". 145(3) Permission for use of this software is granted only if the user accepts 146full responsibility for any undesirable consequences; the authors accept 147NO LIABILITY for damages of any kind. 148 149These conditions apply to any software derived from or based on the IJG code, 150not just to the unmodified library. If you use our work, you ought to 151acknowledge us. 152 153Permission is NOT granted for the use of any IJG author's name or company name 154in advertising or publicity relating to this software or products derived from 155it. This software may be referred to only as "the Independent JPEG Group's 156software". 157 158We specifically permit and encourage the use of this software as the basis of 159commercial products, provided that all warranty or liability claims are 160assumed by the product vendor. 161 162 163The Unix configuration script "configure" was produced with GNU Autoconf. 164It is copyright by the Free Software Foundation but is freely distributable. 165The same holds for its supporting scripts (config.guess, config.sub, 166ltmain.sh). Another support script, install-sh, is copyright by X Consortium 167but is also freely distributable. 168 169The IJG distribution formerly included code to read and write GIF files. 170To avoid entanglement with the Unisys LZW patent, GIF reading support has 171been removed altogether, and the GIF writer has been simplified to produce 172"uncompressed GIFs". This technique does not use the LZW algorithm; the 173resulting GIF files are larger than usual, but are readable by all standard 174GIF decoders. 175 176We are required to state that 177 "The Graphics Interchange Format(c) is the Copyright property of 178 CompuServe Incorporated. GIF(sm) is a Service Mark property of 179 CompuServe Incorporated." 180 181 182REFERENCES 183========== 184 185We recommend reading one or more of these references before trying to 186understand the innards of the JPEG software. 187 188The best short technical introduction to the JPEG compression algorithm is 189 Wallace, Gregory K. "The JPEG Still Picture Compression Standard", 190 Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. 191(Adjacent articles in that issue discuss MPEG motion picture compression, 192applications of JPEG, and related topics.) If you don't have the CACM issue 193handy, a PostScript file containing a revised version of Wallace's article is 194available at http://www.ijg.org/files/wallace.ps.gz. The file (actually 195a preprint for an article that appeared in IEEE Trans. Consumer Electronics) 196omits the sample images that appeared in CACM, but it includes corrections 197and some added material. Note: the Wallace article is copyright ACM and IEEE, 198and it may not be used for commercial purposes. 199 200A somewhat less technical, more leisurely introduction to JPEG can be found in 201"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by 202M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides 203good explanations and example C code for a multitude of compression methods 204including JPEG. It is an excellent source if you are comfortable reading C 205code but don't know much about data compression in general. The book's JPEG 206sample code is far from industrial-strength, but when you are ready to look 207at a full implementation, you've got one here... 208 209The best currently available description of JPEG is the textbook "JPEG Still 210Image Data Compression Standard" by William B. Pennebaker and Joan L. 211Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. 212Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG 213standards (DIS 10918-1 and draft DIS 10918-2). 214 215The original JPEG standard is divided into two parts, Part 1 being the actual 216specification, while Part 2 covers compliance testing methods. Part 1 is 217titled "Digital Compression and Coding of Continuous-tone Still Images, 218Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS 21910918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of 220Continuous-tone Still Images, Part 2: Compliance testing" and has document 221numbers ISO/IEC IS 10918-2, ITU-T T.83. 222 223The JPEG standard does not specify all details of an interchangeable file 224format. For the omitted details we follow the "JFIF" conventions, revision 2251.02. JFIF 1.02 has been adopted as an Ecma International Technical Report 226and thus received a formal publication status. It is available as a free 227download in PDF format from 228http://www.ecma-international.org/publications/techreports/E-TR-098.htm. 229A PostScript version of the JFIF document is available at 230http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at 231http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures. 232 233The TIFF 6.0 file format specification can be obtained by FTP from 234ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme 235found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. 236IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). 237Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 238(Compression tag 7). Copies of this Note can be obtained from 239http://www.ijg.org/files/. It is expected that the next revision 240of the TIFF spec will replace the 6.0 JPEG design with the Note's design. 241Although IJG's own code does not support TIFF/JPEG, the free libtiff library 242uses our library to implement TIFF/JPEG per the Note. 243 244 245ARCHIVE LOCATIONS 246================= 247 248The "official" archive site for this software is www.ijg.org. 249The most recent released version can always be found there in 250directory "files". This particular version will be archived as 251http://www.ijg.org/files/jpegsrc.v8d.tar.gz, and in Windows-compatible 252"zip" archive format as http://www.ijg.org/files/jpegsr8d.zip. 253 254The JPEG FAQ (Frequently Asked Questions) article is a source of some 255general information about JPEG. 256It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ 257and other news.answers archive sites, including the official news.answers 258archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. 259If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu 260with body 261 send usenet/news.answers/jpeg-faq/part1 262 send usenet/news.answers/jpeg-faq/part2 263 264 265FILE FORMAT WARS 266================ 267 268The ISO/IEC JTC1/SC29/WG1 standards committee (also known as JPEG, together 269with ITU-T SG16) currently promotes different formats containing the name 270"JPEG" which are incompatible with original DCT-based JPEG. IJG therefore does 271not support these formats (see REFERENCES). Indeed, one of the original 272reasons for developing this free software was to help force convergence on 273common, interoperable format standards for JPEG files. 274Don't use an incompatible file format! 275(In any case, our decoder will remain capable of reading existing JPEG 276image files indefinitely.) 277 278 279TO DO 280===== 281 282Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org. 283