1 libjpeg-turbo note: This file has been modified by The libjpeg-turbo Project 2 to include only information relevant to libjpeg-turbo, to wordsmith certain 3 sections, and to remove impolitic language that existed in the libjpeg v8 4 README. It is included only for reference. Please see README-turbo.txt for 5 information specific to libjpeg-turbo. 6 7 8 The Independent JPEG Group's JPEG software 9 ========================================== 10 11 This distribution contains a release of the Independent JPEG Group's free JPEG 12 software. You are welcome to redistribute this software and to use it for any 13 purpose, subject to the conditions under LEGAL ISSUES, below. 14 15 This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone, 16 Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson, 17 Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers, 18 and other members of the Independent JPEG Group. 19 20 IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee 21 (also known as JPEG, together with ITU-T SG16). 22 23 24 DOCUMENTATION ROADMAP 25 ===================== 26 27 This file contains the following sections: 28 29 OVERVIEW General description of JPEG and the IJG software. 30 LEGAL ISSUES Copyright, lack of warranty, terms of distribution. 31 REFERENCES Where to learn more about JPEG. 32 ARCHIVE LOCATIONS Where to find newer versions of this software. 33 FILE FORMAT WARS Software *not* to get. 34 TO DO Plans for future IJG releases. 35 36 Other documentation files in the distribution are: 37 38 User 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. 45 Programmer 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 51 Please read at least the files install.txt and usage.txt. Some information 52 can also be found in the JPEG FAQ (Frequently Asked Questions) article. See 53 ARCHIVE LOCATIONS below to find out where to obtain the FAQ article. 54 55 If you want to understand how the JPEG code works, we suggest reading one or 56 more of the REFERENCES, then looking at the documentation files (in roughly 57 the order listed) before diving into the code. 58 59 60 OVERVIEW 61 ======== 62 63 This package contains C software to implement JPEG image encoding, decoding, 64 and transcoding. JPEG (pronounced "jay-peg") is a standardized compression 65 method for full-color and gray-scale images. JPEG's strong suit is compressing 66 photographic images or other types of images that have smooth color and 67 brightness transitions between neighboring pixels. Images with sharp lines or 68 other abrupt features may not compress well with JPEG, and a higher JPEG 69 quality may have to be used to avoid visible compression artifacts with such 70 images. 71 72 JPEG is lossy, meaning that the output pixels are not necessarily identical to 73 the input pixels. However, on photographic content and other "smooth" images, 74 very good compression ratios can be obtained with no visible compression 75 artifacts, and extremely high compression ratios are possible if you are 76 willing to sacrifice image quality (by reducing the "quality" setting in the 77 compressor.) 78 79 This software implements JPEG baseline, extended-sequential, and progressive 80 compression processes. Provision is made for supporting all variants of these 81 processes, although some uncommon parameter settings aren't implemented yet. 82 We have made no provision for supporting the hierarchical or lossless 83 processes defined in the standard. 84 85 We provide a set of library routines for reading and writing JPEG image files, 86 plus two sample applications "cjpeg" and "djpeg", which use the library to 87 perform conversion between JPEG and some other popular image file formats. 88 The library is intended to be reused in other applications. 89 90 In order to support file conversion and viewing software, we have included 91 considerable functionality beyond the bare JPEG coding/decoding capability; 92 for example, the color quantization modules are not strictly part of JPEG 93 decoding, but they are essential for output to colormapped file formats or 94 colormapped displays. These extra functions can be compiled out of the 95 library if not required for a particular application. 96 97 We have also included "jpegtran", a utility for lossless transcoding between 98 different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple 99 applications for inserting and extracting textual comments in JFIF files. 100 101 The emphasis in designing this software has been on achieving portability and 102 flexibility, while also making it fast enough to be useful. In particular, 103 the software is not intended to be read as a tutorial on JPEG. (See the 104 REFERENCES section for introductory material.) Rather, it is intended to 105 be reliable, portable, industrial-strength code. We do not claim to have 106 achieved that goal in every aspect of the software, but we strive for it. 107 108 We welcome the use of this software as a component of commercial products. 109 No royalty is required, but we do ask for an acknowledgement in product 110 documentation, as described under LEGAL ISSUES. 111 112 113 LEGAL ISSUES 114 ============ 115 116 In plain English: 117 118 1. We don't promise that this software works. (But if you find any bugs, 119 please let us know!) 120 2. You can use this software for whatever you want. You don't have to pay us. 121 3. 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. 124 125 In legalese: 126 127 The authors make NO WARRANTY or representation, either express or implied, 128 with respect to this software, its quality, accuracy, merchantability, or 129 fitness for a particular purpose. This software is provided "AS IS", and you, 130 its user, assume the entire risk as to its quality and accuracy. 131 132 This software is copyright (C) 1991-2012, Thomas G. Lane, Guido Vollbeding. 133 All Rights Reserved except as specified below. 134 135 Permission is hereby granted to use, copy, modify, and distribute this 136 software (or portions thereof) for any purpose, without fee, subject to these 137 conditions: 138 (1) If any part of the source code for this software is distributed, then this 139 README file must be included, with this copyright and no-warranty notice 140 unaltered; and any additions, deletions, or changes to the original files 141 must be clearly indicated in accompanying documentation. 142 (2) If only executable code is distributed, then the accompanying 143 documentation must state that "this software is based in part on the work of 144 the Independent JPEG Group". 145 (3) Permission for use of this software is granted only if the user accepts 146 full responsibility for any undesirable consequences; the authors accept 147 NO LIABILITY for damages of any kind. 148 149 These conditions apply to any software derived from or based on the IJG code, 150 not just to the unmodified library. If you use our work, you ought to 151 acknowledge us. 152 153 Permission is NOT granted for the use of any IJG author's name or company name 154 in advertising or publicity relating to this software or products derived from 155 it. This software may be referred to only as "the Independent JPEG Group's 156 software". 157 158 We specifically permit and encourage the use of this software as the basis of 159 commercial products, provided that all warranty or liability claims are 160 assumed by the product vendor. 161 162 163 The Unix configuration script "configure" was produced with GNU Autoconf. 164 It is copyright by the Free Software Foundation but is freely distributable. 165 The same holds for its supporting scripts (config.guess, config.sub, 166 ltmain.sh). Another support script, install-sh, is copyright by X Consortium 167 but is also freely distributable. 168 169 The IJG distribution formerly included code to read and write GIF files. 170 To avoid entanglement with the Unisys LZW patent, GIF reading support has 171 been removed altogether, and the GIF writer has been simplified to produce 172 "uncompressed GIFs". This technique does not use the LZW algorithm; the 173 resulting GIF files are larger than usual, but are readable by all standard 174 GIF decoders. 175 176 We 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." 180 181 182 REFERENCES 183 ========== 184 185 We recommend reading one or more of these references before trying to 186 understand the innards of the JPEG software. 187 188 The 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, 192 applications of JPEG, and related topics.) If you don't have the CACM issue 193 handy, a PostScript file containing a revised version of Wallace's article is 194 available at http://www.ijg.org/files/wallace.ps.gz. The file (actually 195 a preprint for an article that appeared in IEEE Trans. Consumer Electronics) 196 omits the sample images that appeared in CACM, but it includes corrections 197 and some added material. Note: the Wallace article is copyright ACM and IEEE, 198 and it may not be used for commercial purposes. 199 200 A 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 202 M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides 203 good explanations and example C code for a multitude of compression methods 204 including JPEG. It is an excellent source if you are comfortable reading C 205 code but don't know much about data compression in general. The book's JPEG 206 sample code is far from industrial-strength, but when you are ready to look 207 at a full implementation, you've got one here... 208 209 The best currently available description of JPEG is the textbook "JPEG Still 210 Image Data Compression Standard" by William B. Pennebaker and Joan L. 211 Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. 212 Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG 213 standards (DIS 10918-1 and draft DIS 10918-2). 214 215 The original JPEG standard is divided into two parts, Part 1 being the actual 216 specification, while Part 2 covers compliance testing methods. Part 1 is 217 titled "Digital Compression and Coding of Continuous-tone Still Images, 218 Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS 219 10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of 220 Continuous-tone Still Images, Part 2: Compliance testing" and has document 221 numbers ISO/IEC IS 10918-2, ITU-T T.83. 222 223 The JPEG standard does not specify all details of an interchangeable file 224 format. For the omitted details we follow the "JFIF" conventions, revision 225 1.02. JFIF 1.02 has been adopted as an Ecma International Technical Report 226 and thus received a formal publication status. It is available as a free 227 download in PDF format from 228 http://www.ecma-international.org/publications/techreports/E-TR-098.htm. 229 A PostScript version of the JFIF document is available at 230 http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at 231 http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures. 232 233 The TIFF 6.0 file format specification can be obtained by FTP from 234 ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme 235 found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. 236 IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). 237 Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 238 (Compression tag 7). Copies of this Note can be obtained from 239 http://www.ijg.org/files/. It is expected that the next revision 240 of the TIFF spec will replace the 6.0 JPEG design with the Note's design. 241 Although IJG's own code does not support TIFF/JPEG, the free libtiff library 242 uses our library to implement TIFF/JPEG per the Note. 243 244 245 ARCHIVE LOCATIONS 246 ================= 247 248 The "official" archive site for this software is www.ijg.org. 249 The most recent released version can always be found there in 250 directory "files". This particular version will be archived as 251 http://www.ijg.org/files/jpegsrc.v8d.tar.gz, and in Windows-compatible 252 "zip" archive format as http://www.ijg.org/files/jpegsr8d.zip. 253 254 The JPEG FAQ (Frequently Asked Questions) article is a source of some 255 general information about JPEG. 256 It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ 257 and other news.answers archive sites, including the official news.answers 258 archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. 259 If you don't have Web or FTP access, send e-mail to mail-server (a] rtfm.mit.edu 260 with body 261 send usenet/news.answers/jpeg-faq/part1 262 send usenet/news.answers/jpeg-faq/part2 263 264 265 FILE FORMAT WARS 266 ================ 267 268 The ISO/IEC JTC1/SC29/WG1 standards committee (also known as JPEG, together 269 with ITU-T SG16) currently promotes different formats containing the name 270 "JPEG" which are incompatible with original DCT-based JPEG. IJG therefore does 271 not support these formats (see REFERENCES). Indeed, one of the original 272 reasons for developing this free software was to help force convergence on 273 common, interoperable format standards for JPEG files. 274 Don't use an incompatible file format! 275 (In any case, our decoder will remain capable of reading existing JPEG 276 image files indefinitely.) 277 278 279 TO DO 280 ===== 281 282 Please send bug reports, offers of help, etc. to jpeg-info (a] jpegclub.org. 283
