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1.4 +libjpeg-turbo note: This file has been modified by The libjpeg-turbo Project
1.5 +to include only information relevant to libjpeg-turbo, to wordsmith certain
1.6 +sections, and to remove impolitic language that existed in the libjpeg v8
1.7 +README. It is included only for reference. Please see README-turbo.txt for
1.8 +information specific to libjpeg-turbo.
1.9 +
1.10 +
1.11 +The Independent JPEG Group's JPEG software
1.12 +==========================================
1.13 +
1.14 +This distribution contains a release of the Independent JPEG Group's free JPEG
1.15 +software. You are welcome to redistribute this software and to use it for any
1.16 +purpose, subject to the conditions under LEGAL ISSUES, below.
1.17 +
1.18 +This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone,
1.19 +Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson,
1.20 +Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers,
1.21 +and other members of the Independent JPEG Group.
1.22 +
1.23 +IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee
1.24 +(also known as JPEG, together with ITU-T SG16).
1.25 +
1.26 +
1.27 +DOCUMENTATION ROADMAP
1.28 +=====================
1.29 +
1.30 +This file contains the following sections:
1.31 +
1.32 +OVERVIEW General description of JPEG and the IJG software.
1.33 +LEGAL ISSUES Copyright, lack of warranty, terms of distribution.
1.34 +REFERENCES Where to learn more about JPEG.
1.35 +ARCHIVE LOCATIONS Where to find newer versions of this software.
1.36 +FILE FORMAT WARS Software *not* to get.
1.37 +TO DO Plans for future IJG releases.
1.38 +
1.39 +Other documentation files in the distribution are:
1.40 +
1.41 +User documentation:
1.42 + install.txt How to configure and install the IJG software.
1.43 + usage.txt Usage instructions for cjpeg, djpeg, jpegtran,
1.44 + rdjpgcom, and wrjpgcom.
1.45 + *.1 Unix-style man pages for programs (same info as usage.txt).
1.46 + wizard.txt Advanced usage instructions for JPEG wizards only.
1.47 + change.log Version-to-version change highlights.
1.48 +Programmer and internal documentation:
1.49 + libjpeg.txt How to use the JPEG library in your own programs.
1.50 + example.c Sample code for calling the JPEG library.
1.51 + structure.txt Overview of the JPEG library's internal structure.
1.52 + coderules.txt Coding style rules --- please read if you contribute code.
1.53 +
1.54 +Please read at least the files install.txt and usage.txt. Some information
1.55 +can also be found in the JPEG FAQ (Frequently Asked Questions) article. See
1.56 +ARCHIVE LOCATIONS below to find out where to obtain the FAQ article.
1.57 +
1.58 +If you want to understand how the JPEG code works, we suggest reading one or
1.59 +more of the REFERENCES, then looking at the documentation files (in roughly
1.60 +the order listed) before diving into the code.
1.61 +
1.62 +
1.63 +OVERVIEW
1.64 +========
1.65 +
1.66 +This package contains C software to implement JPEG image encoding, decoding,
1.67 +and transcoding. JPEG (pronounced "jay-peg") is a standardized compression
1.68 +method for full-color and gray-scale images. JPEG's strong suit is compressing
1.69 +photographic images or other types of images that have smooth color and
1.70 +brightness transitions between neighboring pixels. Images with sharp lines or
1.71 +other abrupt features may not compress well with JPEG, and a higher JPEG
1.72 +quality may have to be used to avoid visible compression artifacts with such
1.73 +images.
1.74 +
1.75 +JPEG is lossy, meaning that the output pixels are not necessarily identical to
1.76 +the input pixels. However, on photographic content and other "smooth" images,
1.77 +very good compression ratios can be obtained with no visible compression
1.78 +artifacts, and extremely high compression ratios are possible if you are
1.79 +willing to sacrifice image quality (by reducing the "quality" setting in the
1.80 +compressor.)
1.81 +
1.82 +This software implements JPEG baseline, extended-sequential, and progressive
1.83 +compression processes. Provision is made for supporting all variants of these
1.84 +processes, although some uncommon parameter settings aren't implemented yet.
1.85 +We have made no provision for supporting the hierarchical or lossless
1.86 +processes defined in the standard.
1.87 +
1.88 +We provide a set of library routines for reading and writing JPEG image files,
1.89 +plus two sample applications "cjpeg" and "djpeg", which use the library to
1.90 +perform conversion between JPEG and some other popular image file formats.
1.91 +The library is intended to be reused in other applications.
1.92 +
1.93 +In order to support file conversion and viewing software, we have included
1.94 +considerable functionality beyond the bare JPEG coding/decoding capability;
1.95 +for example, the color quantization modules are not strictly part of JPEG
1.96 +decoding, but they are essential for output to colormapped file formats or
1.97 +colormapped displays. These extra functions can be compiled out of the
1.98 +library if not required for a particular application.
1.99 +
1.100 +We have also included "jpegtran", a utility for lossless transcoding between
1.101 +different JPEG processes, and "rdjpgcom" and "wrjpgcom", two simple
1.102 +applications for inserting and extracting textual comments in JFIF files.
1.103 +
1.104 +The emphasis in designing this software has been on achieving portability and
1.105 +flexibility, while also making it fast enough to be useful. In particular,
1.106 +the software is not intended to be read as a tutorial on JPEG. (See the
1.107 +REFERENCES section for introductory material.) Rather, it is intended to
1.108 +be reliable, portable, industrial-strength code. We do not claim to have
1.109 +achieved that goal in every aspect of the software, but we strive for it.
1.110 +
1.111 +We welcome the use of this software as a component of commercial products.
1.112 +No royalty is required, but we do ask for an acknowledgement in product
1.113 +documentation, as described under LEGAL ISSUES.
1.114 +
1.115 +
1.116 +LEGAL ISSUES
1.117 +============
1.118 +
1.119 +In plain English:
1.120 +
1.121 +1. We don't promise that this software works. (But if you find any bugs,
1.122 + please let us know!)
1.123 +2. You can use this software for whatever you want. You don't have to pay us.
1.124 +3. You may not pretend that you wrote this software. If you use it in a
1.125 + program, you must acknowledge somewhere in your documentation that
1.126 + you've used the IJG code.
1.127 +
1.128 +In legalese:
1.129 +
1.130 +The authors make NO WARRANTY or representation, either express or implied,
1.131 +with respect to this software, its quality, accuracy, merchantability, or
1.132 +fitness for a particular purpose. This software is provided "AS IS", and you,
1.133 +its user, assume the entire risk as to its quality and accuracy.
1.134 +
1.135 +This software is copyright (C) 1991-2012, Thomas G. Lane, Guido Vollbeding.
1.136 +All Rights Reserved except as specified below.
1.137 +
1.138 +Permission is hereby granted to use, copy, modify, and distribute this
1.139 +software (or portions thereof) for any purpose, without fee, subject to these
1.140 +conditions:
1.141 +(1) If any part of the source code for this software is distributed, then this
1.142 +README file must be included, with this copyright and no-warranty notice
1.143 +unaltered; and any additions, deletions, or changes to the original files
1.144 +must be clearly indicated in accompanying documentation.
1.145 +(2) If only executable code is distributed, then the accompanying
1.146 +documentation must state that "this software is based in part on the work of
1.147 +the Independent JPEG Group".
1.148 +(3) Permission for use of this software is granted only if the user accepts
1.149 +full responsibility for any undesirable consequences; the authors accept
1.150 +NO LIABILITY for damages of any kind.
1.151 +
1.152 +These conditions apply to any software derived from or based on the IJG code,
1.153 +not just to the unmodified library. If you use our work, you ought to
1.154 +acknowledge us.
1.155 +
1.156 +Permission is NOT granted for the use of any IJG author's name or company name
1.157 +in advertising or publicity relating to this software or products derived from
1.158 +it. This software may be referred to only as "the Independent JPEG Group's
1.159 +software".
1.160 +
1.161 +We specifically permit and encourage the use of this software as the basis of
1.162 +commercial products, provided that all warranty or liability claims are
1.163 +assumed by the product vendor.
1.164 +
1.165 +
1.166 +The Unix configuration script "configure" was produced with GNU Autoconf.
1.167 +It is copyright by the Free Software Foundation but is freely distributable.
1.168 +The same holds for its supporting scripts (config.guess, config.sub,
1.169 +ltmain.sh). Another support script, install-sh, is copyright by X Consortium
1.170 +but is also freely distributable.
1.171 +
1.172 +The IJG distribution formerly included code to read and write GIF files.
1.173 +To avoid entanglement with the Unisys LZW patent, GIF reading support has
1.174 +been removed altogether, and the GIF writer has been simplified to produce
1.175 +"uncompressed GIFs". This technique does not use the LZW algorithm; the
1.176 +resulting GIF files are larger than usual, but are readable by all standard
1.177 +GIF decoders.
1.178 +
1.179 +We are required to state that
1.180 + "The Graphics Interchange Format(c) is the Copyright property of
1.181 + CompuServe Incorporated. GIF(sm) is a Service Mark property of
1.182 + CompuServe Incorporated."
1.183 +
1.184 +
1.185 +REFERENCES
1.186 +==========
1.187 +
1.188 +We recommend reading one or more of these references before trying to
1.189 +understand the innards of the JPEG software.
1.190 +
1.191 +The best short technical introduction to the JPEG compression algorithm is
1.192 + Wallace, Gregory K. "The JPEG Still Picture Compression Standard",
1.193 + Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44.
1.194 +(Adjacent articles in that issue discuss MPEG motion picture compression,
1.195 +applications of JPEG, and related topics.) If you don't have the CACM issue
1.196 +handy, a PostScript file containing a revised version of Wallace's article is
1.197 +available at http://www.ijg.org/files/wallace.ps.gz. The file (actually
1.198 +a preprint for an article that appeared in IEEE Trans. Consumer Electronics)
1.199 +omits the sample images that appeared in CACM, but it includes corrections
1.200 +and some added material. Note: the Wallace article is copyright ACM and IEEE,
1.201 +and it may not be used for commercial purposes.
1.202 +
1.203 +A somewhat less technical, more leisurely introduction to JPEG can be found in
1.204 +"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by
1.205 +M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides
1.206 +good explanations and example C code for a multitude of compression methods
1.207 +including JPEG. It is an excellent source if you are comfortable reading C
1.208 +code but don't know much about data compression in general. The book's JPEG
1.209 +sample code is far from industrial-strength, but when you are ready to look
1.210 +at a full implementation, you've got one here...
1.211 +
1.212 +The best currently available description of JPEG is the textbook "JPEG Still
1.213 +Image Data Compression Standard" by William B. Pennebaker and Joan L.
1.214 +Mitchell, published by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1.
1.215 +Price US$59.95, 638 pp. The book includes the complete text of the ISO JPEG
1.216 +standards (DIS 10918-1 and draft DIS 10918-2).
1.217 +
1.218 +The original JPEG standard is divided into two parts, Part 1 being the actual
1.219 +specification, while Part 2 covers compliance testing methods. Part 1 is
1.220 +titled "Digital Compression and Coding of Continuous-tone Still Images,
1.221 +Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS
1.222 +10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of
1.223 +Continuous-tone Still Images, Part 2: Compliance testing" and has document
1.224 +numbers ISO/IEC IS 10918-2, ITU-T T.83.
1.225 +
1.226 +The JPEG standard does not specify all details of an interchangeable file
1.227 +format. For the omitted details we follow the "JFIF" conventions, revision
1.228 +1.02. JFIF 1.02 has been adopted as an Ecma International Technical Report
1.229 +and thus received a formal publication status. It is available as a free
1.230 +download in PDF format from
1.231 +http://www.ecma-international.org/publications/techreports/E-TR-098.htm.
1.232 +A PostScript version of the JFIF document is available at
1.233 +http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at
1.234 +http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures.
1.235 +
1.236 +The TIFF 6.0 file format specification can be obtained by FTP from
1.237 +ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme
1.238 +found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems.
1.239 +IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6).
1.240 +Instead, we recommend the JPEG design proposed by TIFF Technical Note #2
1.241 +(Compression tag 7). Copies of this Note can be obtained from
1.242 +http://www.ijg.org/files/. It is expected that the next revision
1.243 +of the TIFF spec will replace the 6.0 JPEG design with the Note's design.
1.244 +Although IJG's own code does not support TIFF/JPEG, the free libtiff library
1.245 +uses our library to implement TIFF/JPEG per the Note.
1.246 +
1.247 +
1.248 +ARCHIVE LOCATIONS
1.249 +=================
1.250 +
1.251 +The "official" archive site for this software is www.ijg.org.
1.252 +The most recent released version can always be found there in
1.253 +directory "files". This particular version will be archived as
1.254 +http://www.ijg.org/files/jpegsrc.v8d.tar.gz, and in Windows-compatible
1.255 +"zip" archive format as http://www.ijg.org/files/jpegsr8d.zip.
1.256 +
1.257 +The JPEG FAQ (Frequently Asked Questions) article is a source of some
1.258 +general information about JPEG.
1.259 +It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/
1.260 +and other news.answers archive sites, including the official news.answers
1.261 +archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/.
1.262 +If you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu
1.263 +with body
1.264 + send usenet/news.answers/jpeg-faq/part1
1.265 + send usenet/news.answers/jpeg-faq/part2
1.266 +
1.267 +
1.268 +FILE FORMAT WARS
1.269 +================
1.270 +
1.271 +The ISO/IEC JTC1/SC29/WG1 standards committee (also known as JPEG, together
1.272 +with ITU-T SG16) currently promotes different formats containing the name
1.273 +"JPEG" which are incompatible with original DCT-based JPEG. IJG therefore does
1.274 +not support these formats (see REFERENCES). Indeed, one of the original
1.275 +reasons for developing this free software was to help force convergence on
1.276 +common, interoperable format standards for JPEG files.
1.277 +Don't use an incompatible file format!
1.278 +(In any case, our decoder will remain capable of reading existing JPEG
1.279 +image files indefinitely.)
1.280 +
1.281 +
1.282 +TO DO
1.283 +=====
1.284 +
1.285 +Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org.
