1402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe Independent JPEG Group's JPEG software 2402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll========================================== 3402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 4402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollREADME for release 6b of 27-Mar-1998 5402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll==================================== 6402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 7402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThis distribution contains the sixth public release of the Independent JPEG 8402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollGroup's free JPEG software. You are welcome to redistribute this software and 9402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollto use it for any purpose, subject to the conditions under LEGAL ISSUES, below. 10402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 11402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollSerious users of this software (particularly those incorporating it into 12402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molllarger programs) should contact IJG at jpeg-info@uunet.uu.net to be added to 13402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollour electronic mailing list. Mailing list members are notified of updates 14402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molland have a chance to participate in technical discussions, etc. 15402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 16402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThis software is the work of Tom Lane, Philip Gladstone, Jim Boucher, 17402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollLee Crocker, Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, 18402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollGuido Vollbeding, Ge' Weijers, and other members of the Independent JPEG 19402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollGroup. 20402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 21402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIJG is not affiliated with the official ISO JPEG standards committee. 22402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 23402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 24402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollDOCUMENTATION ROADMAP 25402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll===================== 26402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 27402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThis file contains the following sections: 28402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 29402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollOVERVIEW General description of JPEG and the IJG software. 30402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollLEGAL ISSUES Copyright, lack of warranty, terms of distribution. 31402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollREFERENCES Where to learn more about JPEG. 32402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollARCHIVE LOCATIONS Where to find newer versions of this software. 33402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollRELATED SOFTWARE Other stuff you should get. 34402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollFILE FORMAT WARS Software *not* to get. 35402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollTO DO Plans for future IJG releases. 36402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 37402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollOther documentation files in the distribution are: 38402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 39402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollUser documentation: 40402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll install.doc How to configure and install the IJG software. 41402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll usage.doc Usage instructions for cjpeg, djpeg, jpegtran, 42402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll rdjpgcom, and wrjpgcom. 43402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll *.1 Unix-style man pages for programs (same info as usage.doc). 44402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll wizard.doc Advanced usage instructions for JPEG wizards only. 45402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll change.log Version-to-version change highlights. 46402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollProgrammer and internal documentation: 47402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll libjpeg.doc How to use the JPEG library in your own programs. 48402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll example.c Sample code for calling the JPEG library. 49402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll structure.doc Overview of the JPEG library's internal structure. 50402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll filelist.doc Road map of IJG files. 51402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll coderules.doc Coding style rules --- please read if you contribute code. 52402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 53402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollPlease read at least the files install.doc and usage.doc. Useful information 54402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollcan also be found in the JPEG FAQ (Frequently Asked Questions) article. See 55402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollARCHIVE LOCATIONS below to find out where to obtain the FAQ article. 56402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 57402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIf you want to understand how the JPEG code works, we suggest reading one or 58402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollmore of the REFERENCES, then looking at the documentation files (in roughly 59402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollthe order listed) before diving into the code. 60402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 61402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 62402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollOVERVIEW 63402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll======== 64402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 65402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThis package contains C software to implement JPEG image compression and 66402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molldecompression. JPEG (pronounced "jay-peg") is a standardized compression 67402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollmethod for full-color and gray-scale images. JPEG is intended for compressing 68402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll"real-world" scenes; line drawings, cartoons and other non-realistic images 69402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollare not its strong suit. JPEG is lossy, meaning that the output image is not 70402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollexactly identical to the input image. Hence you must not use JPEG if you 71402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollhave to have identical output bits. However, on typical photographic images, 72402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollvery good compression levels can be obtained with no visible change, and 73402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollremarkably high compression levels are possible if you can tolerate a 74402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molllow-quality image. For more details, see the references, or just experiment 75402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollwith various compression settings. 76402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 77402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThis software implements JPEG baseline, extended-sequential, and progressive 78402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollcompression processes. Provision is made for supporting all variants of these 79402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollprocesses, although some uncommon parameter settings aren't implemented yet. 80402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollFor legal reasons, we are not distributing code for the arithmetic-coding 81402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollvariants of JPEG; see LEGAL ISSUES. We have made no provision for supporting 82402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollthe hierarchical or lossless processes defined in the standard. 83402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 84402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollWe provide a set of library routines for reading and writing JPEG image files, 85402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollplus two sample applications "cjpeg" and "djpeg", which use the library to 86402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollperform conversion between JPEG and some other popular image file formats. 87402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe library is intended to be reused in other applications. 88402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 89402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIn order to support file conversion and viewing software, we have included 90402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollconsiderable functionality beyond the bare JPEG coding/decoding capability; 91402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollfor example, the color quantization modules are not strictly part of JPEG 92402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molldecoding, but they are essential for output to colormapped file formats or 93402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollcolormapped displays. These extra functions can be compiled out of the 94402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molllibrary if not required for a particular application. We have also included 95402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll"jpegtran", a utility for lossless transcoding between different JPEG 96402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollprocesses, and "rdjpgcom" and "wrjpgcom", two simple applications for 97402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollinserting and extracting textual comments in JFIF files. 98402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 99402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe emphasis in designing this software has been on achieving portability and 100402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollflexibility, while also making it fast enough to be useful. In particular, 101402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollthe software is not intended to be read as a tutorial on JPEG. (See the 102402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollREFERENCES section for introductory material.) Rather, it is intended to 103402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollbe reliable, portable, industrial-strength code. We do not claim to have 104402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollachieved that goal in every aspect of the software, but we strive for it. 105402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 106402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollWe welcome the use of this software as a component of commercial products. 107402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollNo royalty is required, but we do ask for an acknowledgement in product 108402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molldocumentation, as described under LEGAL ISSUES. 109402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 110402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 111402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollLEGAL ISSUES 112402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll============ 113402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 114402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIn plain English: 115402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 116402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll1. We don't promise that this software works. (But if you find any bugs, 117402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll please let us know!) 118402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll2. You can use this software for whatever you want. You don't have to pay us. 119402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll3. You may not pretend that you wrote this software. If you use it in a 120402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll program, you must acknowledge somewhere in your documentation that 121402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll you've used the IJG code. 122402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 123402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIn legalese: 124402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 125402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe authors make NO WARRANTY or representation, either express or implied, 126402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollwith respect to this software, its quality, accuracy, merchantability, or 127402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollfitness for a particular purpose. This software is provided "AS IS", and you, 128402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollits user, assume the entire risk as to its quality and accuracy. 129402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 130402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThis software is copyright (C) 1991-1998, Thomas G. Lane. 131402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollAll Rights Reserved except as specified below. 132402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 133402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollPermission is hereby granted to use, copy, modify, and distribute this 134402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollsoftware (or portions thereof) for any purpose, without fee, subject to these 135402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollconditions: 136402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll(1) If any part of the source code for this software is distributed, then this 137402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollREADME file must be included, with this copyright and no-warranty notice 138402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollunaltered; and any additions, deletions, or changes to the original files 139402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollmust be clearly indicated in accompanying documentation. 140402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll(2) If only executable code is distributed, then the accompanying 141402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molldocumentation must state that "this software is based in part on the work of 142402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollthe Independent JPEG Group". 143402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll(3) Permission for use of this software is granted only if the user accepts 144402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollfull responsibility for any undesirable consequences; the authors accept 145402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollNO LIABILITY for damages of any kind. 146402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 147402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThese conditions apply to any software derived from or based on the IJG code, 148402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollnot just to the unmodified library. If you use our work, you ought to 149402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollacknowledge us. 150402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 151402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollPermission is NOT granted for the use of any IJG author's name or company name 152402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollin advertising or publicity relating to this software or products derived from 153402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollit. This software may be referred to only as "the Independent JPEG Group's 154402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollsoftware". 155402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 156402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollWe specifically permit and encourage the use of this software as the basis of 157402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollcommercial products, provided that all warranty or liability claims are 158402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollassumed by the product vendor. 159402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 160402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 161402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollansi2knr.c is included in this distribution by permission of L. Peter Deutsch, 162402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollsole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA. 163402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollansi2knr.c is NOT covered by the above copyright and conditions, but instead 164402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollby the usual distribution terms of the Free Software Foundation; principally, 165402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollthat you must include source code if you redistribute it. (See the file 166402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollansi2knr.c for full details.) However, since ansi2knr.c is not needed as part 167402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollof any program generated from the IJG code, this does not limit you more than 168402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollthe foregoing paragraphs do. 169402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 170402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe Unix configuration script "configure" was produced with GNU Autoconf. 171402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIt is copyright by the Free Software Foundation but is freely distributable. 172402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe same holds for its supporting scripts (config.guess, config.sub, 173402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollltconfig, ltmain.sh). Another support script, install-sh, is copyright 174402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollby M.I.T. but is also freely distributable. 175402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 176402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIt appears that the arithmetic coding option of the JPEG spec is covered by 177402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollpatents owned by IBM, AT&T, and Mitsubishi. Hence arithmetic coding cannot 178402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molllegally be used without obtaining one or more licenses. For this reason, 179402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollsupport for arithmetic coding has been removed from the free JPEG software. 180402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll(Since arithmetic coding provides only a marginal gain over the unpatented 181402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollHuffman mode, it is unlikely that very many implementations will support it.) 182402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollSo far as we are aware, there are no patent restrictions on the remaining 183402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollcode. 184402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 185402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe IJG distribution formerly included code to read and write GIF files. 186402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollTo avoid entanglement with the Unisys LZW patent, GIF reading support has 187402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollbeen removed altogether, and the GIF writer has been simplified to produce 188402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll"uncompressed GIFs". This technique does not use the LZW algorithm; the 189402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollresulting GIF files are larger than usual, but are readable by all standard 190402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollGIF decoders. 191402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 192402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollWe are required to state that 193402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll "The Graphics Interchange Format(c) is the Copyright property of 194402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll CompuServe Incorporated. GIF(sm) is a Service Mark property of 195402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll CompuServe Incorporated." 196402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 197402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 198402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollREFERENCES 199402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll========== 200402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 201402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollWe highly recommend reading one or more of these references before trying to 202402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollunderstand the innards of the JPEG software. 203402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 204402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe best short technical introduction to the JPEG compression algorithm is 205402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll Wallace, Gregory K. "The JPEG Still Picture Compression Standard", 206402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. 207402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll(Adjacent articles in that issue discuss MPEG motion picture compression, 208402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollapplications of JPEG, and related topics.) If you don't have the CACM issue 209402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollhandy, a PostScript file containing a revised version of Wallace's article is 210402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollavailable at ftp://ftp.uu.net/graphics/jpeg/wallace.ps.gz. The file (actually 211402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molla preprint for an article that appeared in IEEE Trans. Consumer Electronics) 212402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollomits the sample images that appeared in CACM, but it includes corrections 213402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molland some added material. Note: the Wallace article is copyright ACM and IEEE, 214402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molland it may not be used for commercial purposes. 215402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 216402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollA somewhat less technical, more leisurely introduction to JPEG can be found in 217402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll"The Data Compression Book" by Mark Nelson and Jean-loup Gailly, published by 218402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollM&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. This book provides 219402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollgood explanations and example C code for a multitude of compression methods 220402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollincluding JPEG. It is an excellent source if you are comfortable reading C 221402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollcode but don't know much about data compression in general. The book's JPEG 222402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollsample code is far from industrial-strength, but when you are ready to look 223402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollat a full implementation, you've got one here... 224402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 225402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe best full description of JPEG is the textbook "JPEG Still Image Data 226402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollCompression Standard" by William B. Pennebaker and Joan L. Mitchell, published 227402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollby Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. Price US$59.95, 638 pp. 228402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe book includes the complete text of the ISO JPEG standards (DIS 10918-1 229402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molland draft DIS 10918-2). This is by far the most complete exposition of JPEG 230402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollin existence, and we highly recommend it. 231402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 232402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe JPEG standard itself is not available electronically; you must order a 233402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollpaper copy through ISO or ITU. (Unless you feel a need to own a certified 234402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollofficial copy, we recommend buying the Pennebaker and Mitchell book instead; 235402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollit's much cheaper and includes a great deal of useful explanatory material.) 236402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIn the USA, copies of the standard may be ordered from ANSI Sales at (212) 237402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll642-4900, or from Global Engineering Documents at (800) 854-7179. (ANSI 238402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molldoesn't take credit card orders, but Global does.) It's not cheap: as of 239402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll1992, ANSI was charging $95 for Part 1 and $47 for Part 2, plus 7% 240402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollshipping/handling. The standard is divided into two parts, Part 1 being the 241402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollactual specification, while Part 2 covers compliance testing methods. Part 1 242402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollis titled "Digital Compression and Coding of Continuous-tone Still Images, 243402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollPart 1: Requirements and guidelines" and has document numbers ISO/IEC IS 244402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of 245402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollContinuous-tone Still Images, Part 2: Compliance testing" and has document 246402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollnumbers ISO/IEC IS 10918-2, ITU-T T.83. 247402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 248402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollSome extensions to the original JPEG standard are defined in JPEG Part 3, 249402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molla newer ISO standard numbered ISO/IEC IS 10918-3 and ITU-T T.84. IJG 250402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollcurrently does not support any Part 3 extensions. 251402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 252402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe JPEG standard does not specify all details of an interchangeable file 253402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollformat. For the omitted details we follow the "JFIF" conventions, revision 254402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll1.02. A copy of the JFIF spec is available from: 255402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll Literature Department 256402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll C-Cube Microsystems, Inc. 257402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 1778 McCarthy Blvd. 258402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll Milpitas, CA 95035 259402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll phone (408) 944-6300, fax (408) 944-6314 260402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollA PostScript version of this document is available by FTP at 261402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollftp://ftp.uu.net/graphics/jpeg/jfif.ps.gz. There is also a plain text 262402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollversion at ftp://ftp.uu.net/graphics/jpeg/jfif.txt.gz, but it is missing 263402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollthe figures. 264402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 265402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe TIFF 6.0 file format specification can be obtained by FTP from 266402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. The JPEG incorporation scheme 267402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollfound in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. 268402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). 269402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollInstead, we recommend the JPEG design proposed by TIFF Technical Note #2 270402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll(Compression tag 7). Copies of this Note can be obtained from ftp.sgi.com or 271402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollfrom ftp://ftp.uu.net/graphics/jpeg/. It is expected that the next revision 272402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollof the TIFF spec will replace the 6.0 JPEG design with the Note's design. 273402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollAlthough IJG's own code does not support TIFF/JPEG, the free libtiff library 274402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molluses our library to implement TIFF/JPEG per the Note. libtiff is available 275402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollfrom ftp://ftp.sgi.com/graphics/tiff/. 276402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 277402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 278402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollARCHIVE LOCATIONS 279402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll================= 280402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 281402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe "official" archive site for this software is ftp.uu.net (Internet 282402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molladdress 192.48.96.9). The most recent released version can always be found 283402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollthere in directory graphics/jpeg. This particular version will be archived 284402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollas ftp://ftp.uu.net/graphics/jpeg/jpegsrc.v6b.tar.gz. If you don't have 285402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molldirect Internet access, UUNET's archives are also available via UUCP; contact 286402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollhelp@uunet.uu.net for information on retrieving files that way. 287402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 288402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollNumerous Internet sites maintain copies of the UUNET files. However, only 289402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollftp.uu.net is guaranteed to have the latest official version. 290402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 291402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollYou can also obtain this software in DOS-compatible "zip" archive format from 292402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollthe SimTel archives (ftp://ftp.simtel.net/pub/simtelnet/msdos/graphics/), or 293402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollon CompuServe in the Graphics Support forum (GO CIS:GRAPHSUP), library 12 294402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll"JPEG Tools". Again, these versions may sometimes lag behind the ftp.uu.net 295402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollrelease. 296402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 297402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe JPEG FAQ (Frequently Asked Questions) article is a useful source of 298402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollgeneral information about JPEG. It is updated constantly and therefore is 299402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollnot included in this distribution. The FAQ is posted every two weeks to 300402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollUsenet newsgroups comp.graphics.misc, news.answers, and other groups. 301402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIt is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ 302402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molland other news.answers archive sites, including the official news.answers 303402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollarchive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. 304402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIf you don't have Web or FTP access, send e-mail to mail-server@rtfm.mit.edu 305402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollwith body 306402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll send usenet/news.answers/jpeg-faq/part1 307402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll send usenet/news.answers/jpeg-faq/part2 308402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 309402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 310402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollRELATED SOFTWARE 311402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll================ 312402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 313402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollNumerous viewing and image manipulation programs now support JPEG. (Quite a 314402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollfew of them use this library to do so.) The JPEG FAQ described above lists 315402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollsome of the more popular free and shareware viewers, and tells where to 316402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollobtain them on Internet. 317402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 318402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIf you are on a Unix machine, we highly recommend Jef Poskanzer's free 319402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollPBMPLUS software, which provides many useful operations on PPM-format image 320402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollfiles. In particular, it can convert PPM images to and from a wide range of 321402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollother formats, thus making cjpeg/djpeg considerably more useful. The latest 322402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollversion is distributed by the NetPBM group, and is available from numerous 323402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollsites, notably ftp://wuarchive.wustl.edu/graphics/graphics/packages/NetPBM/. 324402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollUnfortunately PBMPLUS/NETPBM is not nearly as portable as the IJG software is; 325402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollyou are likely to have difficulty making it work on any non-Unix machine. 326402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 327402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollA different free JPEG implementation, written by the PVRG group at Stanford, 328402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollis available from ftp://havefun.stanford.edu/pub/jpeg/. This program 329402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollis designed for research and experimentation rather than production use; 330402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollit is slower, harder to use, and less portable than the IJG code, but it 331402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollis easier to read and modify. Also, the PVRG code supports lossless JPEG, 332402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollwhich we do not. (On the other hand, it doesn't do progressive JPEG.) 333402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 334402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 335402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollFILE FORMAT WARS 336402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll================ 337402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 338402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollSome JPEG programs produce files that are not compatible with our library. 339402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe root of the problem is that the ISO JPEG committee failed to specify a 340402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollconcrete file format. Some vendors "filled in the blanks" on their own, 341402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollcreating proprietary formats that no one else could read. (For example, none 342402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollof the early commercial JPEG implementations for the Macintosh were able to 343402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollexchange compressed files.) 344402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 345402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe file format we have adopted is called JFIF (see REFERENCES). This format 346402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollhas been agreed to by a number of major commercial JPEG vendors, and it has 347402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollbecome the de facto standard. JFIF is a minimal or "low end" representation. 348402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollWe recommend the use of TIFF/JPEG (TIFF revision 6.0 as modified by TIFF 349402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollTechnical Note #2) for "high end" applications that need to record a lot of 350402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molladditional data about an image. TIFF/JPEG is fairly new and not yet widely 351402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollsupported, unfortunately. 352402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 353402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe upcoming JPEG Part 3 standard defines a file format called SPIFF. 354402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollSPIFF is interoperable with JFIF, in the sense that most JFIF decoders should 355402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollbe able to read the most common variant of SPIFF. SPIFF has some technical 356402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molladvantages over JFIF, but its major claim to fame is simply that it is an 357402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollofficial standard rather than an informal one. At this point it is unclear 358402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollwhether SPIFF will supersede JFIF or whether JFIF will remain the de-facto 359402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollstandard. IJG intends to support SPIFF once the standard is frozen, but we 360402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollhave not decided whether it should become our default output format or not. 361402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll(In any case, our decoder will remain capable of reading JFIF indefinitely.) 362402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 363402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollVarious proprietary file formats incorporating JPEG compression also exist. 364402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollWe have little or no sympathy for the existence of these formats. Indeed, 365402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollone of the original reasons for developing this free software was to help 366402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollforce convergence on common, open format standards for JPEG files. Don't 367402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Molluse a proprietary file format! 368402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 369402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 370402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollTO DO 371402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll===== 372402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 373402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe major thrust for v7 will probably be improvement of visual quality. 374402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollThe current method for scaling the quantization tables is known not to be 375402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollvery good at low Q values. We also intend to investigate block boundary 376402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollsmoothing, "poor man's variable quantization", and other means of improving 377402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollquality-vs-file-size performance without sacrificing compatibility. 378402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 379402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollIn future versions, we are considering supporting some of the upcoming JPEG 380402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollPart 3 extensions --- principally, variable quantization and the SPIFF file 381402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Mollformat. 382402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 383402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollAs always, speeding things up is of great interest. 384402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael Moll 385402794e73aed8611d62eb4b01cd155e2d76fcb87Raphael MollPlease send bug reports, offers of help, etc. to jpeg-info@uunet.uu.net. 386