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diff --git a/README.djpeg b/README.djpeg new file mode 100644 index 0000000..8a456f9 --- /dev/null +++ b/README.djpeg @@ -0,0 +1,390 @@ +The JPEG decoder in SANE is taken mostly without change from The +Independent JPEG Group's JPEG software, release 6a. Their "djpeg.README" +file is included below. The only changes are to file names, e.g. +djpeg.c -> sanei_jpeg.c, and function names, +e.g. sanei_jpeg_start_output_ppm() + + +The Independent JPEG Group's JPEG software +========================================== + +README for release 6a of 7-Feb-96 +================================= + +This distribution contains the sixth public release of the Independent JPEG +Group's free JPEG software. You are welcome to redistribute this software and +to use it for any purpose, subject to the conditions under LEGAL ISSUES, below. + +Serious users of this software (particularly those incorporating it into +larger programs) should contact IJG at jpeg-info@uunet.uu.net to be added to +our electronic mailing list. Mailing list members are notified of updates +and have a chance to participate in technical discussions, etc. + +This software is the work of Tom Lane, Philip Gladstone, Luis Ortiz, Jim +Boucher, Lee Crocker, Julian Minguillon, George Phillips, Davide Rossi, +Ge' Weijers, and other members of the Independent JPEG Group. + +IJG is not affiliated with the official ISO JPEG standards committee. + + +DOCUMENTATION ROADMAP +===================== + +This file contains the following sections: + +OVERVIEW General description of JPEG and the IJG software. +LEGAL ISSUES Copyright, lack of warranty, terms of distribution. +REFERENCES Where to learn more about JPEG. +ARCHIVE LOCATIONS Where to find newer versions of this software. +RELATED SOFTWARE Other stuff you should get. +FILE FORMAT WARS Software *not* to get. +TO DO Plans for future IJG releases. + +Other documentation files in the distribution are: + +User documentation: + install.doc How to configure and install the IJG software. + usage.doc Usage instructions for cjpeg, djpeg, jpegtran, + rdjpgcom, and wrjpgcom. + *.1 Unix-style man pages for programs (same info as usage.doc). + wizard.doc Advanced usage instructions for JPEG wizards only. + change.log Version-to-version change highlights. +Programmer and internal documentation: + libjpeg.doc How to use the JPEG library in your own programs. + example.c Sample code for calling the JPEG library. + structure.doc Overview of the JPEG library's internal structure. + filelist.doc Road map of IJG files. + coderules.doc Coding style rules --- please read if you contribute code. + +Please read at least the files install.doc and usage.doc. Useful information +can also be found in the JPEG FAQ (Frequently Asked Questions) article. See +ARCHIVE LOCATIONS below to find out where to obtain the FAQ article. + +If you want to understand how the JPEG code works, we suggest reading one or +more of the REFERENCES, then looking at the documentation files (in roughly +the order listed) before diving into the code. + + +OVERVIEW +======== + +This package contains C software to implement JPEG image compression and +decompression. JPEG (pronounced "jay-peg") is a standardized compression +method for full-color and gray-scale images. JPEG is intended for compressing +"real-world" scenes; line drawings, cartoons and other non-realistic images +are not its strong suit. JPEG is lossy, meaning that the output image is not +exactly identical to the input image. Hence you must not use JPEG if you +have to have identical output bits. However, on typical photographic images, +very good compression levels can be obtained with no visible change, and +remarkably high compression levels are possible if you can tolerate a +low-quality image. For more details, see the references, or just experiment +with various compression settings. + +This software implements JPEG baseline, extended-sequential, and progressive +compression processes. Provision is made for supporting all variants of these +processes, although some uncommon parameter settings aren't implemented yet. +For legal reasons, we are not distributing code for the arithmetic-coding +variants of JPEG; see LEGAL ISSUES. We have made no provision for supporting +the hierarchical or lossless processes defined in the standard. + +We provide a set of library routines for reading and writing JPEG image files, +plus two sample applications "cjpeg" and "djpeg", which use the library to +perform conversion between JPEG and some other popular image file formats. +The library is intended to be reused in other applications. + +In order to support file conversion and viewing software, we have included +considerable functionality beyond the bare JPEG coding/decoding capability; +for example, the color quantization modules are not strictly part of JPEG +decoding, but they are essential for output to colormapped file formats or +colormapped displays. These extra functions can be compiled out of the +library if not required for a particular application. We have also included +"jpegtran", a utility for lossless transcoding between different JPEG +processes, and "rdjpgcom" and "wrjpgcom", two simple applications for +inserting and extracting textual comments in JFIF files. + +The emphasis in designing this software has been on achieving portability and +flexibility, while also making it fast enough to be useful. In particular, +the software is not intended to be read as a tutorial on JPEG. (See the +REFERENCES section for introductory material.) Rather, it is intended to +be reliable, portable, industrial-strength code. We do not claim to have +achieved that goal in every aspect of the software, but we strive for it. + +We welcome the use of this software as a component of commercial products. +No royalty is required, but we do ask for an acknowledgement in product +documentation, as described under LEGAL ISSUES. + + +LEGAL ISSUES +============ + +In plain English: + +1. We don't promise that this software works. (But if you find any bugs, + please let us know!) +2. You can use this software for whatever you want. You don't have to pay us. +3. You may not pretend that you wrote this software. If you use it in a + program, you must acknowledge somewhere in your documentation that + you've used the IJG code. + +In legalese: + +The authors make NO WARRANTY or representation, either express or implied, +with respect to this software, its quality, accuracy, merchantability, or +fitness for a particular purpose. This software is provided "AS IS", and you, +its user, assume the entire risk as to its quality and accuracy. + +This software is copyright (C) 1991-1996, Thomas G. Lane. +All Rights Reserved except as specified below. + +Permission is hereby granted to use, copy, modify, and distribute this +software (or portions thereof) for any purpose, without fee, subject to these +conditions: +(1) If any part of the source code for this software is distributed, then this +README file must be included, with this copyright and no-warranty notice +unaltered; and any additions, deletions, or changes to the original files +must be clearly indicated in accompanying documentation. +(2) If only executable code is distributed, then the accompanying +documentation must state that "this software is based in part on the work of +the Independent JPEG Group". +(3) Permission for use of this software is granted only if the user accepts +full responsibility for any undesirable consequences; the authors accept +NO LIABILITY for damages of any kind. + +These conditions apply to any software derived from or based on the IJG code, +not just to the unmodified library. If you use our work, you ought to +acknowledge us. + +Permission is NOT granted for the use of any IJG author's name or company name +in advertising or publicity relating to this software or products derived from +it. This software may be referred to only as "the Independent JPEG Group's +software". + +We specifically permit and encourage the use of this software as the basis of +commercial products, provided that all warranty or liability claims are +assumed by the product vendor. + + +ansi2knr.c is included in this distribution by permission of L. Peter Deutsch, +sole proprietor of its copyright holder, Aladdin Enterprises of Menlo Park, CA. +ansi2knr.c is NOT covered by the above copyright and conditions, but instead +by the usual distribution terms of the Free Software Foundation; principally, +that you must include source code if you redistribute it. (See the file +ansi2knr.c for full details.) However, since ansi2knr.c is not needed as part +of any program generated from the IJG code, this does not limit you more than +the foregoing paragraphs do. + +The configuration script "configure" was produced with GNU Autoconf. It +is copyright by the Free Software Foundation but is freely distributable. + +It appears that the arithmetic coding option of the JPEG spec is covered by +patents owned by IBM, AT&T, and Mitsubishi. Hence arithmetic coding cannot +legally be used without obtaining one or more licenses. For this reason, +support for arithmetic coding has been removed from the free JPEG software. +(Since arithmetic coding provides only a marginal gain over the unpatented +Huffman mode, it is unlikely that very many implementations will support it.) +So far as we are aware, there are no patent restrictions on the remaining +code. + +WARNING: Unisys has begun to enforce their patent on LZW compression against +GIF encoders and decoders. You will need a license from Unisys to use the +included rdgif.c or wrgif.c files in a commercial or shareware application. +At this time, Unisys is not enforcing their patent against freeware, so +distribution of this package remains legal. However, we intend to remove +GIF support from the IJG package as soon as a suitable replacement format +becomes reasonably popular. + +We are required to state that + "The Graphics Interchange Format(c) is the Copyright property of + CompuServe Incorporated. GIF(sm) is a Service Mark property of + CompuServe Incorporated." + + +REFERENCES +========== + +We highly recommend reading one or more of these references before trying to +understand the innards of the JPEG software. + +The best short technical introduction to the JPEG compression algorithm is + Wallace, Gregory K. "The JPEG Still Picture Compression Standard", + Communications of the ACM, April 1991 (vol. 34 no. 4), pp. 30-44. +(Adjacent articles in that issue discuss MPEG motion picture compression, +applications of JPEG, and related topics.) If you don't have the CACM issue +handy, a PostScript file containing a revised version of Wallace's article +is available at ftp.uu.net, graphics/jpeg/wallace.ps.gz. The file (actually +a preprint for an article that appeared in IEEE Trans. Consumer Electronics) +omits the sample images that appeared in CACM, but it includes corrections +and some added material. Note: the Wallace article is copyright ACM and +IEEE, and it may not be used for commercial purposes. + +A somewhat less technical, more leisurely introduction to JPEG can be found in +"The Data Compression Book" by Mark Nelson, published by M&T Books (Redwood +City, CA), 1991, ISBN 1-55851-216-0. This book provides good explanations and +example C code for a multitude of compression methods including JPEG. It is +an excellent source if you are comfortable reading C code but don't know much +about data compression in general. The book's JPEG sample code is far from +industrial-strength, but when you are ready to look at a full implementation, +you've got one here... + +The best full description of JPEG is the textbook "JPEG Still Image Data +Compression Standard" by William B. Pennebaker and Joan L. Mitchell, published +by Van Nostrand Reinhold, 1993, ISBN 0-442-01272-1. Price US$59.95, 638 pp. +The book includes the complete text of the ISO JPEG standards (DIS 10918-1 +and draft DIS 10918-2). This is by far the most complete exposition of JPEG +in existence, and we highly recommend it. + +The JPEG standard itself is not available electronically; you must order a +paper copy through ISO or ITU. (Unless you feel a need to own a certified +official copy, we recommend buying the Pennebaker and Mitchell book instead; +it's much cheaper and includes a great deal of useful explanatory material.) +In the USA, copies of the standard may be ordered from ANSI Sales at (212) +642-4900, or from Global Engineering Documents at (800) 854-7179. (ANSI +doesn't take credit card orders, but Global does.) It's not cheap: as of +1992, ANSI was charging $95 for Part 1 and $47 for Part 2, plus 7% +shipping/handling. The standard is divided into two parts, Part 1 being the +actual specification, while Part 2 covers compliance testing methods. Part 1 +is titled "Digital Compression and Coding of Continuous-tone Still Images, +Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS +10918-1, ITU-T T.81. Part 2 is titled "Digital Compression and Coding of +Continuous-tone Still Images, Part 2: Compliance testing" and has document +numbers ISO/IEC IS 10918-2, ITU-T T.83. + +Extensions to the original JPEG standard are defined in JPEG Part 3, a new ISO +document. Part 3 is undergoing ISO balloting and is expected to be approved +by the end of 1995; it will have document numbers ISO/IEC IS 10918-3, ITU-T +T.84. IJG currently does not support any Part 3 extensions. + +The JPEG standard does not specify all details of an interchangeable file +format. For the omitted details we follow the "JFIF" conventions, revision +1.02. A copy of the JFIF spec is available from: + Literature Department + C-Cube Microsystems, Inc. + 1778 McCarthy Blvd. + Milpitas, CA 95035 + phone (408) 944-6300, fax (408) 944-6314 +A PostScript version of this document is available at ftp.uu.net, file +graphics/jpeg/jfif.ps.gz. It can also be obtained by e-mail from the C-Cube +mail server, netlib@c3.pla.ca.us. Send the message "send jfif_ps from jpeg" +to the server to obtain the JFIF document; send the message "help" if you have +trouble. + +The TIFF 6.0 file format specification can be obtained by FTP from sgi.com +(192.48.153.1), file graphics/tiff/TIFF6.ps.Z; or you can order a printed +copy from Aldus Corp. at (206) 628-6593. The JPEG incorporation scheme +found in the TIFF 6.0 spec of 3-June-92 has a number of serious problems. +IJG does not recommend use of the TIFF 6.0 design (TIFF Compression tag 6). +Instead, we recommend the JPEG design proposed by TIFF Technical Note #2 +(Compression tag 7). Copies of this Note can be obtained from sgi.com or +from ftp.uu.net:/graphics/jpeg/. It is expected that the next revision of +the TIFF spec will replace the 6.0 JPEG design with the Note's design. +Although IJG's own code does not support TIFF/JPEG, the free libtiff library +uses our library to implement TIFF/JPEG per the Note. libtiff is available +from sgi.com:/graphics/tiff/. + + +ARCHIVE LOCATIONS +================= + +The "official" archive site for this software is ftp.uu.net (Internet +address 192.48.96.9). The most recent released version can always be found +there in directory graphics/jpeg. This particular version will be archived +as graphics/jpeg/jpegsrc.v6a.tar.gz. If you are on the Internet, you +can retrieve files from ftp.uu.net by standard anonymous FTP. If you don't +have FTP access, UUNET's archives are also available via UUCP; contact +help@uunet.uu.net for information on retrieving files that way. + +Numerous Internet sites maintain copies of the UUNET files. However, only +ftp.uu.net is guaranteed to have the latest official version. + +You can also obtain this software in DOS-compatible "zip" archive format from +the SimTel archives (ftp.coast.net:/SimTel/msdos/graphics/), or on CompuServe +in the Graphics Support forum (GO CIS:GRAPHSUP), library 12 "JPEG Tools". +Again, these versions may sometimes lag behind the ftp.uu.net release. + +The JPEG FAQ (Frequently Asked Questions) article is a useful source of +general information about JPEG. It is updated constantly and therefore is +not included in this distribution. The FAQ is posted every two weeks to +Usenet newsgroups comp.graphics.misc, news.answers, and other groups. +You can always obtain the latest version from the news.answers archive at +rtfm.mit.edu. By FTP, fetch /pub/usenet/news.answers/jpeg-faq/part1 and +.../part2. If you don't have FTP, send e-mail to mail-server@rtfm.mit.edu +with body + send usenet/news.answers/jpeg-faq/part1 + send usenet/news.answers/jpeg-faq/part2 + + +RELATED SOFTWARE +================ + +Numerous viewing and image manipulation programs now support JPEG. (Quite a +few of them use this library to do so.) The JPEG FAQ described above lists +some of the more popular free and shareware viewers, and tells where to +obtain them on Internet. + +If you are on a Unix machine, we highly recommend Jef Poskanzer's free +PBMPLUS image software, which provides many useful operations on PPM-format +image files. In particular, it can convert PPM images to and from a wide +range of other formats. You can obtain this package by FTP from ftp.x.org +(contrib/pbmplus*.tar.Z) or ftp.ee.lbl.gov (pbmplus*.tar.Z). There is also +a newer update of this package called NETPBM, available from +wuarchive.wustl.edu under directory /graphics/graphics/packages/NetPBM/. +Unfortunately PBMPLUS/NETPBM is not nearly as portable as the IJG software +is; you are likely to have difficulty making it work on any non-Unix machine. + +A different free JPEG implementation, written by the PVRG group at Stanford, +is available from havefun.stanford.edu in directory pub/jpeg. This program +is designed for research and experimentation rather than production use; +it is slower, harder to use, and less portable than the IJG code, but it +is easier to read and modify. Also, the PVRG code supports lossless JPEG, +which we do not. + + +FILE FORMAT WARS +================ + +Some JPEG programs produce files that are not compatible with our library. +The root of the problem is that the ISO JPEG committee failed to specify a +concrete file format. Some vendors "filled in the blanks" on their own, +creating proprietary formats that no one else could read. (For example, none +of the early commercial JPEG implementations for the Macintosh were able to +exchange compressed files.) + +The file format we have adopted is called JFIF (see REFERENCES). This format +has been agreed to by a number of major commercial JPEG vendors, and it has +become the de facto standard. JFIF is a minimal or "low end" representation. +We recommend the use of TIFF/JPEG (TIFF revision 6.0 as modified by TIFF +Technical Note #2) for "high end" applications that need to record a lot of +additional data about an image. TIFF/JPEG is fairly new and not yet widely +supported, unfortunately. + +The upcoming JPEG Part 3 standard defines a file format called SPIFF. +SPIFF is interoperable with JFIF, in the sense that most JFIF decoders should +be able to read the most common variant of SPIFF. SPIFF has some technical +advantages over JFIF, but its major claim to fame is simply that it is an +official standard rather than an informal one. At this point it is unclear +whether SPIFF will supersede JFIF or whether JFIF will remain the de-facto +standard. IJG intends to support SPIFF once the standard is frozen, but we +have not decided whether it should become our default output format or not. +(In any case, our decoder will remain capable of reading JFIF indefinitely.) + +Various proprietary file formats incorporating JPEG compression also exist. +We have little or no sympathy for the existence of these formats. Indeed, +one of the original reasons for developing this free software was to help +force convergence on common, open format standards for JPEG files. Don't +use a proprietary file format! + + +TO DO +===== + +In future versions, we are considering supporting some of the upcoming JPEG +Part 3 extensions --- principally, variable quantization and the SPIFF file +format. + +Tuning the software for better behavior at low quality/high compression +settings is also of interest. The current method for scaling the +quantization tables is known not to be very good at low Q values. + +As always, speeding things up is high on our priority list. + +Please send bug reports, offers of help, etc. to jpeg-info@uunet.uu.net. |