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diff --git a/media/libjpeg/README.ijg b/media/libjpeg/README.ijg new file mode 100644 index 000000000..9c450ceb0 --- /dev/null +++ b/media/libjpeg/README.ijg @@ -0,0 +1,279 @@ +libjpeg-turbo note: This file has been modified by The libjpeg-turbo Project +to include only information relevant to libjpeg-turbo, to wordsmith certain +sections, and to remove impolitic language that existed in the libjpeg v8 +README. It is included only for reference. Please see README.md for +information specific to libjpeg-turbo. + + +The Independent JPEG Group's JPEG software +========================================== + +This distribution contains a 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. + +This software is the work of Tom Lane, Guido Vollbeding, Philip Gladstone, +Bill Allombert, Jim Boucher, Lee Crocker, Bob Friesenhahn, Ben Jackson, +Julian Minguillon, Luis Ortiz, George Phillips, Davide Rossi, Ge' Weijers, +and other members of the Independent JPEG Group. + +IJG is not affiliated with the ISO/IEC JTC1/SC29/WG1 standards committee +(also known as JPEG, together with ITU-T SG16). + + +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. +FILE FORMAT WARS Software *not* to get. +TO DO Plans for future IJG releases. + +Other documentation files in the distribution are: + +User documentation: + usage.txt Usage instructions for cjpeg, djpeg, jpegtran, + rdjpgcom, and wrjpgcom. + *.1 Unix-style man pages for programs (same info as usage.txt). + wizard.txt Advanced usage instructions for JPEG wizards only. + change.log Version-to-version change highlights. +Programmer and internal documentation: + libjpeg.txt How to use the JPEG library in your own programs. + example.c Sample code for calling the JPEG library. + structure.txt Overview of the JPEG library's internal structure. + coderules.txt Coding style rules --- please read if you contribute code. + +Please read at least usage.txt. Some 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 encoding, decoding, +and transcoding. JPEG (pronounced "jay-peg") is a standardized compression +method for full-color and grayscale images. JPEG's strong suit is compressing +photographic images or other types of images that have smooth color and +brightness transitions between neighboring pixels. Images with sharp lines or +other abrupt features may not compress well with JPEG, and a higher JPEG +quality may have to be used to avoid visible compression artifacts with such +images. + +JPEG is lossy, meaning that the output pixels are not necessarily identical to +the input pixels. However, on photographic content and other "smooth" images, +very good compression ratios can be obtained with no visible compression +artifacts, and extremely high compression ratios are possible if you are +willing to sacrifice image quality (by reducing the "quality" setting in the +compressor.) + +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. +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) 1991-2016, Thomas G. Lane, Guido Vollbeding. +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. + + +The Unix configuration script "configure" was produced with GNU Autoconf. +It is copyright by the Free Software Foundation but is freely distributable. +The same holds for its supporting scripts (config.guess, config.sub, +ltmain.sh). Another support script, install-sh, is copyright by X Consortium +but is also freely distributable. + +The IJG distribution formerly included code to read and write GIF files. +To avoid entanglement with the Unisys LZW patent (now expired), GIF reading +support has been removed altogether, and the GIF writer has been simplified +to produce "uncompressed GIFs". This technique does not use the LZW +algorithm; the resulting GIF files are larger than usual, but are readable +by all standard GIF decoders. + +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 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 PDF file containing a revised version of Wallace's article is +available at http://www.ijg.org/files/Wallace.JPEG.pdf. 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 and Jean-loup Gailly, published by +M&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1. 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 currently available 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). + +The original JPEG 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. + +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. JFIF 1.02 has been adopted as an Ecma International Technical Report +and thus received a formal publication status. It is available as a free +download in PDF format from +http://www.ecma-international.org/publications/techreports/E-TR-098.htm. +A PostScript version of the JFIF document is available at +http://www.ijg.org/files/jfif.ps.gz. There is also a plain text version at +http://www.ijg.org/files/jfif.txt.gz, but it is missing the figures. + +The TIFF 6.0 file format specification can be obtained by FTP from +ftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz. 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 +http://www.ijg.org/files/. 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. + + +ARCHIVE LOCATIONS +================= + +The "official" archive site for this software is www.ijg.org. +The most recent released version can always be found there in +directory "files". + +The JPEG FAQ (Frequently Asked Questions) article is a source of some +general information about JPEG. +It is available on the World Wide Web at http://www.faqs.org/faqs/jpeg-faq/ +and other news.answers archive sites, including the official news.answers +archive at rtfm.mit.edu: ftp://rtfm.mit.edu/pub/usenet/news.answers/jpeg-faq/. +If you don't have Web or FTP access, 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 + + +FILE FORMAT WARS +================ + +The ISO/IEC JTC1/SC29/WG1 standards committee (also known as JPEG, together +with ITU-T SG16) currently promotes different formats containing the name +"JPEG" which are incompatible with original DCT-based JPEG. IJG therefore does +not support these formats (see REFERENCES). Indeed, one of the original +reasons for developing this free software was to help force convergence on +common, interoperable format standards for JPEG files. +Don't use an incompatible file format! +(In any case, our decoder will remain capable of reading existing JPEG +image files indefinitely.) + + +TO DO +===== + +Please send bug reports, offers of help, etc. to jpeg-info@jpegclub.org. |