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 tounderstand 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 issuehandy, a PostScript file containing a revised version of Wallace's article isavailable at ftp://ftp.uu.net/graphics/jpeg/wallace.ps.gz.  The file (actuallya preprint for an article that appeared in IEEE Trans. Consumer Electronics)omits the sample images that appeared in CACM, but it includes correctionsand 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 byM&T Books (New York), 2nd ed. 1996, ISBN 1-55851-434-1.  This book providesgood explanations and example C code for a multitude of compression methodsincluding JPEG.  It is an excellent source if you are comfortable reading Ccode but don't know much about data compression in general.  The book's JPEGsample code is far from industrial-strength, but when you are ready to lookat a full implementation, you've got one here...The best full description of JPEG is the textbook "JPEG Still Image DataCompression Standard" by William B. Pennebaker and Joan L. Mitchell, publishedby 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 10918-1and draft DIS 10918-2).  This is by far the most complete exposition of JPEGin existence, and we highly recommend it.The JPEG standard itself is not available electronically; you must order apaper copy through ISO or ITU.  (Unless you feel a need to own a certifiedofficial 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.  (ANSIdoesn't take credit card orders, but Global does.)  It's not cheap: as of1992, 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 theactual specification, while Part 2 covers compliance testing methods.  Part 1is titled "Digital Compression and Coding of Continuous-tone Still Images,Part 1: Requirements and guidelines" and has document numbers ISO/IEC IS10918-1, ITU-T T.81.  Part 2 is titled "Digital Compression and Coding ofContinuous-tone Still Images, Part 2: Compliance testing" and has documentnumbers ISO/IEC IS 10918-2, ITU-T T.83.Some extensions to the original JPEG standard are defined in JPEG Part 3,a newer ISO standard numbered ISO/IEC IS 10918-3 and ITU-T T.84.  IJGcurrently does not support any Part 3 extensions.The JPEG standard does not specify all details of an interchangeable fileformat.  For the omitted details we follow the "JFIF" conventions, revision1.02.  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) 944-6314A PostScript version of this document is available by FTP atftp://ftp.uu.net/graphics/jpeg/jfif.ps.gz.  There is also a plain textversion at ftp://ftp.uu.net/graphics/jpeg/jfif.txt.gz, but it is missingthe figures.The TIFF 6.0 file format specification can be obtained by FTP fromftp://ftp.sgi.com/graphics/tiff/TIFF6.ps.gz.  The JPEG incorporation schemefound 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 ftp.sgi.com orfrom ftp://ftp.uu.net/graphics/jpeg/.  It is expected that the next revisionof 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 libraryuses our library to implement TIFF/JPEG per the Note.  libtiff is availablefrom ftp://ftp.sgi.com/graphics/tiff/.ARCHIVE LOCATIONS=================The "official" archive site for this software is ftp.uu.net (Internetaddress 192.48.96.9).  The most recent released version can always be foundthere in directory graphics/jpeg.  This particular version will be archivedas ftp://ftp.uu.net/graphics/jpeg/jpegsrc.v6b.tar.gz.  If you don't havedirect Internet access, UUNET's archives are also available via UUCP; contacthelp@uunet.uu.net for information on retrieving files that way.Numerous Internet sites maintain copies of the UUNET files.  However, onlyftp.uu.net is guaranteed to have the latest official version.You can also obtain this software in DOS-compatible "zip" archive format fromthe SimTel archives (ftp://ftp.simtel.net/pub/simtelnet/msdos/graphics/), oron CompuServe in the Graphics Support forum (GO CIS:GRAPHSUP), library 12"JPEG Tools".  Again, these versions may sometimes lag behind the ftp.uu.netrelease.The JPEG FAQ (Frequently Asked Questions) article is a useful source ofgeneral information about JPEG.  It is updated constantly and therefore isnot included in this distribution.  The FAQ is posted every two weeks toUsenet newsgroups comp.graphics.misc, news.answers, and other groups.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.answersarchive 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.eduwith body	send usenet/news.answers/jpeg-faq/part1	send usenet/news.answers/jpeg-faq/part2RELATED SOFTWARE================Numerous viewing and image manipulation programs now support JPEG.  (Quite afew of them use this library to do so.)  The JPEG FAQ described above listssome of the more popular free and shareware viewers, and tells where toobtain them on Internet.If you are on a Unix machine, we highly recommend Jef Poskanzer's freePBMPLUS software, which provides many useful operations on PPM-format imagefiles.  In particular, it can convert PPM images to and from a wide range ofother formats, thus making cjpeg/djpeg considerably more useful.  The latestversion is distributed by the NetPBM group, and is available from numeroussites, notably ftp://wuarchive.wustl.edu/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 ftp://havefun.stanford.edu/pub/jpeg/.  This programis designed for research and experimentation rather than production use;it is slower, harder to use, and less portable than the IJG code, but itis easier to read and modify.  Also, the PVRG code supports lossless JPEG,which we do not.  (On the other hand, it doesn't do progressive JPEG.)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 aconcrete file format.  Some vendors "filled in the blanks" on their own,creating proprietary formats that no one else could read.  (For example, noneof the early commercial JPEG implementations for the Macintosh were able toexchange compressed files.)The file format we have adopted is called JFIF (see REFERENCES).  This formathas been agreed to by a number of major commercial JPEG vendors, and it hasbecome 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 TIFFTechnical Note #2) for "high end" applications that need to record a lot ofadditional data about an image.  TIFF/JPEG is fairly new and not yet widelysupported, 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 shouldbe able to read the most common variant of SPIFF.  SPIFF has some technicaladvantages over JFIF, but its major claim to fame is simply that it is anofficial standard rather than an informal one.  At this point it is unclearwhether SPIFF will supersede JFIF or whether JFIF will remain the de-factostandard.  IJG intends to support SPIFF once the standard is frozen, but wehave 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 helpforce convergence on common, open format standards for JPEG files.  Don'tuse a proprietary file format!TO DO=====The major thrust for v7 will probably be improvement of visual quality.The current method for scaling the quantization tables is known not to bevery good at low Q values.  We also intend to investigate block boundarysmoothing, "poor man's variable quantization", and other means of improvingquality-vs-file-size performance without sacrificing compatibility.In future versions, we are considering supporting some of the upcoming JPEGPart 3 extensions --- principally, variable quantization and the SPIFF fileformat.As always, speeding things up is of great interest.Please send bug reports, offers of help, etc. to jpeg-info@uunet.uu.net.