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(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. 

 

The IJG distribution formerly included code to read and write GIF files. 

To avoid entanglement with the Unisys LZW patent, 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 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://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 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 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