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From: tgl@g.gp.cs.cmu.edu (Tom Lane)
Newsgroups: comp.graphics
Subject: Re: Need JPEG and/or MPEG formats
Keywords: JPEG MPEG
Message-ID: <12252@pt.cs.cmu.edu>
Date: 6 Mar 91 16:14:11 GMT
References: <1991Mar6.002423.3038@unicorn.cc.wwu.edu> <1991Mar06.114149.14240@cs.ruu.nl>
Organization: Carnegie-Mellon University, CS/RI
Lines: 41

>>Does anyone know where to get a document describing the file format for JPEG?
>>Is it even available?  An ftp source would be ideal.
> 
> Does anyone know the ALGORITHMS for JPEG/MPEG compression and decompression?

As far as I know, the JPEG spec is not available on-line anywhere.
(If anyone finds out different, please let me know!)

You can order a paper copy of the spec from the ANSI X3 secretariat.  Write to:
    Attn: JPEG Draft Technical Specification
    X3 Secretariat: Computer and Business Equipment Manufacturers Association
    311 First Street NW, Suite 500
    Washington, DC 20001-2178
Enclose a check for $8.00 made out to X3 Secretariat.  Say somewhere in your
letter that you want the document for review and comment.

However, I don't recommend that everybody order a copy.  For one thing, they
seem to have just one overworked secretary Xeroxing these copies.

For another, the JPEG algorithm is not simple nor easy to implement.  Unless
you already know something about color space conversion, discrete cosine
transforms, Huffman and arithmetic coding, you'll not learn much from
reading the draft spec.

For a third thing, the draft spec actually defines a family of compression
algorithms, not a specific file format.  If you try to implement from just
the draft spec, you will most likely find yourself unable to exchange
compressed files with other implementations.


I am running a group of volunteers that is writing a free, portable
implementation of the JPEG algorithm.  We expect to release something in
a couple months' time.  (On the other hand, I said that a couple months
ago, so don't hold your breath.)  I recommend that everybody sit tight
and wait for our code, rather than trying to build your own versions.

If you'd like to help out, we could still use some more volunteers.

-- 
			tom lane
Internet: tgl@cs.cmu.edu	BITNET: tgl%cs.cmu.edu@cmuccvma