Re: LZW

[jm59@prism.gatech.edu (John M. Mills)]

haseltine@onramp.net (Doug Haseltine) writes:
>"Vicious" <vicious@hol.fr> wrote:
>>Anyone can tell me where I can find LZW ada source?

>Sir:
>We did a search a couple years ago when we had a such a need
>and could not found any public source.
 ...
>It worked fine for our purposes
>(compressing some boot code into non-volatile memory, and
>transferring compressed downloadable images when upgrading
>embedded software), but perhaps you'll have better luck
>finding a clean port.

I would be cautious about incorporating LZW into a current development, due
to patent considerations.  The following paragraphs are excerpted from
ftp://rtfm.mit.edu/pub/usenet/comp.answers/graphics/fileformats-faq/part1:
***
...(much material elided)...
"Subject: 1. Is it now illegal to use CompuServe's GIF format?

"It is not illegal to own, transmit, or receive GIF files (provided that no
unlicensed compression and/or decompression of the files occurs). You must
realize, however, that GIF files are not the issue. The issue is, in fact,
the LZW data compression algorithm.

"In 1984, while working for Sperry Corporation, Terry Welch modified the
Lempel-Ziv 78 (LZ78) compression algorithm for greater efficiency for
implementation in high-performance disk controllers. The result was the
LZW algorithm. The world was informed of the existence of LZW by the
following journal article, published by Mr. Welch after he left the
employment of Sperry:

  Welch, T. A., "A Technique for High Performance Data Compression,"
  IEEE Computer, Volume 17, Number 6, June 1984.

"In 1985, Sperry Corporation was granted a patent (4,558,302) for the Welch
invention and implementation of the LZW data compression algorithm. Since
that time, this LZW patent has been publicly available for all to see in
the US Patent Office and many public libraries, and is available through
many on-line services."

...(balance of FAQ elided)...
***

I am sorry to contribute 'FUD' (Fear-Uncertainty-Doubt) here, but the issue
of the LWZ patent is widely mentioned.  I would _certainly_ seek legal advice
before incorporating it into any application where I was unsure of Sperry's
patent and license applicability.  I'm surprised no one else mentioned this,
and would be happy to receive more current and/or authoritative information
on the subject.  In any case, I would be cautious.

Thanks -- john mills




-- 
 John M. Mills, Senior Research Engineer   --   john.mills@gtri.gatech.edu
   Georgia Tech Research Institute, Georgia Tech, Atlanta, GA 30332-0834
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