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Date: Thu, 11 Feb 1999 13:09:07 -0500
From: Frank Warmerdam <warmerda@home.com>
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To: TIFF Mailing List <tiff@olympiakos.com>
Cc: Ian Macleod <ian.macleod@geosoft.com>,
        Roger Amorim <roger.amorim@geosoft.com>
Subject: LZW Encoding and Decoding
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Folks,

The LZW issue has been extensively discussed with regard to GIF (which also
uses it).  On the GIFLIB web page (http://prtr-13.ucsc.edu/~badger/software/giflib.shtml) I see:

``Patent lawyers seem to agree that the wording of the Unisys patent is such 
that code which does decoding only (and not encoding) is not covered by the 
patent, so you may be safe using this library. [Note: Unisys has at times 
expressed views which seem to disagree with this interpretation. If you're 
concerned, speak to a lawyer yourself.]''

The page ``The GIF Controversy: A Software Developer's Perspective'' may also
be of interest:

  http://www.cloanto.com/users/mcb/19950127giflzw.html

I would suggest that applications written with libtiff should not allow users
to compress with LZW if you want to be safe, but that allowing the
decompression should be safe.  

Best regards,

---------------------------------------+--------------------------------------
I set the clouds in motion - turned up | Frank Warmerdam, Programmer for Rent
light and sound - activate the windows | http://members.home.com/warmerda
and watch the world go round - Rush    | warmerda@home.com
