Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!rutgers!cmcl2!kramden.acf.nyu.edu!brnstnd
From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.compression
Subject: LZW is *not* safe to use
Summary: IBM holds an earlier patent on LZW
Message-ID: <29014:Apr215:25:5191@kramden.acf.nyu.edu>
Date: 2 Apr 91 15:25:51 GMT
References: <1991Mar25.215830.5200@nntp-server.caltech.edu> <JAFFER.91Mar27002238@michael.ai.mit.edu> <1991Apr2.003452.27382@alembic.acs.com>
Organization: IR
Lines: 20

In article <1991Apr2.003452.27382@alembic.acs.com> csu@alembic.acs.com (Dave Mack) writes:
> Except that the patent-holder (Unisys, I believe)

There are *two* patent holders on LZW: Unisys, through Welch's patent,
and IBM, through the Miller-Wegman patent. The IBM patent covers LZW,
among other things, and was filed earlier than the Sperry patent. (Yes,
this does mean the Sperry patent should not have been approved.)

It is *not* safe to use LZW. Unisys has been throwing disclaimers left
and right for money it won't get. Despite the current market situation
and various unfounded rumors, IBM has rights to LZW, and it hasn't
disclaimed anything.

> There is *no* problem with using software implementations of
> LZW compression for anything, be it GIF encoding or news transport.

No. There is a huge problem with all implementations of LZW, and the
problem won't go away until 2006.

---Dan