Re: compression methods

[Alex Wulms]

] >     *And now, my spamming against the copyright (claimers) owners
] > of the shrink algorithm. Since 1987, Compuserve has spread a new
] > image file format, the very well known GIF. It uses an algorithm
] > named Lempel-Ziv-Huffman (LZH).
] 
] Errata: GIF uses LZW (Lempel, Ziv  &  Welch) method.
This is correct. LZW is the first efficient implementation of the LZ78 
algorithm (published by Lempel and Ziv in 1978). The LZW implementation has 
been done by Welch somewhere in the beginning of the 80's, who was working 
for AT&T in those days. They filed for a patent something like one year after 
they published the implementation in a public paper. This patent has never 
been granted in Europe, only in the US. In Europe, it is not possible to 
request a patent AFTER you have published something in a public paper, 
conference proceeding or whatever. In the US it is.

Anyway, old compressors like ARC on CP/M, MSX and MS-DOS (not to be confused 
with LHARC!), and compress on UNIX are based on the LZW implementation. And 
ofcourse the GIF format is also based on the LZW algorithm.

Newer compressors, like ZIP, ARJ and LHARC are based on another algorithm 
described by Lempel and Ziv. This algorithm, called LZ77, was first published 
in 1977. It can achieve higher compression ratios then the LZ78 algorithm. 
Though it is much more difficult to come up with a fast and efficient 
implementation. Hence, the LZ78 algorithm was implemented years before the 
LZ77 algorithm...


Kind regards,
Alex Wulms


-- 
Alex Wulms/XelaSoft - MSX of anders NIX - Linux 4 ever
See my homepage for info on the  *** XSA *** format
http://www.inter.nl.net/users/A.P.Wulms



****
MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put
in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the
quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
****