Just to give some missed details.
Drew Daniels
---------- Forwarded message ----------
Date: Thu, 13 Feb 2003 09:55:30 -0800
From: Charles Bloom <[EMAIL PROTECTED]>
To: Drew Scott Daniels <[EMAIL PROTECTED]>,
Magnus Ekdahl <[EMAIL PROTECTED]>
Subject: Re: PPM compression algorithms.
Hi guys, a few notes :
PPMZ was never really intended for direct use in production software;
it's more of a test-bed. For example, it was never really optimized.
Malcolm Taylor took a lot of the ideas of PPMZ and put them in RKive,
which is very fast. Also, the so-called "PPMd" and PPMii are based on
PPMZ, and are more finely tweaked and optimized.
PPMii is very good; it's similar to PPMZ but tweaked and improved in
various ways. The biggest difference is that he is doing a bit of
"Context mixing and blending" across contexts which are not directly
linked in the Markov chain.
PPMd - I don't think there are any actual papers on. This is NOT the
"PPMD" algorithm of Bill Teahan, so it's somewhat mis-named. I believe
it's very similar to PPMZ, but with some tweaks and special custom support
for text files and binaries.
>Charles Bloom: Do you know why PPMd is performing better? Do you have any
>suggestions for code that would be useful for me? I'd like to license my
>code later like Ogg, gzip, zip and bzip2 so that it can be used in
>commercial applications. Are you still developing PPMZ(2) or any other
>compressors?
I'm no longer actively working in compression; I haven't really touched the
PPMZ's in several years. In modern stuff, PPMd is obviously good. The
primary algorithms in this area are PPMZ and PPMii ; there are implementations
like BOA and PPMonstr that are very good, and many more.
-------------------------------------------------------
Charles Bloom [EMAIL PROTECTED] http://www.cbloom.com
