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From: roy@phri.UUCP (Roy Smith)
Newsgroups: comp.graphics
Subject: Re: Chaotic Compression
Message-ID: <3028@phri.UUCP>
Date: Fri, 13-Nov-87 22:18:50 EST
Article-I.D.: phri.3028
Posted: Fri Nov 13 22:18:50 1987
Date-Received: Sun, 15-Nov-87 12:08:59 EST
References: <619@applix.UUCP>
Reply-To: roy@phri.UUCP (Roy Smith)
Organization: Public Health Research Inst. (NY, NY)
Lines: 20

In article <619@applix.UUCP> scott@applix.UUCP (Scott Evernden) writes:

	I couldn't derive the math, but one can calculate the amount of
information in a given image (quantified in bits) and it is theoretically
impossible to compress it past that.  How close you get to that ideal
depends on the compression algorithm you use.

	We often use compress 4.0 (you know, the one that comes with 2.11
news) to compress Sun screendumps and get 99.9+% compression.  Of course,
the images we are compressing are very sparse (typically the result of a
line drawing in a full-screen tektool window).  It is interesting to note
that if you take one of these screendump files and run it through "od"
(octal dump; turns each 8-bit byte into a 3-digit octal number), and
compress the output, you get almost exactly the same size file as if you
compressed the original bitmap.  Makes sense, considering that the amount
of information hasn't changed any.
-- 
Roy Smith, {allegra,cmcl2,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, Nara )y f