Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!samsung!dali.cs.montana.edu!milton!wiml
From: wiml@milton.u.washington.edu (William Lewis)
Newsgroups: alt.sources.d
Subject: Re: Compressing pictures
Summary: Colormaps
Message-ID: <7001@milton.u.washington.edu>
Date: 3 Sep 90 03:41:46 GMT
Organization: University of Washington, Seattle
Lines: 20

In various articles with different message-Ids, several people comment that
differencing only really makes sense over XORing if you're storing actual
RGB/HSB/whoknowswhat values rather than indices into a color map. I had
completely overlooked this in my earlier post =8) Since it seems (to me)
futile (to me) to try to sort triples into any sort of ascending/descending
order, maybe it would be better to have a separate colormap for each 
"color coordinate" (I don't know what they're *really* called ... the
R or the G or the B) and sort those indices. This could up to triple the
size of the *uncompressed* data, but might produce a smaller *compressed*
image. Or, it might not. Or, it might be a bad idea for some other reason.
I've become intrigued with this discussion anyway, and have already 
started digging out arithmetic compression stuff, so if anyone sees
any flaws in my basic reasoning I'd appreciate your telling me before
I write too much unusable code =8)
  And if all goes well I suppose I'll post a trial version to alt.sources
(see, this message does have something to do with this newsgroup) in a
few thousand years. Less if anyone wants to lend a hand.
-- 
wiml@milton.acs.washington.edu       Seattle, Washington  | No sig under
(William Lewis)   |  47 41' 15" N   122 42' 58" W  |||||||| construction