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From: warnock@stars.gsfc.nasa.gov (Archie Warnock)
Newsgroups: comp.compression
Subject: Re: Atronomical data compression
Keywords: Spectra, Keck
Message-ID: <4638@dftsrv.gsfc.nasa.gov>
Date: 27 Mar 91 16:21:51 GMT
References: <1991Mar23.013557.28151@nntp-server.caltech.edu> <1991Mar27.021241.6339@magnus.acs.ohio-state.edu>
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In article <1991Mar27.021241.6339@magnus.acs.ohio-state.edu>,
henden@hpuxa.acs.ohio-state.edu (Arne A. Henden) writes... 
>  One technique that we wanted to try, but have never taken
>the time to program, is to use bit plane compression.  For the

Hi Arne :-)  Long time, eh?

I've looked into a variant on this idea - just by dividing the image 
into the high- and low-order bytes and comparing the compression factor 
this way with that for the entire (virgin) image.  Used a couple of 
standard PC-type compression programs like PKZIP.  It helped, but not as 
much as I'd have hoped.  Typically, the resulting compressed images were 
about 10% - 15% smaller than if I just left the image alone.  You might 
do better by breaking things up into individual bit-planes, but the last 
few planes would be so noisy, you might not.  Bottom line seems to be 
that it's easy (and fairly fast) to get the first 50% or so.  Recoding 
from 16-bit numbers to 8-bit differences gets you that much, and only 
costs a single addition per pixel to restore.  The hard work starts if 
you want more.

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-- Archie Warnock                     Internet:  warnock@stars.gsfc.nasa.gov
-- ST Systems Corp.                   SPAN:      STARS::WARNOCK
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