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Re: Puzzle Solution and Compression



On Wed, 21 Oct 1998 14:32:53 -0400, mgutzwiller@lanvision.com wrote:
*>Tom et al.,
*>
*>A co-worker of mine actually got interested in compressing Mark III images
*>using a scheme similar to what Herb suggested.  By dropping the lower 4 bits
*>and using differences between pixel values he was able to get compression
*>ratios of about 3.5 to 1.  Dropping the lower 4 bits made no difference to
*>the Star program's results since the noise was on the order of 6 bits anyway
*>in my light polluted skies.  A similar approach might be usable for the Mark
*>IV.
*>
*>Note that using only the upper 12 bits would still give us a dynamic range
*>of 4096 to 1.
*>
*>Mike G.

Differences is not a bad scheme, that is what GIF formats do. If the
difference is only a few bits, you just use the deltas. If the difference
is large, you represent it directly and start the differences again.
It's a classic algorithm. And, since most of our image is dark, most of
the differences are small. Is there a FITS format that supports this?

Herb Johnson

Herbert R. Johnson              http://pluto.njcc.com/~hjohnson
hjohnson@pluto.njcc.com         voice 609-771-1503, New Jersey USA

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