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From: hawley@adobe.COM (Steve Hawley)
Newsgroups: comp.graphics
Subject: Re: What's the best colormap for a 24 bit color image?
Message-ID: <5738@adobe.UUCP>
Date: 17 Aug 90 20:49:22 GMT
References: <15019@samsung.samsung.com>
Reply-To: hawley@adobe.UUCP (Steve Hawley)
Organization: Adobe Systems Incorporated, Mountain View
Lines: 31

In article <15019@samsung.samsung.com> mdich@schizo.samsung.com (Mike Dichiappari) writes:
>What is a good algorithm or method for determining the best (or a
>very good) colormap given a 24 bit image?  I'd like the algorithm
>to work for various sized colormaps (although 256 will be most
>commonly used).

See the answers to frequently asked questions in the newsgroup comp.graphics.
I believe a very  workable solution has been done by Paul Heckbert that
quantizes 24 bit color down to 8 bit color.


>Is such an algorithm built into 32 bit Quickdraw?  Are there any
>standard algorithms for doing this?  How about any technical 
>references?

I understand that 32-Bit Quickdraw has an option to do color dithering.  If
you go this route, your code will not work the same on both Macintosh and Suns
and you are limiting yourself to Macs that support or can support 32 bit
Quickdraw.

If you want portability across platforms, use a reasonable color quantizing
algorithm and perhaps sweat out the details of doing color Floyd-Steinberg
dithering or color ordered dithering.  A good general reference for dithering
is "Digital Halftoning" by Robert Ulichney published by MIT press.  I don't
recall if it has anything about color, though.

Steve Hawley
hawley@adobe.com
-- 
"I can always telephone, but I can't tell it much."
	-Roy Blount