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From: lmiller@aerospace.aero.org (Lawrence H. Miller)
Newsgroups: comp.graphics
Subject: Re: Color Picking
Message-ID: <64144@aerospace.AERO.ORG>
Date: 28 Dec 89 17:07:17 GMT
References: <2241@cs-spool.calgary.UUCP>
Sender: news@aerospace.aero.org
Reply-To: lmiller@batcomputer.UUCP (Lawrence H. Miller)
Organization: The Aerospace Corporation, El Segundo, CA
Lines: 26

In article <2241@cs-spool.calgary.UUCP> datta@cs-sun-fsb.UUCP (Slarti) writes:
>
>What I would like to do is load in a color graphics format that is stored
>with 24 bit planes and display it on an 8 bit device.  This in itself is not
>difficult, but what I need is a method of choosing 256 colors that can best
>be used to represent the image, without dithering or the like.

Heckbert at Pixar has the best published algorithm on this.  However,
Paul Raveling at ISI (raveling@isi.edu) has been working on enhancements,
including fidelity criteria, that should be available in published form
soon.  Here is the Heckbert citation in refer format:

%A Paul Heckbert
%T Color Image Quantization for Frame Buffer Display
%J Computer Graphics
%D July, 1982
%V 16
%N 3
%P 297-307
%X Presents a method for selecting the N best colors to represent an image
digitized at M (M >> N) colors.  The methods presented are ``uniform
quantization'' and ``median cut.''  In uniform quantization, the N most
frequent colors are selected.  Median cut uses an adaptvie algorithm to
find the N ``best'' colors, and generally produces better results.  Typical
quantization levels are eight bits per pixel.  Dithering also increases the
quality of the final images.