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From: ph@nyit.UUCP (Paul Heckbert)
Newsgroups: net.graphics
Subject: Re: Allocation of color map
Message-ID: <135@nyit.UUCP>
Date: Mon, 24-Jun-85 21:12:03 EDT
Article-I.D.: nyit.135
Posted: Mon Jun 24 21:12:03 1985
Date-Received: Thu, 27-Jun-85 08:21:16 EDT
References: <12800001@umn-cs.UUCP>
Organization: NYIT Computer Graphics Lab., Old Westbury, N.Y.
Lines: 37

> ... The problem is allocating the color
> lookup map (8 bits deep) properly to match whatever distribution of colors
> result from any single run [of my ray tracer] ...

Thanks to Kurt Papke and Leo Hourvitz for recommending my SIG'82 paper.

It sounds like Scott basically has two choices:
   (a) Generate and store the picture in full color (24 bits)
       and then quantize down to 8 bits as a post-process, by looking
       at the statistical distribution of the picture's colors.
   (b) Pick a colormap a priori and quantize all pictures to it.
       3 bits red, 3 bits green, 2 bits blue works well.

The first method is more difficult but can yield superior results.
The latter method can be done on the fly, so that the picture is
written to the frame buffer as it is computed, and it also has the
advantage that all of the pictures will use the same colormap,
which makes compositing easier.  In either case I recommend dithering.

[ADVERTISEMENT]  If you're into other 8-bit frame buffer tricks,
perhaps you'd be interested in another paper I wrote:

	Techniques for Real-Time Frame Buffer Animation
	FX'84, London, Oct. 1984

I'll mail you a copy if you send your USmail address.

			Paul Heckbert
			NYIT Computer Graphics Lab
			ucbvax!decvax!philabs!sbcs!nyit!ph
				      allegra!sbcs!nyit!ph

(Sorry about the delay on this response; we've had some network problems
here for the past few weeks)
-- 
ucbvax!decvax!philabs!sbcs!nyit!ph		Paul Heckbert
              allegra!sbcs!nyit!ph		NYIT Computer Graphics Lab