Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!rutgers!rochester!pt.cs.cmu.edu!nl.cs.cmu.edu!mlm
From: mlm@nl.cs.cmu.edu (Michael L. Mauldin)
Newsgroups: comp.graphics
Subject: Re: 24-bit RGB color to 8-bit color ?
Summary: Heckbert & Floyd-Steinberg
Message-ID: <4822@pt.cs.cmu.edu>
Date: 26 Apr 89 03:36:33 GMT
References: <538@rna.UUCP> <735@rocksanne.UUCP>
Organization: Carnegie-Mellon University, CS/RI
Lines: 32

In article <735@rocksanne.UUCP>, kirby@bozo.wbst128.xerox.com (Mike Kirby (co-op)) writes:
> >   Does anyone have a program to take an image with 24-bit color info
> >and build an 8-bit color map that is "good" (find the 256 color map entries
> >that produce the least error) ?

> Something like a 24-8 floyd-steinberg error diffusion algorithm,
> or some other method of dithering or error diffusion would probably
> have much better results then a histogram derived colormap.  

The FBM package has an implementation of Heckbert's median cut
algorithm to choose colors and Floyd-Steinberg to dither.  The routine
is called fbquant, and the package is available from:

    Host:	nl.cs.cmu.edu (128.2.222.56)
    User:	anonymous
    Password:	name@site
    Directory:	/usr/mlm/ftp/
    Filename:	fbm.tar.Z
    Transfer:	'image'

    Note: you must 'cd' to /usr/mlm/ftp directly, you cannot access
    either /usr, or /usr/mlm alone.  Don't forget to specify 'image'
    format transfer.

The only 24bit formats it can read are Sun rasterfiles and Amiga Digi-view
"raw" files.  It can output a variety of formats including Sun, GIF,
and Amiga IFF.  The software is in the queue for comp.sources.unix, so
if you're not in a hurry it'll get to you on its own.

Michael L. Mauldin (Fuzzy)		School of Computer Science
ARPA: Michael.Mauldin@NL.CS.CMU.EDU	Carnegie Mellon University
Phone: (412) 268-3065			Pittsburgh, PA  15213-3890
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