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From: rjk@sequent.UUCP (Robert Kelley)
Newsgroups: comp.graphics
Subject: Looking for route from 24-bit rgb to postscript separations
Summary: convert 24-bit rgb to 4 postscript separations
Keywords: conversion dithering postscript
Message-ID: <25612@sequent.UUCP>
Date: 30 Nov 89 19:46:41 GMT
Reply-To: rjk@sequent.UUCP (Robert Kelley)
Followup-To: comp.graphics
Organization: Sequent Computer Systems, Inc
Lines: 20

I've been generating nice fractal images in 24-bit RGB
that I would like to dither to 8 colors:

	Black, Cyan, Magenta, Yellow, Red, Green, Blue, White

I want to generate 4 separate device-resolution postscript files,
one for each of CMYK, for subtractive printing.

I also want to generate 3 separate device-resolution postscript files,
one for each of RGB, for additive printing on a black background.

Earlier experiments tend to favor Floyd-Steinberg dithering with blue
noise (as described in Ulichney's excellent book, _Digital_Halftoning_)
for this kind of image.

The source format is my choice, since I need to write a program to generate
the original images.

Can anyone suggest an easy solution to this problem, perhaps using pbm or
other freely-redistributable software?


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