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From: brp@howitt.dog.oz.au (Bruce Perkins)
Newsgroups: comp.lang.postscript
Subject: Re: Color PS->PS
Summary: Solution for ...
Message-ID: <150@howitt.dog.oz.au>
Date: 24 Jan 91 03:49:32 GMT
References: <60410001@hpopd.pwd.hp.com>
Organization: CSIRO Division of Geomechanics Australia
Lines: 51

In article <60410001@hpopd.pwd.hp.com>, bijal@hpopd.pwd.hp.com (Bijal Shah) writes:
> 
> 
> 	Is there any program available that will convert a color PS document
> 	to a grey scales or ordinary PS document suitable for a Laserwriter?
> 


You should find that a color postscript file will print on a standard
PS printer such as a Laserwriter. There is a builtin algorithm for
mapping the colors to grayscales, but I have yet to see how you can
control that mapping (it may not be possible at all!). However.....,

One of the great things about postscript is you can redefine commands.

You could simply convert all set color commands to "black" by inserting 
the following line before any setrgbcolor commands:-

/setrgbcolor {pop pop pop 0 setgray} def

Alternatively you might want to use the RGB components (the top 3
items on the stack) in some algorithm to come up with a grayscale.
An algorithm I have seen is:- 0.3*Red + 0.59*Green + 0.11*Blue

Implementing this could be done by:-

/setrgbcolor {0.11 mul exch 0.59 mul add exch 0.3 mul add setgray} def

I have found occasion where I have needed to do the reverse of what
you want. The code I use for that is similar to:-

%! Pseudocolor for postscript grayscales
%% This postscript code assigns a "pseudo-colormap" to a
%% grayscale postcript file. The entries defined for the
%% postscript array "cmap" can be modified and/or extended 
%% as required. In this example a postscript "0 setgray"
%% is mapped to "0 0 0 setrgbcolor" and "1 setgray" is
%% mapped to "1 1 1 setrgbcolor" 
/cmap[
[0 0 0] [1 0 0] [1 1 0] [0 1 0] [0 0 1] [0 1 1] [1 1 1]
] def cmap length 1 sub /cmapsize exch def
/setgray {cmapsize mul cvi cmap exch get aload pop setrgbcolor} bind def


Hope this helps

Bruce Perkins
CSIRO Division of Geomechanics
Melbourne, Australia

brp@dogmelb.oz