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From: lee@leo (Bill Lee)
Newsgroups: comp.lang.postscript
Subject: Re: Negative needed
Message-ID: <1991Apr17.141806.20838@shell.shell.com>
Date: 17 Apr 91 14:18:06 GMT
References: <1991Apr11.124626.12325@pbs.org> <1947@chinacat.Unicom.COM>
Sender: usenet@shell.shell.com (USENET News System)
Organization: Shell Oil
Lines: 31

In article <1947@chinacat.Unicom.COM> woody@chinacat.Unicom.COM (Woody Baker @ Eagle Signal) writes:
>In article <1991Apr11.124626.12325@pbs.org>, rfutscher@pbs.org writes:
>> If I plot to a postscript file is there a way to edit the 
>> postscript file so that the drawing is printed as a negitive?
>> 
>Look through the file for the word setray.  It may be used in
>a procedure definition to make the file more compact.  IF it is, then
>examine it carefuly, and see what the incoming parameter is.  You can then
>modify the definition to complement the incoming paramater.
>
>Alternatly, you could search for every occurance of setgray or the
>re-defintion of it, and alter the parameter.
>
>Cheers'
>Woody


From the red book (rev.1) pg 82-83:

	"The transfer function may also be redefined to produce specific
	 effects. For example, the transfer function
		{1 exch sub}
	 will invert the output image; this is useful for producing
	 photographic negatives...."

This seems like a reasonable way to do the job: searching through a PS
file (that could be quite large) for all occurences of a setgray command
is not (IMHO) reasonable.

Bill Lee			lee@shell.com
Shell Oil Co.