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From: rcd@ico.isc.com (Dick Dunn)
Newsgroups: comp.lang.postscript
Subject: Re: Negative needed
Summary: use settransfer
Message-ID: <1991Apr15.191334.24390@ico.isc.com>
Date: 15 Apr 91 19:13:34 GMT
References: <1991Apr11.124626.12325@pbs.org> <1947@chinacat.Unicom.COM>
Organization: Interactive Systems Corporation, Boulder, CO
Lines: 23

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...
[more on how to find/change uses of setgray]

A better way is to change the transfer function; that way you only have to
make one change and not worry about whatever "setgray" commands may exist.
(You're much less likely to find settransfer commands in a PostScript
file.)

In fact, there's an example in the "red book" (PS reference manual) - sec.
4.8 in the first edition, 6.3 in the second edition - which suggests
	{ 1 exch sub }
as a transfer function (give it to "settransfer") that gives you a
negative result.  Transfer functions have domain and range [0,1]; the
above procedure just flips the argument around.
-- 
Dick Dunn     rcd@ico.isc.com -or- ico!rcd       Boulder, CO   (303)449-2870
   ...While you were reading this, Motif grew by another kilobyte.