Re: Change color of EPS file.

From: Henning Hraban Ramm <hraban@fiee.net>
To: mailing list for ConTeXt users <ntg-context@ntg.nl>
Subject: Re: Change color of EPS file.
Date: Sun, 16 Sep 2012 10:03:23 +0200	[thread overview]
Message-ID: <CAPm68ZiXeKmDJt2dzA03ycSmZPEEJM+z2PXXD+feea+r-VTZ4Q@mail.gmail.com> (raw)
In-Reply-To: <CAFP+xFL2VZg2N=9og4Q7p7uXVPCZ_8b+ynggtcjPwR9=EMxKxA@mail.gmail.com>

2012/9/15 Troy Henderson <thenders@gmail.com>:
> Utilities are available in abundance which can transform raster graphics
> from color to grayscale, but until I created this yesterday, I have never
> seen a utility that keeps the graphic in vector format (i.e., never
> rasterizes it throughout the conversion) and converts it from color to
> grayscale.  Until I read this thread, I guess I thought I was the only one
> that desired such a tool.  I'm glad to see that at least I'm not alone.

Oh, there are, but I know only commercial (e.g. OneVision Asura) or
in-house solutions (like what I "managed" at a newspaper several years
ago).
The simple (or simplistic) rgbcolor patch doesn't work with
complicated EPS, of course. But then you'd need to know the structure
of your EPS. It's hard to get that right for arbitrary EPS. And there
aren't that many able PostScript programmers left.
E.g. at that newspaper we were able to switch spot colors just before
plate exposition; the trick was to use a generic spot color name
throughout the workflow and to change its definition in the completed
page EPS. (At that time "our" printing press was too small to print
all pages in full color.)

Since PostScript is a full programming language, most PS generators
use shortcuts (macros/functions) that wrap the originally simple
commands, so you often can't track down where the structure hides that
you'd like to change. Best solution is often to do a full "expansion"
with a PS interpreter and write a new, better readable, but mostly
much bigger code. pstoedit is your friend for that – e.g. Hans did
some nice tricks with EPS pictures converted to MetaPost.

I once experimented a bit with changing colors of embedded bitmap
images – it's rather easy to do, but never looks right without a deep
understanding of color management and its strange implementation in
PostScript...

Greetlings, Hraban
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