This is more about philosophy than an actual answer to Stefan's question,
but maybe there it can inspire some more thinking.

This may be entirely my deficiency, but I am unclear on the general
usefulness of having a native CMYK implementation.  On one hand I
understand that there is a perceived value of working with the four
values, on the other hand I think we expose too much of the underlying
guts of the colour implemetation and gamuts to the poor user already.

Converting RGB to CMYK is algorithmic.  Here's the generalised algorithm:

  c = (255 - r) * Cr
        m = (255 - g) * Cg
        y = (255 - b) * Cb
        k = max(c, m, y) * Cy

Of course the interesting part about the algorithm are what to choose
for the values of Cr, Cg, Cb, and Ck, and *unless* you have the data on
the printer, the inks (lot numbers and even age), and paper, any values
you arbitrarily choose would likely be wrong.

A contribution here would be the development of a good colour abstraction
interface.  Let the user choose things like if the image is a COLOR image
or a Black and White image (GRAY), with or without transparency.  None of
this business of values like 255 (white in 8bit rgb).  Naturally there
will be people who want access to the underlying knobs and switches,
and that's okay. But we ought to at least put a cover over it.

I think CMYK ought to be a Save As option (as appropriate).


On Sun, Jun 08, 2003 at 11:13:33AM +0200, Stefan Klein wrote:
> Hi all,
> I am a computer science student looking for a final year project. I'd love
> to do something in the Open Source community and I am looking around where
> my help might be needed. Having a little interest in graphics design and
> prepress, I came across GIMP and CMYK support. The little research I've done
> gives me the impression that over the last couple of years it's regularly
> been asked for and it might be an important feature to get GIMP into the
> pre-press world.
> What I'd like to know is the following:
> 1. Is anybody actually working on this? There were hints now and then that
> people are thinking about it, but I didn't find anything definite, apart
> from an entry "Additional ColorModels" on the GEGL todo list
> ( that seems to point in that
> direction.
> 2. How important is this really? What I am talking about is native CMYK
> support, not just a conversion function. There was a thread on the
> developers-list in November 2001
> ([EMAIL PROTECTED]/msg01350.
> html) that gives the impression that it might not be all that important and
> that there might be cheaper workarounds (converting when saving, spot color
> channels). How important is a CMYK mode for people working in prepress?
> 3. Any guesses on the effort to implement this?
> I'd appreciate it if you could answer asap, since I have to hand in my
> project proposals very shortly.
> Thanks
> Stefan
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