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List:       koffice-devel
Subject:    Re: The GIMP 2.0
From:       James Richard Tyrer <tyrerj () acm ! org>
Date:       2004-01-14 13:04:02
Message-ID: 40053E42.1010209 () acm ! org
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dirk.schoenberger@sz-online.de wrote:
>>>>From what I read in the core (gimp-devel 1.2), in the core RGB(A),
>>>grayscale and 8 bit indexed is supported. This can all be rendered in
>>>RGB(A).
>>
>>>Other colour models like CMYK are more complicated, because the
>>>conversion
>>>between CMYK and RGB is not quite simple.
>>
>>The conversion (for printing) is straightforward arithmetic to get CMY,
>>then you get K
>>which is MIN(C,M,Y) which is subtracted from all three.  But this just
>>renders that
>>additive color model.
> 
> 
> I had the impression that the whole problem what that RGB <-> CMYK
> conversion was not so straight forward than I thought.
> I think the whole conversion algorithm contains some linear factors
> (like K = 0.1C + .098M+.965Y or somesuch) instead of a pure minimum value.
> 
> But I don't have the exact formula handy, sorry.

There are fudge factors to deal with printers because the printers use real ink which is 
not perfect.  I think that GimpPrint does this.  But for the theoretical color model to 
convert back to RGB for screen display, I don't think that this applies.

Then there is the issue of color correction so that the screen image will exactly match 
the printed image, but that is also a different issue.

--
JRT

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