[lug] Re: GIMP: is CMYK imprtant for monochrome work (fwd)

[Anders Knudsen]

At 10:15 AM 7/18/00 -0600, Michael wrote after Wayde:
>It's mostly due to the issues related to color matching with respect to
>video card and monitor settings *and* the conversion to CMYK.  This was
>recently mentioned on the Gimp Developer mailing list.  When people work
>with CMYK they are looking at print output specifics, so they expect the
>display to show exactly what they're getting in print, but that requires
>proprietary color matching (pantone, for example) that can be adjusted
>visually for monitor and printer differences.
>
>The algorithm for converting from RGB to CMYK is not difficult, but thats
>only a small part of the real problem.

Yes. The conversion of RGB to CMYK is a very simple formula, however, as 
Michael stated, it's the infinitesimal intricacies of "color matching" 
which foul up this simple formula.
Were you just to take an RGB image and then use the simple formula to 
convert it to CMYK, your results on the printed page (off a printing press) 
would be unacceptable. Many folks have spent a lifetime on just doing 
"color science" to perfect what are now in the industry called "color 
profiles", where you are profiling the color gamuts of the source image, 
your monitor and the target device (ink on paper.)
Photoshop, only now since v5.0, has an acceptable CMYK conversion engine. 
Prior versions of Photoshop did not always do a very good job with the CMYK 
conversions. To get the best quality CMYK results from Photoshop, one would 
use third party color profiles (ICC compliant) from companies like Kodak, 
AGFA, Efi, etc., rather than the built in algorithms -- most of the good 
profiles are an added cost.
Good color engines don't even convert from RGB to CMYK directly, rather, 
they will use an intermediate step and may first go from RGB to Lab, and 
then go to CMYK -- the whole time being tweaked by the "selected" profiles. 
There are many more details that have to be considered, but needless to 
say, "adding" RGB to CMYK in GIMP would not be a trivial task, but it sure 
would be cool!

-Anders (i used to do color in my previous career ;-)