[Scribus] OT simulating CMYK printing in RGB space

[Vic Mortelmans]

Hi,

slightly off-topic, since not about Scribus, but I posted because this 
list has a lot of knowledge about printing techniques (and I'm currently 
not involved in GIMP-lists).

I want to simulate the effect of multi-color offset printing. I have 
available a set of layers in the GIMP, each layer in one of the 
CMYK-colors. However, the GIMP doesn't have a layer mode that would show 
me how the image would look like when all these layers are printed on 
top of each other

What I tried out was to invert each of the layers, then use the 
'Addition' layer mode on each layer, and invert the result back again. 
Theoretically, this should be what I'm looking for, since each CMY-color 
is the invert of one of the RGB-colors (isn't it?). In practice, it 
looks like the right result...

I know the GIMP can decompose and compose CMYK-images, but I also want 
to simulate printing with other spot colors, which should work just the 
same.

To bring this topic in relation to Scribus, I'm considering creating a 
duotone print job with specific inks. A special processing of bitmaps 
can restore much of the original color information, but diversifying the 
image printed in both inks. Actually, my question is related to some 
experiments I'm conducting in that area, of which some information can 
be read here:

http://users.pandora.be/vicmortelmans/fts/duotone

Feedback welcome!

Please don't confront me with the fact that I overlooked some 
GIMP-feature that does all this out of the box :)

Groeten,

Vic