[Scribus] OT simulating CMYK printing in RGB space

Hal V. Engel hvengel
Sat Apr 1 22:01:44 CEST 2006

On Saturday 01 April 2006 10:41 am, you wrote:
> 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,


Seems like you are using a strange approach.  Do you have a profile for the 
device you want to proof?  Do you have a profile for the CMYK image?  Do you 
have a profile for your display?  If you don't then there is no way to get an 
accurate proof.   If you do then the normal approach is to use a CMS to do 
the work.   This is easy to do, quick and accurate.

You can use LCMS to create a proofing transform something along the lines of 
(image CMYK profile) --> (output device CMYK profile) --> (display RGB 
profile).  The end result is a transform that converts the image from it's 
original CMYK color space into the display color space with an intermeadate 
step that will gives you the limited gamut of your intended output device.  
You can view the converted image on your display and it will simulate the 
result you will get from your intended output device.   Pretty standard stuff 
and not hard to do if you have the needed profiles.  LCMS has command line 
utilities that will let you do this in a few minutes. 

Better yet I believe that Scribus will also do this same thing but with less 
effort on your part.  All you need are the correct profiles.


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