[cairo] Spot colors (and CMYK)

Kai-Uwe Behrmann ku.b at gmx.de
Wed Feb 17 23:36:44 PST 2010

Am 17.02.10, 22:56 +0100 schrieb ecir hana:
> On Wed, Feb 17, 2010 at 9:26 PM, Bill Spitzak <spitzak at gmail.com> wrote:
>> Kai-Uwe Behrmann wrote:
>>> By deploying a sRGB float model the colour conversion from input space
>>> to blending space, in this case a fixed sRGB, is just moved outside
>>> cairo. The cost for that is no support of deviceN and alternative
>>> blending spaces. I would never ever think of blending each colour space
>>> with each other. If thats what you are afraid of, I can only agree. That
>>> would not be supportable in cairo. But it is not what was suggested.
>> Okay that is good to know.
> Maybe I misread here but "I would never ever think of blending each
> colour space with each other." is exactly what is needed. You create

Yes, it is needed. But not directly by blending RGB over Cmyk. I would not 
know how to directly do this.
The app must decide, which space is prefered for blending and then after 
colour conversion of on element the blending can be done in one common 
color space.

> RGB image surface so you can bit blit it on the screen. And you paint
> a CMYK picture over it.
> If you are saying I first have to convert my CMYK to sRGB so I can
> compose it over my image surface, how do I send that CMYK to PDF?

I would choose Cmyk as blending space and convert Rgb to that and put all 
the resulting Cmyk with the ICC profile into PDF.
For screen simulation Cmyk would have to be converted to monitor RGB.

kind regards
Kai-Uwe Behrmann
developing for colour management 
www.behrmann.name + www.oyranos.org

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