[cairo] Spot colors (and CMYK)

[Francois Robert]

Bill Spitzak wrote : 

> Are you saying Cairo should blend in the source color space? 
> What happens if I print two things in different color spaces 
> atop each other? 
> What if I then print another image atop that? Please answer 
> with a LITERAL description of the resulting match and exactly 
> what ends up in each of the channels of the device and how 
> exactly this works with a finite number of result channels.

A stated goal of Cairo (at least at the beginning) was to replicate the
PDF 1.4 blending model. Reading the PDF specs should answer all those
questions. In particular, I repeat what I wrote earlier : A transparency
group can *explicitely* define a blending colorspaces. Some default does
exist of course, but the point is that the blending space *can* be
user-defined.
In the PDF specs, there is also a section dedicate to spot colors and
transparency.