[cairo] Spot colors (and CMYK)

Chris Murphy lists at colorremedies.com
Wed Feb 24 00:29:18 PST 2010

On Feb 24, 2010, at 1:00 AM, Francois Robert wrote:

> 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.

What are the chances of looking to Ghostscript for PDF blending support? They've already done this as far as I know. All of the blending modes supported in Photoshop, PSD, then placed into InDesign and output to PDF with live transparency are blended correctly using Ghostscript 8.64. So instead of reinventing this wheel, it might be useful to tap into Ghostscript if that's possible (I don't know anything about licensing issues). 

Chris Murphy
Color Remedies (TM)
New York, NY
Co-author "Real World Color Management, 2nd Ed"

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