[cairo] Spot colors (and CMYK)

[Chris Murphy]

On Feb 17, 2010, at 9:30 AM, ecir hana wrote:
> Yes, I really want to control the CMYK, such API is the topic of this thread.
> 
> If I say CMYK(40, 30, 30, 100) I want CMYK(40, 30, 30, 100). I bet you
> understand what I'm talking about - it's the same as reading Quicktime
> and writing it back as Quicktime, as you wrote above - going from CMYK
> to sRGB and back to CMYK makes no sense.
> 
> Again, the real question is, how do you supply CMYK image to Cairo and
> first, show it on the screen and second, export it to PDF with the
> same set of graphic operators?

Seems to me if there is no compositing being performed, any CMYK object (tagged or untagged) could simply be passed through, along with color space metadata. However, if any compositing is being done between objects of different spaces, they do need to be normalized first to a common color space. Ignoring the color space of either object is a kind of data loss.

This is a PDF/X-3/4/5 vs PDF/X-1a kind of workflow. One is early binding (everything is CMYK, nothing is to be repurposed/converted except for soft and hard proofing purposes, where you DO NOT WANT 40,30,30,100), that's PDF/X-1a. And the other is late binding which means predominantly ICCBased objects, all of which are converted when you get to the output stage and have a better idea where the job will print.

Saying you want specific CMYK values means you know exactly what printing behavior you're targeting including the media and ink set. CMYK values are control signals. They only translate into color when the device is known/defined.


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