[cairo] Spot colors (and CMYK)

[Chris Murphy]

On Feb 17, 2010, at 12:31 PM, Bill Spitzak wrote:

> 
> 
> Chris Murphy wrote:
>>> re: color profiles convert to 3D
>> 
>> True for device class profiles, i.e. display device, input device, output device (there are commonalities, but these are different profile classes).
>> There is yet another profile class that can be used to preserve aspects of 4D color spaces (or more channels even). That is the DeviceLink class. It does not make use of a PCS, so there isn't, in effect, a conversion to LAB or XYZ. So such profiles can be built to do things like preserving 100%K only (e.g. for black text).
> 
> However this sounds like the proposed "spot color" api. Ie "use exactly this ink on the output device, and here is a portable simulation in case you are not the specific output device".

DeviceLink profiles are not used for spot colors, or spot to process conversion. That's the domain of a different class of ICC profile, the Named-Color profile. Two different profile classes with different structures.

One does not need to use the ICC specified Name-Color profile format to do this, you can use any kind of lookup, that correlates named colors to XYZ or LAB values. And then use an output device profile to convert from XYZ/LAB to device space. There are advantages to being a little smarter about this than just simple conversions for hard proofing, but this is best handled in software that is geared for hard proofing. For soft proofing, it's not as big of a discrepancy to just do a simple XYZ/LAB to DisplayRGB conversion, if the display behavior actually correlates to the display profile being used.


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