[cairo] Spot colors (and CMYK)

Kai-Uwe Behrmann ku.b at gmx.de
Tue Feb 16 00:09:35 PST 2010

Am 16.02.10, 18:19 +1100 schrieb Andrew Cowie:
> On Tue, 2010-02-16 at 06:42 +0100, Kai-Uwe Behrmann wrote:
>> End to end colour management has a price. If well designed it can be
>> supported. The cost rises, when major components are colour management
>> unaware. Cairo comes with convenient features but currently completely
>> excluding colour management without a adequate chance to circumvent that
>> situation. Its like the toy API for fonts. Nothing serious.
> By analogy, we have Pango as the intimately-tuned and
> tightly-coupled-to-Cairo text rendering library which we all use. Adrian
> has suggested he wants the mooted PDF drawing API to live in a similar
> library. Can't wait.

That needs eigther garanties from cairo to support a stable backend API, 
practical a plug-in system. Or the code must be maintained by someone 
according to cairos changes.

> Are you also suggesting that we need to move the colour managment stuff
> into such a dedicated companion library? Is that the solution?

It would make life much easier to switch to whatever CMS a user decides.
This might be WCS, ColorSync or what someone decides else.

> [That seems at odds with the "tight drawing API, powerful backends"
> notion, but I'm all in favour of Cairo getting whatever it needs so that
> things are in general a) easier and b) more likely to be correct out of
> the box for applications developers]

Not necessarily. As long as backends know how to use the hooked in 
functionality that could work.
Cairo can then eigther call dummies and all remains as is, assuming sRGB 
as input, or uses the hocked in CM API. Tagging of the elements or at 
least the cairo context would be still necessary to pass that through as 
meta data to backends. Backends can then use that data to embedd profiles 
or request the magically right colour for a given element without mutch 
decissions inside cairos code. The cairoCM wrapper could then support each 
backend individually.

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

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