[cairo] cmyk support in Inkscape/Cairo

[Ralph Giles]

On Fri, Sep 26, 2008 at 1:54 PM, Ian Britten <britten at caris.com> wrote:

> In some workflows, my users will *define* their colours in CMYK (ie In
> their own palette).  When they produce PS, they want those *exact*
> colours written out, not the result of a CMYK -> RGB -> CMYK conversion.
> As such, we maintain an abstract 'colour' class, with derived 'rgb',
> 'cmyk', etc, variants, which maintain the defined colours as they were
> originally specified.

If I understand correctly, this is what we call "device-dependent
colours", and it's not just avoiding CMYK->RGB->CMYK but CMYK->CMYK.
They're really a special case of named or 'spot' colours, and indeed
SVG Print defines them as such.

One way to handle this is to have clean pass-through, and assume the
application knows what it's doing for a particular device. That's a
bit old-fashioned, but is one way to structure the API. Another
approach is to always attach an ICC profile describing whatever space
(including non-CMYK, non-RGB named colours) the application is feeding
cairo, and then ensuring that colour conversion is a no-op if the
eventual output device uses the same profile. In the meantime, output
on other devices (e.g. for proofing) can be calibrated.

The latter is the more general API, but people used to pass through
may complain and wonder what to specify as an input colour space.

 -r