[colord] colord/cups printer profile rendering intent

[Pascal de Bruijn]

On Mon, Dec 17, 2012 at 11:36 AM, Richard Hughes <hughsient at gmail.com> wrote:
> On 11 December 2012 18:00, Pascal de Bruijn <pmjdebruijn at pcode.nl> wrote:
>> However I'm wondering if CUPS is aware of an image's source colorspace
>> (and if it can be, is this application dependant, in other words what
>> mechanism is used)?
>
> Yes. Ghostscript knows the source image colorspace (assuming it's
> tagged, else it assumes sRGB) and we pass in the output profile to use
> if it's been specified by the user.
>
> I'm no sure what rendering intent it used to be honest, although I
> assume perceptual. colord certainly doesn't tell ghostscript what to
> use.

Well the thing is, perceptual might be tricky...

Printer profiles are pre-calculated lookup table profiles. So there is
a separate lookup table per rendering intent. Where the saturation and
perceptual tables are calculated against a very particular source
colorspace*.

Only the colorimetric table is source colorspace indepedant, and thus
would be the safe choice

(When no particular source color space has been specified at profile
generation, the saturation/perceptual tables are typically just a copy
of the colorimetric table).

Regards,
Pascal de Bruijn

* If one takes a look at most profiles by paper vendors they are
typically calculated against AdobeRGB. While I'm aware those profiles
do not apply to Linux printer drivers anyhow, it is a good indicated
for what is considered common practice.