[Openicc] CUPS Color Management under Linux gets into distros

[Chris Murphy]

On Feb 21, 2011, at 12:13 PM, Alastair M. Robinson wrote:
> p
> 
>> I don't think this will do too much for us if you are rendering
>> everything to sRGB first and then to the final colorspace.
> 
> I disagree - if you're rendering to sRGB as an intermediate step (which, agreed, we don't really want to do - but it seems to be necessary for CMYK output profiles at present)

Why does it seem necessary? You're saying poppler would need to render to sRGB and then do a hand off to what to do the conversion to CMYK? If a handoff is needed because poppler can't do CMYK, why not hand it off right away and not have poppler to a conversion at all?


> If we have to use sRGB (or some wider-gamut RGB space) as an intermediate step, then we need to use Perceptual intent when converting that to the printer profile.

The issue is both the source space L* going to 0, compared to the destination space L* going to something more than zero, and the lack of Black Point Compensation to use with RelCol. When both of these are true, Perceptual rendering should be used.

> 
> This isn't an issue when the printer's profile is RGB - poppler can render directly to it - though my experiments last night suggest that's not working properly either as yet.

Even if a printer is described by an RGB output device profile, the L* will not go to 0 for any real device with a properly built profile. So the issue of intent is the same. Default rendering to print space needs to be either RelCol+BPC or Perceptual.

Chris Murphy