[Openicc] Introduction / Gutenprint

[Gerhard Fuernkranz]

Robert L Krawitz schrieb:

>The harder problem is when your application simply
>generates Postscript and hands it off to CUPS (or
>LPRng, or whatever).
>
Actually I see one more problem in this context:

So far, only color management in the gimp-print driver has been 
considered. But if the driver performs color management, how does it 
cooperate with the PostScript color management?

PostScript level 2 and 3 define color management functionality, and any 
PostScript document may legally use it, for instance CIE-based color 
spaces, which are of course expected to be rendered correctly by a 
"PostScript level 3 printer" (i.e. ghostscript + driver + printer in our 
case). IMO particularly color managed applications which produce 
PostScript or PDF output may likely use these particular PostScript or 
PDF features.

Ghostscript does support the PostScript level 2+3 color management 
features (color space arrays, color rendering dictionaries, CIE-based 
color spaces, remapping of device color spaces to CIE-based color 
spaces, ...), but in order that ghostscript's PS color management works 
as specified in the PLRM, my understanding is that all color 
transformations need to be carried out _by ghostscript_ (and not in the 
driver), and gs eventually sends only the final DeviceCMYK values (or 
whatever ProcessColorModel is used) to the driver. Of course this also 
requires, that a CRD for the printer (that's more or less the PostScript 
equivalent of the printer's ICC profile), and maybe also transfer 
functions (for device linearization), need to be passed (as PostScript 
program) to ghostscript, together with the document being printed.

Btw, though ghostscript's CIE-based color rendering basically works 
pretty well, I'm still not fully convinced with the quality. The color 
rendering quality of gs 8.xx seems to be _much_ better than gs 7.xx, but 
applying ICC profiles directly to an image (with LCMS or Argyll) and 
sending the resulting DeviceCMYK image as PS file to ghostscript gives 
IMO still better results, than ghostscript't CIE-based color 
transformations.

Regards,
Gerhard