[Openicc] Ghostscript CMS [was: PDF frustration]

[Gerhard Fuernkranz]

Kai-Uwe Behrmann wrote:
> Am 01.12.08, 11:47 +0100 schrieb Leonard Rosenthol:
>> On Dec 1, 2008, at 9:31 AM, Kai-Uwe Behrmann wrote:
>>>> The idea of the rendering intent is just to communicate to the CMS what is
>>>> requested for those colors in the document.  In PDF, you can set a 
>>>> rendering
>>>> intent.  The CMS will need to decide what it wants to do with that
>>>> information.  It may decide for perceptual intent for example that it will
>>>> do black point compensation.
>>> Bpc works only with relative colorimetric.
>> 	Are you sure about that?  In all of the discussions around BPC, I 
>> have never heard anyone say this before.
>
> http://www.adobe.com/devnet/photoshop/sdk/AdobeBPC.pdf section 6.2 says 
> that relative colorimetric is the primary target, as it has no mapping 
> from source black to destiniation black defined. Perceptual and saturation 
> should have this per definition. There is a advantage mentioned for the 
> case of malformed profiles.
> I agree that the relative colorimetric with BPC combination is not the 
> only allowed per this document, just from a practical point of view the 
> others combinations should play no role.

Kai-Uwe,

IMO, for perceptual/saturation intent a BP scaling may make sense in
conjunction with certain V2 profiles. The perceptual/saturation intent
of some (most?) V2 profiles seems to map "device black" to L*a*b* =
0,0,0 in the PCS, while some other V2 profiles seem to map "device
black" to L* > 0 [e.g. to the actual device BP, adapted to D50]. I'm not
sure, what's right or wrong, IMO in V2 it is not clearly defined.
Anyway, profiles which assume a different perceptual BP in the PCS do
not work well together w/o BPC when they are combined with
perceptual/saturation intent. When combining V4 profiles, this should
not be an issue any longer, since V4 has a well-defined perceptual BP in
the PCS, and the perceptual/saturation intent tables of V4 profiles are
expected to map device black to this well-defined perceptual BP in the PCS.

Best Regards,
Gerhard