[Openicc] Ghostscript CMS [was: PDF frustration]

[Kai-Uwe Behrmann]

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.

>> As I recently looked over the
>> default CM settings, I remembered that many developers voted for five
>> rendering intents here some time ago:
>> http://lists.freedesktop.org/archives/openicc/2007q4/000963.html

>> I do not know if and how this, or bpc as a separate option, could make its
>> way into PDF.
>> 
>
> 	There is a proposal before the ISO 32000 committee to introduce BPC 
> into ISO 32000-2 (as an element of the graphic state, of course).  It will 
> most likely pass at the April meeting of the committee.
>
>
>> The native device colour spaces may not behave symetrical along the gray
>> axis. So gray should remain gray after applying a function to all channels
>> equaly.
>
> 	Maintaining values in the K channel (or any pure colourant, for that 
> matter) is also an issue being brought up at ISO 32000 for discussion.

Thanks for the sharing.


kind regards
Kai-Uwe Behrmann
-- 
developing for colour management 
www.behrmann.name + www.oyranos.org