[Openicc] seeking for advice on rendering intent and black point compensation

[Kai-Uwe Behrmann]

Hello,

Am 03.10.07, 12:47 +0200 schrieb Sven Neumann:

> When opening an image file that has a color profile embedded, GIMP
> offers to convert from the embedded profile to the configured RGB
> workspace profile (which will be sRGB for most users). This conversion
> currently happens with hardcoded parameters for rendering intent
> (perceptual) and black point compensation (off). My questions are:
> 
> (1) Are these good default values or would you advice to change them?

For an simplistic sRGB workflow editing all in preceptual sRGB might be 
considerable. 

Of course, to adapt later to a standard meet by other applications 
would help in having a more consistent behaviour across those 
applications. 

Further most settings need to be the same among applications. But this 
state is not yet reached. The profile in X was indeed a first step in this 
direction.

> (2) The rendering intent used for the display color correction can be
> configured in the Preferences dialog. Would it make sense to reuse this
> setting for the conversion when loading an image? Doing so would make
> sure that, with display color correction enabled, the image would look
> the same whether it is converted on load or not. I am currently
> inclinded to follow this argumentation and to change the code
> accordingly.

Coupling the display and conversion rendering intent seems logical, and is 
in fact deployed in other applications, namely CinePaint, Krita(?) ...

Even though it is possible to convert with pleasing appearance 
(perceptual) from a device colour space into a editing colour space (in 
your case sRGB) but want to look at the image with absolute colorimetric. 
But that is not so often the case, and may cause more users headache than 
wanted.

> (3) Should the black point compensation setting be configurable somehow?
> Currently we are using "off" all over the place and don't give the user
> a chance to change that. Should we enable BPC for printer simulation? Do
> we need to add configuration options for this? Would we need different
> settings for display color correction and soft-proofing?

BPC is used in conjunction with relative colorimetric only. For printer 
simulation, allowing different settings seems appropriate.
Be warned about using relative colorimetric without BPC. Your users will 
seldom expect such results.

For a, not even full blown, colour mangagment configuration dialog see:
http://www.oyranos.org/wiki/index.php?title=Oyranos_Configuration_Dialog
The various options are described in a minimalistic fashion. You'd be 
interessted in the Behaviour tab options.

> In advance, thanks for sharing your expertise.

Hope it helps.

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