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

[Klaus Karcher]

>> Craig Ringer wrote:
>>> I increasingly think that user interfaces need to offer _five_ rendering
>>> intents, with a strong emphasis placed on the first two shown, eg:
>>>
>>> Perceptual
>>> Relative Colorimetric with BPC
>>> -- Rarely Needed --
>>> Relative Colorimetric without BPC
>>> Absolute Colorimetric
>>> Saturation

> Alastair M. Robinson wrote:
>> Agreed, once again.  I already use five-intents rather than
>> four-intents-and-a-checkbox in PhotoPrint, and may well take up your
>> idea of emphasising Perceptual and RC/BPC.
>

Hal V. Engel wrote:
> I also agree since having a BPC check box implies that BPC will do something 
> with intents other than relative colorimetric when this is not the case.  
> Many users find this confusing.
> 

The concept of five rendering intents instead of separate BPC checkbox 
meets my perfect approval.

>>> The "Use black point compensation" option would then be removed
>>> entirely.

:-)

>>> (Or are there circumstances when it does make sense for other
>>> intents?)

I don't think so.

>> As far as I know the BPC flag is simply ignored with intents other than
>> Relative Colorimetric - at least with lcms.

it looks like:

icctrans -t0 -i ISOcoated_v2_eci.icc -o ISOnewspaper26v4.icc
100 100 0 100 -> C=59.19 M=45.28 Y=40.54 K=94.91

icctrans -t0 -i -b ISOcoated_v2_eci.icc -o ISOnewspaper26v4.icc
100 100 0 100 -> C=59.19 M=45.28 Y=40.54 K=94.91

Adobe Applications behave differently unfortunately, e.g. Photoshop CS2:

perc. without BPC: 59.2 45.1 40.4 94.9
perc. with    BPC: 54.9 41.2 36.9 89.8

Even worse: In InDesign, you can choose a separate Rendering Intent for 
every image, but there is only one BPC setting for the whole document :(

Klaus