[argyllcms] Re: Monitor profiles and their (black point?) "readability"

Graeme Gill wrote:

Hmm. The black point tag in Argyll profiles simply reflects the behavior
of the device. The black point is still the same even if the tag
is missing.
You are right (once again ;-). I wrongly assumed that the TRCs of a matrix profile have to start with zero, but that's not the case: they can have an offset -- and this offset settles the black point. 


[...]

If they are using relative colorimetric intent, then the
black clipping behavior is exactly what they are requesting,
and if this behavior is objectionable, then I think they probably
have a bug. Perhaps they should use BPC.

I'm not sure why other profiles may not have this behavior, unless
the profile creation is somehow distorting the device characterization
to make it appear as if the black point is zero.
Exactly: they are cheating. (E.g. the GMB profile uses a single gamma value for each channel and therefore implicates a black point of zero) 


Since the ICC
profile is meant to reflect the measured behavior of the device,
I can't see that this is a valid approach.


acknowledged.


[...]
Kodak proposed to delete the mediaBlackPointTag and AFAIK this proposal is already approved by the ICC. Whether this decision makes sense is a different kettle of fish. 

No sense at all is the answer. The black point and white point
are pretty basic media information, and essential when doing
gamut mapping. A black point can be created from the A2B colorimetric
table, but it may be different to what the profile creator (who
is likely to take the most care about things and has more information
available) would create, and is also difficult to determine for CMYK
without ink limit information, which the ICC format lacks.


I agree.

Klaus

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