[argyllcms] Re: profile -S -g

-------- Original-Nachricht --------
> Datum: Fri, 25 Apr 2008 02:13:16 +1000
> Von: Graeme Gill <graeme@xxxxxxxxxxxxx>

> > profile -S 'ISOcoated_v2_eci.icc' -cpp -dpp solventLFP
> > 
> > I get *heavy* clipping when using the perceptual intent.
> 
> That's most surprising. The source gamut is obtained from
> the colorimetric A2B table. It should not be subject to any
> gamut mapping, and should represent the true gamut of the device.

Graeme,

I guess the problem is the black point which you are assuming for the _PCS_.

V2 does not define a reference medium black point for the PCS, so we cannot 
rely on any standard here, but my impression is that most V2 profiles generally 
assume a PCS black point of L* = 0. I.e. the perceptual intent of most 
(non-Argyll) V2 profiles I've seen did map L* = 0 in the PCS to the actual 
media black, and L* = 100 in the PCS to the actual media white [and vice versa 
in the A2B0 table].

As long as e.g. sRGB or AdobeRGB are used for "-S", the assumed PCS black point 
of your profiles will be L* = 0 as well, and everything is fine. But if e.g. 
ISOcoated is selected as "-S" profile, then you assume the ISOcoated BP [which 
is > 0] as PCS black point, making your profile incompatible with other source 
profiles which assume a PCS black point of L* = 0 [and if you nevertheless 
combine them with perceptual intent, the result will be clipped colors].

Regards,
Gerhard



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