[argyllcms] Re: perceptual black too light

Gerhard Fuernkranz wrote:
may I ask, how do you actually align the two white points (and how do you adapt all other source colors according to the WP shift)? Just a translation in Jab space? Chromatic adaptation? Rotation from src WP to dst WP in Jab space with center at [0,0,0]? Etc.? 

Currently it's a rotation in Jab space about 0,0,0. Usually the
shift is small, because Appearance space is close to being
white point relative.

So if I understand you correctly, the direction of the perceptual gray axis of the device being profiled is eventually determined by the wtpt..bkpt axis of the supplied _source_ profile (-> profile ... -S ...), while the lightness of the lower end of the device's gray axis is determined by the device's bkpt? What's actually the intention of this strategy? Looks like the created device profile inherits some of the source profile's personality (gray axis direction), but is this really desired in general? Shouldn't the device profile being created for a particular device rather represent the "native personality" of the device? 

From various feedback, I understood that this behaviour is not
desirable, in it's shifting of neutrals towards the hue of
the black point.

This is consistent with the findings from Sun Ju Park and
Mark D. fairchilds paper "Color Reproduction Using Black-Point
Adaptation" <http://www.cis.rit.edu/fairchild/PDFs/PRO16.pdf>,
which found that "Color reproduction based on being relative to
the black and white in a complete sense using chromatic and
lightness values is not preferred"

Subjectively, the algorithm I've adopted gives results that
are a closer visual match through the neutral axis,
than the previous one.

Graeme Gill.




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