Re: Getting the primaries of a profile
Re: Getting the primaries of a profile
- Subject: Re: Getting the primaries of a profile
- From: Graeme Gill <email@hidden>
- Date: Sun, 21 Oct 2018 22:47:29 +1100
Adriaan van Os wrote:
As a side bar, I wonder about the Bradford and von Kries transforms.
Bradford is a Von Kries transform. A "Wrong" Von Kries transform is one
in XYZ space, rather than some sort of sharpened cone space.
I see them often
mentioned, but never the (allegedly more precise) revised CIECAM97s and CIECAM02 matrices
The subjective data that such transforms are based on, tend to be rather
"noisy",
so it's perfectly possible to arrive at different matrices that are optimal
for a given data set, but in practice may not have huge differences. So there
doesn't seem to be a great deal of consensus that any revised matrix is
a definite or obvious improvement over Bradford.
A CAM may well arrive at a slightly different sharpened cone space to
Bradford, simply because various parameters, including this matrix
get fitted to color appearance data sets that are not the same as those
used to derive the Bradford matrix.
[ Given that white point adaptation is primarily assumed to be a property
of the individual LMS cones adapting to light levels, the better fit to
experimental
data to sharpened cone spaces is rather interesting, since it doesn't seem to
be explainable at the retina level. ]
<https://en.wikipedia.org/wiki/LMS_color_space>.
Hmm. That entry seems to have a degree of misinformation. The transform
between XYZ and LMS space is not a chromatic transform, it is actually
a transform between two different primary sets, namely the LMS primaries and
XYZ primaries. In constrast, a chromatic transform represents a shift in white
point adaptation.
Graeme Gill.
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