[argyllcms] Re: Black-/White-Level Observer Dependency?

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 28 Sep 2010 10:35:54 +1000

Sam Berry wrote:
On 27 September 2010 14:18, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:
Good point. I will fix dispcal and spotread so that the color temperature
correctly takes into account a non-standard observer (I overlooked this
in adding an alternate observer).

I can't immediately think of any easy way to do it. I've had to calculate
D65 XYZ from scratch using the D65 spectrum. To generalise it would seem to
be an awful lot of work. Perhaps a warning that CCTs and VCTs are no longer
valid would suffice?

It was actually trivial to fix, because rather than use one of the approximation
formula for computing CCT, I do a numerical search for the temperature
at which the locus spectrum has minimum delta E to the measured XYZ.
(This is the definition of a CCT.) So all I had to do was change the code
so use the selected selected observer, rather than 1931 2 degree for computing
the XYZ of locus spectrum.

Graeme Gill.

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