[argyllcms] Re: FWA overcompensation bug in spec2cie

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 15 Jul 2010 21:44:54 +1000

Alexey Gribunin wrote:
Hello Graeme!

You aren't doing the same thing though. The CIE values from the first
are with a D50_0.0.sp illumination (UV and some blue filtered out). For
the second, you are applying a D50 illumination, and the extra blue
in it results in different values. If you do a:
spec2cie.exe -i ref/D50_0.0.sp -o 1931_2 -n Test_UVCut.ti3 Test_UVCut_CIE.ti3

Yes, it's clear. If I will do it, I will get Lab values compensated two times.

That's not the case. There are two separate things going on. One is
changing the effective spectral reflectance values to allow for the
different UV level. The other is the combining of the spectral reflectances
with an illuminant to compute the XYZ tri-stimulus. The spectral
values out of spec2cie -f have the first done to them, while
the XYZ values have both, the illuminant being D50_0.0.sp.
When you do the second spec2cie you need to use the same
illuminant to get the same result.

But I need it compensated only once, in one step like this:
spec2cie.exe -i ref/D50_0.0.sp -f -o 1931_2 Test.ti3 Test_UVCut.ti3

It is only being modelled once with this command.

Graeme Gill.

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