[argyllcms] Issue reading illuminant spectrum

  • From: Niccolò Belli <darkbasic4@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 05 Nov 2010 00:06:15 +0100

Hi,
after reading the patches of my X-Rite ColorChecker with the Colormunki
Photo I decided to try converting the spectral informations using a
custom illuminant. Light source is a tungsten lamp, so something similar
to standard C illuminant.

I read the patches from the ColorChecker 24:
chartread -p -H ColorChecker

I created a custom illuminant file:
spotread -a -s -H
then, after calibration, I pressed the instrument's button and then 's'

I converted the ColorChecker spectral informations to XYZ/Lab using C
custom illuminant:
spec2cie -i customC.sp -o 1931_2 -n ColorChecker.ti3 customC.ti3

I converted the ColorChecker spectral informations to XYZ/Lab using C
standard illuminant for comparison:
spec2cie -i C -o 1931_2 -n ColorChecker.ti3 standardC.ti3

The difference is VERY, *VERY* big. Let's see a comparative screenshot:
http://darkbasic.homelinux.com/images/custom-vs-standard-C-illuminant.png

Here are the spectral readings:
http://darkbasic.homelinux.com/images/illuminant_spectrum.zip

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