Hi, I'm writing because it's actually quite hard to do it with Argyll and I have a wishlist for spec2cie. Tindemans ACR calibrator script (http://www.21stcenturyshoebox.com/downloads/ACR-Calibrator-L-v31.jsx) stores the ColorChecker reference values in ProphotoRGB. It stores values for three illuminants: A, D50, D65. If you convert spectral readings w/ spec2cie spec2cie -i illuminant.sp -o 1931_2 -n measurement.ti3 converted.ti3 then you have to do CAT from the source illuminant (illuminant.sp) to the destination illuminants (A, D50, D65) and also convert the XYZ/Lab values to ProphotoRGB. This is a *VERY* long work to do manually with the help of the Bruce calculator (http://www.brucelindbloom.com/). Also, the Bruce calculator only supports few illuminants, so you have to implement your own CAT into an excel sheet if you want to use your custom illuminant. So I suggest to add two more parameters to spec2cie: --cat and --rgb The first will do chromatic adaptation transform to the given illuminant, the second will convert the chromatic adapted values to the selected profile. So the command will be: spec2cie -i myilluminant.sp -o 1931_2 -n --cat [A|D50|D65] --rgb Prophoto.icm colorchecker.ti3 copypasteme.ti3 Cheers, Darkbasic