[argyllcms] Re: FWA correction in XYZ space

[My apologies for being "off air" for the past week. I've been
away skiing (it's winter here in oz of course), and on returning have
found that the argyllcms mail server seems to be unable to send mail ...]

Gerhard Fuernkranz wrote:

Actually it looks like the effect of Argyll's FWA compensation can be also modelled pretty well in trichromatic space, either as XYZ_fwa_comp = f(XYZ), or as Lab_fwa_comp = f(Lab).

As function f, I have tested a linear relationsship, and 2nd order multivariate polynomials.

I was positively surprised by the good fit, both, in XYZ and CIELAB space. The errors were a bit lower in CIELAB space, thus I'm only considering the CIELAB results below.

The fact, that the CMYK results are as good as the RGB ones, though the transformation in CIELAB space cannot account for the 4th degree of freedom, gives some evidence, that the black generation has not a significant effect on FWA compensation. 

Thanks for sharing those results Gerhard. I guess it still leaves
the issue of how to derive the transform parameters from a minimal
set of measurements. It also tends to validate Gretag's approach,
which (I have been given the impression) is a XYZ_fwa_comp = f(XYZ) /
Lab_fwa_comp = f(Lab) type of approach.

cheers,

Graeme Gill.









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