[argyllcms] Re: Recent Monaco IT8 Reference Files have incorrect XYZ values
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 31 May 2021 11:34:34 +1000
JP wrote:
I wanted to call out what I believe to be an error in X-Rite Monaco IT8
reference files
(https://www.xrite.com/service-support/downloads/m/monaco-it8-reference-files)
that would affect
folks generating input profiles with ArgyllCMS, specifically when using
scanin.
The Lab values look about right; that's the color white, alright. However
when I plug the XYZ
values here into http://www.brucelindbloom.com/ColorCalculator.html ;(with
"Scale XYZ" checked, Ref.
White of D50 and all the other settings default), the corresponding Lab
values are [91.57 22.18
43.29]! Way off. This is a peach/yellow-ish color; in (scaled) ProPhoto RGB
it's [251.0 213.6 144.4].
Hi,
thanks for the heads up. The XYZ values are the primary measurement
values, with L*a*b*
being derivatives, and (given the choice) the less reliable of the two since
there is an
(most often) undocumented dependence on the white point used in the conversion
to L*a*b*.
By convention graphic arts tri-stimulus measurements should be for a D50
illuminant, but
again it's much better when this is stated, rather than being assumed.
X-Rite have a big "Contact Us" button on the download page, so probably best if
you contact them and ask them what's going on with their measurement values...
Cheers,
Graeme Gill.
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