Re: Calculating from AbsCol to RelCol from L*a*b*?
Re: Calculating from AbsCol to RelCol from L*a*b*?
- Subject: Re: Calculating from AbsCol to RelCol from L*a*b*?
- From: Klaus Karcher <email@hidden>
- Date: Mon, 20 Apr 2009 09:32:16 +0200
Terence Wyse schrieb:
Hello all,
Anybody here know where I can find the formulae for calculating relative
colorimetry from absolute L*a*b* where the L*a*b* for paper white is
known? I know that it's not as simple as subtracting paper white L*a*b*
but I've searched and can't find the math used to come up with relative
colorimetric values.
see ICC spec Annex D.6 <http://color.org/ICC1v42_2006-05.pdf>:
The ICC profile format does not include an explicit transform for the
ICC-absolute colorimetric intent. On creating a profile only the
XYZmediawhite-relative values are stored in a profile, not XYZunder D50.
When using a profile, after obtaining the media-relative colorimetric
transform of the profile, the PCS-side XYZ tristimulus values for the
ICC-absolute colorimetric intent are calculated, if needed, from the
media-relative colorimetric transform through a simple scaling operation:
Xunder D50 = Xunder D50 mediawhite / X D50 * X mediawhite-relative
Yunder D50 = Yunder D50 mediawhite / YD50 * Ymediawhite-relative
Zunder D50 = Zunder D50 mediawhite / Z D50 * Z mediawhite-relative
Klaus
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