Re: RelCol Mapping of Middle Gray
Re: RelCol Mapping of Middle Gray
- Subject: Re: RelCol Mapping of Middle Gray
- From: Ken Fleisher <email@hidden>
- Date: Mon, 07 Mar 2005 20:47:45 -0500
Actually, it sounds like you are getting the correct values. Remember
that ICC L*a*b* is NOT the same as CIE L*a*b*.
In ICC L*a*b*, the white point of the media is used instead of the
white point of D50 (it's assuming that you are chromatically adapted to
the white point of the media). Therefore values of L*=100, a*=0, b*=0
represent, by definition, the white point of the media, not the light
source. If you want to make a direct comparison using your
spectrophotometer and ICC L*a*b* values, then you must also factor in
the white point of your media when calculating L*a*b* (which your
spectrophotometer is NOT doin--if that is where you are getting the
values from). The fact that you are getting the same a*b* values as
your white point is therefore correct.
To calculate into ICC L*a*b*, you can take your XYZ values from your
spectrophotometer (D50 and two degree observer) and convert to L*a*b*
using the media white point (instead of D50). This should then result
in a*b* values of 0 for neutral colors and match the values that the
profile is trying to make.
Ken
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