Re: Colormatch vs Adobe 98
Re: Colormatch vs Adobe 98
- Subject: Re: Colormatch vs Adobe 98
- From: "Bruce J. Lindbloom" <email@hidden>
- Date: Fri, 01 Feb 2002 09:32:38 -0600
Don Hutcheson wrote:
>
The point I'm trying to make here is that a typical colorimeter's Lab
>
measurements are based on X-sh, Y-ish, Z-ish filters that simulate the D50
>
spectral weighting functions. The only way to get CIELab(D65) values is
>
either to transform through something like Bradford or to send a signal to
>
the device itself to change it's internal filter mixture factors. I don't of
>
any colorimeters allow that kind of software control, or even support the
>
D50/D65 switching function internally.
With regard to monitor (i.e. emissive) colorimeters, this is simply not
true. The filters in such an instrument are x-ish, y-ish, z-ish (note the
lower case notation for x, y and z) which represent the CIE standard
observer functions. There is nothing inside the instrument that has to do
with any reference illuminant (D50, D65 or anything else). These
colorimeters produce XYZ, not Lab.
For *reflective* colorimeters or spectrophotometers, the XYZ values are
calculated from the integrals of:
a) the reference illuminant
b) the reflectance spectrum of the sample, and
c) each of the three standard observer functions.
For *emissive* colorimeters or spectroradiometers, the XYZ values are
calculated from the integrals of:
a) the spectral power distribution of the emissive source, and
b) each of the three standard observer functions.
Note the absence of a reference illuminant in this second case.
--
Bruce J. Lindbloom
www.brucelindbloom.com