Re: CRT Colorimetry woes
Re: CRT Colorimetry woes
- Subject: Re: CRT Colorimetry woes
- From: Roger Breton <email@hidden>
- Date: Fri, 30 May 2003 15:24:26 -0400
>
One apparent misconception is relating between relative Y values with
>
absolute luminance level - there is no such relation. Easiest way to
>
find out the truth is to take a spectral measure of the patch and of the
>
white point of the monitor with I1 and convert it to XYZ; but you have
>
to decide first relative to which illuminant you're going to calculate
>
it - the actual monitor's or one of the standards - D50 etc. If you need
>
the values relative to your monitor's white point, so since you've
>
measured the whitepoint itself then the DTP92 readings under colorshop
>
are closer to the real thing since the Y is suppose to be 100...
Boris,
I did measure with my EyeOne in spectral mode. If I want to convert the
measured spectral radiance (W/sr/m2) to CIE Tristimulus values (XYZ) I have
to apply the weighted ordinate method as per CIE Publication 15.2
"Colorimetry". In the case of a source (or more aptly an 'extended' source,
like in the case of a CRT), AFAIK and as far as I understand what you wrote,
there is no illuminant involved, unlike when obtaining the tristimulus
values for a surface (printed) color where some illuminant must be factored
in to account for the varying appearance of color.
This being said, I did measure my monitor with my EyeOne in spectral mode
and I got X=79.5 Y=83.6 Z=68.7. The luminance, Y=83.6, is more in line with
what I believe the real luminance of my monitor is.
To put this new set of measurement in perspective, let me add it to the
previously reported table:
------------ DTP92 ------------ ---------- i1 ---------
ColorShop OptiCal MeasureTool MeasureTool MeasureTool
2.6.2 3.7.5 4.1.5 4.1.5 Spectral
Classic OSX OSX OSX Mode
== ========= ======= =========== ========= =========
X 94.00 77.79 75.7 70.0 79.5
Y 97.92 80.91 81.5 74.1 83.6
Z 83.92 68.78 57.0 61.6 68.7
You can see that OptiCal with my newly calibrated DTP92 and MeasureTool with
my EyeOne, in spectral mode, yield the best estimate of what I consider my
true monitor Tristimulus values.
Regards,
Roger Breton
Laval, Canada
email@hidden
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