Re: D65 isn't 6500k?
Re: D65 isn't 6500k?
- Subject: Re: D65 isn't 6500k?
- From: "Bruce J. Lindbloom" <email@hidden>
- Date: Tue, 03 Dec 2002 12:17:45 -0600
Jeff MacWright wrote:
>
When I choose D65 or 6500k with OptiCal there is a visible shift and when I
>
use the Spyder as a colorimeter reading the difference is confirmed. I
>
always assumed that the D65 is 6500k, isn't it?
I don't know anything about OptiCal, so I can happily plead ignorance there.
But regarding the D65/6500K issue, there are specific definitions which are
often misunderstood or misused by people. Here are five ways to interpret
these terms:
a) D65 is a spectral power distribution (a certain amount of energy at each
wavelength across the visible spectrum).
b) D65 tristimulus value. The D65 spectrum, when "viewed" by the CIE
standard observer, produces an XYZ triplet (or xyY if you prefer).
c) 6500K blackbody radiator is a spectral power distribution.
d) 6500K blackbody tristimulus value. The 6500K blackbody spectrum, when
viewed by the CIE standard observer, produces an XYZ triplet -- similar to,
but slightly different from the one found in "b" above.
e) Correlated Color Temperature takes a color's chromaticity coordinate (x,
y) and finds the particular blackbody temperature whose chromaticity
coordinate ("d" above) is "closest" to it. Note that there are many
different colors that have the same correlated color temperature.
As I stated above, I don't know how OptiCal works, but it cannot possibly
make your monitor's spectral power distribution match either D65 or a 6500K
blackbody radiator ("a" and "c"). It would not be useful if it matched the
correlated color temperature ("e") since there are many colors that would
qualify, and most of these candidates are far from neutral.
Therefore, I would guess that OptiCal's D65 tries to match "b" above, and
6500 tries to match "d" above. If one of these OptiCal options behaves
erratically (as some on this list have reported), I would say it is a
software bug, since "b" and "d" would produce results that are nearly
identical.
BTW, if you want to see what a D65 spectrum and a 6500K blackbody spectrum
look like you can examine them here:
<
http://www.brucelindbloom.com/CIESpectralCalculator.html>. If you want to
find the correlated color temperature of a color, you can do it here:
<
http://www.brucelindbloom.com/ColorCalculator.html>.
--
Bruce J. Lindbloom
email@hidden
http://www.brucelindbloom.com
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