Re: D vs K
Re: D vs K
- Subject: Re: D vs K
- From: "Bruce J. Lindbloom" <email@hidden>
- Date: Fri, 24 Jan 2003 10:43:26 -0600
Sven Westerlund wrote:
>
What4s the different between D65 and 6500K(or D50 and 5000K)
D65 is a spectral power distribution, or SPD (i.e. a certain amount of
energy wavelength by wavelength across the visible spectrum). This spectrum
may be calculated for any correlated color temperature using formulas and
tables published by the CIE. You plug 6500 into the formulas and out pops
the D65 SPD. This is a jagged looking spectrum.
A blackbody radiator whose temperature is 6500 degrees Kelvin emits an SPD
which may be calculated using Planck's formula. Plug in 6500 and out pops
the blackbody SPD. This is a smooth spectrum, but generally similar to the
D65 SPD.
(You may graphically view these and other spectra here:
<
http://www.brucelindbloom.com/CIESpectralCalculator.html>.)
Any spectrum, when "viewed" with the CIE standard observer functions,
produces XYZ or xyY.
There are many different spectra that can produce the same xyY (a
many-to-one mapping). So given a spectrum, you can determine its xyY, but
given an xyY, you cannot determine its spectrum.
Most xyY colors can be expressed as a "correlated color temperature" which
is determined by finding the temperature of a blackbody radiator whose color
is "closest" to it. There are many different xyY colors that have the same
correlated color temperature (another many-to-one mapping). So given an xyY,
you can determine its correlated color temperature, but given a correlated
color temperature, you cannot determine its xyY (nor its spectrum as just
mentioned).
So a spectrum is very precise and unique. Its xyY is less precise and
unique. Its correlated color temperature is even less precise and unique.
Getting back (finally) to the original question, D65 is a unique SPD (there
exists only one). A color whose correlated color temperature is 6500K is not
unique (there are infinitely many different xyY and SPDs that share it).
How's that for a long answer to a short question?
--
Bruce J. Lindbloom
email@hidden
http://www.brucelindbloom.com
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