# Talk:Dominant wavelength

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## CIE calibration arbitraryness

On the CIE color coordinate space, a straight line drawn between a given color and the coordinates for standard white (1/3,1/3) can be extrapolated out ...

I have a feeling that the given definition is somewhat arbitrary. The sensitivity spectra of the three types of rods[sic] have a well-defined shape, but there is no absolute way to determine the ratios between the sensitivities at any particular wavelength. CIE 1936 uses the arbitrary definition that the surfaces on the three curves (with wavelength on the horizontal axis) are equal, which means that a flat spectrum results in X,Y=1/3,1/3. I, being a spectroscopist, am more used to spectra with frequency on the horizontal axis, which would result in a completely different diagram if the normalization were done according to that spectrum. One could also have normalized the curves to give equal responses for 6000 K sunlight, or in a way which makes the steps in wavelength along the border more constant—the 1936 CIE has too much emphasis on green colors. Each of the infinitely many ways to calibrate the color space would result in a different definition "dominant wavelength" and CIE is only one of them. Although, now that I'm thinking of it, the tristimulus space :image:gamut_full.png would have the same cross-section, so maybe it is mainly the definition of the "white point" that should bother me.

Furthermore, the point 1/3,1/3 does not correspond to a white from a blackbody radiator,[sic] it is slightly of the "color temperature" curve. This is a less-important point since it makes sense to talk about a dominant wavelength compared to a flat spectrum that has no dominant wavelength. -- Hankwang 19:49, 20 Mar 2004 (UTC)

The article looks good to me, though it could very much benefit from some diagrams, especially for the paragraph discussing lines intersecting parts of the CIE space graph. Having a couple of frequency-component graphs might be good too, in order to illustrate the concept of "this color has many component frequencies; this other color has only one component frequency; because of the way dominant wavelength works, they look like the same color to humans." Bringing up another point—does this principle work for organisms that have better or worse color perception than humans? If so, how is it different for other organisms? And how does it relate to mechanical color perception (such as a digital camera or photo scanner)? Devices that, like humans, only sense color through stimulus of a few specifically-tuned receptors (like RGB)? -- Wapcaplet 01:28, 25 Mar 2004 (UTC)

I agree about the examples. This article, like many on Wikipedia is pointlessly over technical, some simple picture examples could be worth a thousand words.
An organism or machine with more photoreptors would be able to distinguish finer nuances in the spectral composition of a light beam. Where we infer yellow from a stimulation of our red and green receptors, something that actually had additional yellow receptors would percieve a difference between pure yellow versus red+green. That's my understanding anyway. If something only had red and blue receptors (no green) it shouldn't be able to distiguish between green and purple. I guess that explains how color blindness works. Lomacar (talk) 18:37, 24 January 2008 (UTC)