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The Context

I am exploring the idea of making a DIY spectrometer(and colorimeter) for testing various material samples for interior visualization. It's sort of a hobby project for my curiosity and pleasure that might end up useful for my actual work with CG.

The Question

I am struggling to find a trustworthy information source for light wavelengths sRGB color space primaries are supposed to be. They are supposed to be the same as in REC.709 as far as I understand. Are the actual wavelengths of sRGB RGB primaries defined and if so what are they in nanometers?

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  • $\begingroup$ RGB are computed as weighted integrals over a whole range of wavelengths. I don't have the weight curves however. Never mind, I found this: en.wikipedia.org/wiki/… $\endgroup$
    – lightxbulb
    Jan 7, 2021 at 19:19

2 Answers 2

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Trichromatic color system is based on using 3 carefully selected reference spectral power distributions(SPD) as you imagine. CIE uses its own reference SPDs, but there are others who prefer using other SPDs as reference. So the answer to the question

Are the actual wavelengths of sRGB RGB primaries defined and if so what are they in nanometers?

differs, or might differ, with respect to institutions. As for trustworthy resources:

Scott Burns had kindly provided some reference SPDs in his website.

For illuminants and observers etc. you can check the website of Munsell Color Science Lab.

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  • $\begingroup$ Thank you. This is exactly what I was looking for. It will be interesting to compare the SPDs of primaries of real monitors with this if I ever manage to make the spectrometer. $\endgroup$ Jan 8, 2021 at 8:45
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The primaries of sRGB are not pure wavelengths, they are color mixtures. Their true definition is in terms of CIE chromaticity coordinates. That said, for sRGB, the red primary is close-ish to 610nm, green is very roughly 555nm, and blue is close-ish to 465nm.

The Rec. 2020 RGB space, by the way, is actually defined using pure wavelengths for the primaries: R=630nm, G=532nm, and B=467nm.

Various RGB gamuts plotted in CIE chromaticity coordinates

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    $\begingroup$ Right, but it might be better that you do not say "color mixtures"when you mean wavelength distributions. Because it makes the subject matter confusing as now colpr has many meaning. $\endgroup$
    – joojaa
    Jan 8, 2021 at 6:49
  • $\begingroup$ Thank you, this is very helpful. together with the the answer of Kaan E., this pretty much answer my question. $\endgroup$ Jan 8, 2021 at 8:42
  • $\begingroup$ @joojaa I could say that they are a wavelength distribution or a spectral mixture, but I think this is also confusing as these primaries are not defined to be a specific SPD. They are defined in terms of chromaticities which can be represented metamerically by an infinity of different SPDs. $\endgroup$ Jan 8, 2021 at 18:35
  • $\begingroup$ @Nathan yes i understand that. Our everyday language is not terribly good vhen we reach this level of abstraction. But still... $\endgroup$
    – joojaa
    Jan 9, 2021 at 9:15

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