I'm curious... if the RGB values are all accurate, is there a standard color and exposure calibration for paint swatches that is shared across brands?
The white point (color temperature) is easy, using whatever light source they're being illuminated with.
But what determines whether a particular white is (240, 240, 240) or (250, 250, 250) or (255, 255, 255)? The exposure seems far more arbitrary. Is there some kind of maximally bright matte "reference white" material photographed next to each swatch, that then gets calibrated to (255, 255, 255) or similar?
If so, it would be pretty cool if you could buy a reference white chip like that, hold it up to a painted wall in your house, and have an app that could take a photo with both and output the "true" current paint color.
The frontend you see is RGB due to the internet and the display you're using. But on the backend (the manufacturer's system, no idea what the web site employs) the color science is all in spectral data. The xyz color matching functions [1] can be used to determine human response to that spectra, and then to 'CIE L* a* b*' for unambiguously referring to the color. The typical white in the paint industry is CIE illuminant D65.
You're right to wonder about "what is white" which gets into topics of 'chromatic adaptation', 'color constancy', and 'discounting the illuminant'.
If you get a perfectly diffuse white tile, what color is it when illuminant by incandescent versus fluorescent? And there are more than a few CIE F illuminants, and more proprietary ones. And hence each application tends to standardize on, and thus assume, an illuminant. You can use some other illuminant if you want, but then you're in custom territory and it wouldn't surprise me if some companies are doing that, secret sauce.
In special cases like automotive and textiles, it's common to see multiple spectral values due to different colors at different angles, and thus spectrogoniometry.
However color matching is more complex than that. "Color of the light source" varies considerably, not only due to the illuminant itself, but also the materials the illuminant is reflecting off of (e.g. walls). And color temperature only defines black bodies, which most light sources are not: you need information about the full spectrum of the illuminant to determine how it interacts with the material to be color-matched. This is getting a bit into metamerism: https://en.wikipedia.org/wiki/Metamerism_(color) (Of course, paint cannot match an arbitrary spectrum. Matching under specific lighting conditions is the least you can hope for.)
And the above is considering color of a surface only as a scalar value, but it's really a function of illumination angle as well, due to gloss. Direct lighting on a glossy surface reflects more of the color of the gloss, whereas oblique lighting reflects than the paint itself. Diffuse lighting is some combination thereof.
(I am not a color scientist by any means, just interested in the topic. Experts please correct!)
Fascinating. I never knew there was an "standard" mapping between real-world colors and RGB.
Now if only online clothing store photos would map to that, so that the olive green coat I order doesn't turn out to be closer to medium brown or vice-versa... :P
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I'm curious... if the RGB values are all accurate, is there a standard color and exposure calibration for paint swatches that is shared across brands?
The white point (color temperature) is easy, using whatever light source they're being illuminated with.
But what determines whether a particular white is (240, 240, 240) or (250, 250, 250) or (255, 255, 255)? The exposure seems far more arbitrary. Is there some kind of maximally bright matte "reference white" material photographed next to each swatch, that then gets calibrated to (255, 255, 255) or similar?
If so, it would be pretty cool if you could buy a reference white chip like that, hold it up to a painted wall in your house, and have an app that could take a photo with both and output the "true" current paint color.
The frontend you see is RGB due to the internet and the display you're using. But on the backend (the manufacturer's system, no idea what the web site employs) the color science is all in spectral data. The xyz color matching functions [1] can be used to determine human response to that spectra, and then to 'CIE L* a* b*' for unambiguously referring to the color. The typical white in the paint industry is CIE illuminant D65.
You're right to wonder about "what is white" which gets into topics of 'chromatic adaptation', 'color constancy', and 'discounting the illuminant'.
If you get a perfectly diffuse white tile, what color is it when illuminant by incandescent versus fluorescent? And there are more than a few CIE F illuminants, and more proprietary ones. And hence each application tends to standardize on, and thus assume, an illuminant. You can use some other illuminant if you want, but then you're in custom territory and it wouldn't surprise me if some companies are doing that, secret sauce.
In special cases like automotive and textiles, it's common to see multiple spectral values due to different colors at different angles, and thus spectrogoniometry.
[1] https://en.wikipedia.org/wiki/CIE_1931_color_space
You are thinking of a grey card: https://en.wikipedia.org/wiki/Gray_card
However color matching is more complex than that. "Color of the light source" varies considerably, not only due to the illuminant itself, but also the materials the illuminant is reflecting off of (e.g. walls). And color temperature only defines black bodies, which most light sources are not: you need information about the full spectrum of the illuminant to determine how it interacts with the material to be color-matched. This is getting a bit into metamerism: https://en.wikipedia.org/wiki/Metamerism_(color) (Of course, paint cannot match an arbitrary spectrum. Matching under specific lighting conditions is the least you can hope for.)
And the above is considering color of a surface only as a scalar value, but it's really a function of illumination angle as well, due to gloss. Direct lighting on a glossy surface reflects more of the color of the gloss, whereas oblique lighting reflects than the paint itself. Diffuse lighting is some combination thereof.
(I am not a color scientist by any means, just interested in the topic. Experts please correct!)
Ah ha, thanks! So turns out gray cards use "middle gray" which has both a physical definition as well as a specific RGB value:
https://en.wikipedia.org/wiki/Middle_gray
Fascinating. I never knew there was an "standard" mapping between real-world colors and RGB.
Now if only online clothing store photos would map to that, so that the olive green coat I order doesn't turn out to be closer to medium brown or vice-versa... :P