I sort of wonder is there a "true" way to represent color? Would a intensity over frequency curve do it?
I probably lack the terminology to express myself properly, but color ends up being a very human thing, with a huge focus on primary colors(the colors that match the frequency response of the human eye) This is fine, we are human after all, but then I always feel color theory dives off the deep end, with color wheels and complimentary colors and triplets, etc. why? there is nothing physically cyclic going on. It never makes any sense to me that patterns based on it being cyclic would be any better than just picking colors. Any way, silly rant aside, if we wanted to define an objective physical color format, how would it be done?
If you plot the three primary colors with all possible combinations of only two of them, you can connect them all neatly using a circle, and distance on that circle does tell us something about how visually distinct colors are. It isn't much more profound than that.
One of the colors on the circle, magenta, has no corresponding pure wavelength, because in order to see magenta, your red and blue cones must be activated, but not the green cones -- you need two frequency peaks to do this. If we had four different types of cones, like many birds, there would be many more non-spectral fully saturated colors and you'd need something like a hypercube to represent them.
You could go a long way by specifying the reflectiveness over the visible light spectrum and then do the same for light sources. That way, you could do GDR style truly monochrome sodium vapor lamps, which makes telling colors apart impossible.
To do neon colors, you would need some sort of frequency redirect in your texture data as in "this pixel absorbs 80% infrared, but reemits it as visible red". Then you could have black light light sources and cool poster textures as well.
I think doing textures in this format would take too much space, but doing a 256 color palette that way might be fine.
That should work as a brute-force method. You could simulate lighting conditions by measuring the reflected spectrum of different materials and multiplying with the spectrum of a light source.
Check out the CIE XYZ color space and its color matching functions. It's the standard for defining/converting color spaces and calibrating displays for accurate color matching. It only models human perception, and contains colors that are physically impossible to reproduce.
Depending on what you want to do there's CIE XYZ (maps spectrum of color to a 3 component vector by integrating the spectrum multiplied by three functions), CIE Lab* (describes the color of objects under a specified illuminant), CIE Luv* (to characterize emissive source, nonlinear so the the distance between colors corresponds to perceived differences).
These color spaces are built to objectively describe colors, as seen by a human with typical color vision.
> I sort of wonder is there a "true" way to represent color? Would an intensity over frequency curve do it?
There’s no single “true” way because color isn’t a fixed property of light itself, it’s the result of how a visual system interprets wavelengths.
Having said that, if you’re looking for an objective way that doesn’t depend on observer, you could use spectral power distribution.
That would be the mix of wavelengths present, plotted as intensity vs. wavelength.
That’s because a single wavelength (say 580nm) produces one specific color sensation, but many different combinations of wavelengths can produce that identical sensation (called metamers), so representing color by wavelength alone isn’t even uniquely “true” perceptually.
“I’ve thought about this for five minutes, and it seems so simple. It must be the tens of thousands of vision scientists and psychophysicists who have worked on this for the last century who have all missed how simple it is.”
CRI of lights is definitely a large factor in my purchasing these days. The muting, compressive response of some lights almost pains me at this point.
As this post's author noted white LEDs can be pretty solid. Bulbs that have a mix of white LEDs at various temperatures to be "bi-color" tend to be pretty solid as well. Its once you go towards RGB light bulbs that you tend to get a fairly iffy CRI.
https://en.wikipedia.org/wiki/Black-body_radiation As objects get hotter and start glowing, they start to emit radiation in visible frequencies. Very hot objects keep glowing in the redder parts as they also start to glow in higher bands. Our eyes collect all the various frequencies at different intensities and experience them as one color. The second diagram on the page, with the chromaticity of different temperatures of ideal black-body radiators, shows the color that we perceive as the temperature of the glowing object goes up. The sun is around 5800k, so a little bit in in the yellow-green direction from perfectly balanced color response.
Sure, the sun is white, more or less (cf comments re human perception and what "white" really means).
But when did humans first perceive the sun as white? We can only reliably say "sometime on or after 12 April 1961", the day Gagarin went into space. Prior to that, as far as we know, all humans saw the sun as some other colour, most often yellow or red, depending on the time of day.
Since Newton's prism, we had pretty good reason for believing it was likely white, reasons that got stronger in the 19th C with improved theories of optics, the discovery of atomic spectra, etc. I'm curious to know when we confirmed for sure its whiteness, and whether this was before October 1957 (Sputnik) or after Gagarin or somewhere in between.
The direct light from the Sun is yellowish, because the blue light of the sky is subtracted from it.
If the sky is covered with clouds, then the light is white, because the blue sky light is mixed again with the direct Sun light.
If the sky is clear and there is an unobstructed view of it, the light reflected by a white object will be the sum of the light coming from the sky to the object and directly from the Sun to the object, so it will be white. For example this is true for white clouds and white snow.
This, i.e. that the Sun outside the atmosphere is perfectly white, has been understood for a long time, since the 19th century.
There are no objective "basic colors". What "white" means is "excites our different types of photoreceptors roughly equally". And the photoreceptors have the sensitivity curves that they do because of our sun’s surface temperature and a convenient "window" in the opacity of our atmosphere. Organisms evolved under a different star, within a different atmosphere would have a different idea of what a "neutral" color is.
(Because of additional processing done by our visual system, what looks "white" to us is very dependent on the color of the ambient light. But the ~5800 K blackbody spectrum could be called the "most neutral" white to our eyes because that’s what evolution has optimized them for.)
It's a convention. And at one time it was useful as the thing that could be replicated anywhere.
Also, things that are white can be judged by the amount of light they reflect or scatter as a percentage, independent of the source of illumination. For instance, among familiar objects, a common white ceramic bathroom tile comes pretty close to pure white.
I sort of wonder is there a "true" way to represent color? Would a intensity over frequency curve do it?
I probably lack the terminology to express myself properly, but color ends up being a very human thing, with a huge focus on primary colors(the colors that match the frequency response of the human eye) This is fine, we are human after all, but then I always feel color theory dives off the deep end, with color wheels and complimentary colors and triplets, etc. why? there is nothing physically cyclic going on. It never makes any sense to me that patterns based on it being cyclic would be any better than just picking colors. Any way, silly rant aside, if we wanted to define an objective physical color format, how would it be done?
> there is nothing physically cyclic going on
If you plot the three primary colors with all possible combinations of only two of them, you can connect them all neatly using a circle, and distance on that circle does tell us something about how visually distinct colors are. It isn't much more profound than that.
One of the colors on the circle, magenta, has no corresponding pure wavelength, because in order to see magenta, your red and blue cones must be activated, but not the green cones -- you need two frequency peaks to do this. If we had four different types of cones, like many birds, there would be many more non-spectral fully saturated colors and you'd need something like a hypercube to represent them.
You could go a long way by specifying the reflectiveness over the visible light spectrum and then do the same for light sources. That way, you could do GDR style truly monochrome sodium vapor lamps, which makes telling colors apart impossible.
To do neon colors, you would need some sort of frequency redirect in your texture data as in "this pixel absorbs 80% infrared, but reemits it as visible red". Then you could have black light light sources and cool poster textures as well.
I think doing textures in this format would take too much space, but doing a 256 color palette that way might be fine.
“ultraviolet”, not infrared. IR to visible light would be upconversion.
https://en.wikipedia.org/wiki/Photon_upconversion
> Would a intensity over frequency curve do it?
That should work as a brute-force method. You could simulate lighting conditions by measuring the reflected spectrum of different materials and multiplying with the spectrum of a light source.
Check out the CIE XYZ color space and its color matching functions. It's the standard for defining/converting color spaces and calibrating displays for accurate color matching. It only models human perception, and contains colors that are physically impossible to reproduce.
https://en.wikipedia.org/wiki/CIE_1931_color_space
The term you're looking for is "color space".
Depending on what you want to do there's CIE XYZ (maps spectrum of color to a 3 component vector by integrating the spectrum multiplied by three functions), CIE Lab* (describes the color of objects under a specified illuminant), CIE Luv* (to characterize emissive source, nonlinear so the the distance between colors corresponds to perceived differences).
These color spaces are built to objectively describe colors, as seen by a human with typical color vision.
> I sort of wonder is there a "true" way to represent color? Would an intensity over frequency curve do it?
There’s no single “true” way because color isn’t a fixed property of light itself, it’s the result of how a visual system interprets wavelengths.
Having said that, if you’re looking for an objective way that doesn’t depend on observer, you could use spectral power distribution.
That would be the mix of wavelengths present, plotted as intensity vs. wavelength.
That’s because a single wavelength (say 580nm) produces one specific color sensation, but many different combinations of wavelengths can produce that identical sensation (called metamers), so representing color by wavelength alone isn’t even uniquely “true” perceptually.
Colors only exist in the human brain, they're qualia, interpreted from the mixture of wavelengths our eyes detect.
“I’ve thought about this for five minutes, and it seems so simple. It must be the tens of thousands of vision scientists and psychophysicists who have worked on this for the last century who have all missed how simple it is.”
Thanks for this comparison. Very interesting and surprising!
CRI of lights is definitely a large factor in my purchasing these days. The muting, compressive response of some lights almost pains me at this point.
As this post's author noted white LEDs can be pretty solid. Bulbs that have a mix of white LEDs at various temperatures to be "bi-color" tend to be pretty solid as well. Its once you go towards RGB light bulbs that you tend to get a fairly iffy CRI.
I've referenced https://optimizeyourbiology.com/light-bulb-database and https://optimizeyourbiology.com/smart-light-database before when looking at bulbs but if anyone has a better resource, absolutely please drop a reply.
I'd be curious to understand exactly how CRI equates to the charts in this post!
You basically measure the light source with a spectrophotometer, then perform the procedure in https://en.wikipedia.org/wiki/Color_rendering_index
Alternatively you buy a ColorChecker chart and measure the reflected light with a colorimeter.
Basically, the finer the color separation, wider the gamut, and whiter the light, the higher the CRI.
Sun is white light. Wonder what that means. Brightest object in out awareness is modeled as clean white. Or is this the actual basic color.
https://en.wikipedia.org/wiki/Black-body_radiation As objects get hotter and start glowing, they start to emit radiation in visible frequencies. Very hot objects keep glowing in the redder parts as they also start to glow in higher bands. Our eyes collect all the various frequencies at different intensities and experience them as one color. The second diagram on the page, with the chromaticity of different temperatures of ideal black-body radiators, shows the color that we perceive as the temperature of the glowing object goes up. The sun is around 5800k, so a little bit in in the yellow-green direction from perfectly balanced color response.
Sure, the sun is white, more or less (cf comments re human perception and what "white" really means).
But when did humans first perceive the sun as white? We can only reliably say "sometime on or after 12 April 1961", the day Gagarin went into space. Prior to that, as far as we know, all humans saw the sun as some other colour, most often yellow or red, depending on the time of day.
Since Newton's prism, we had pretty good reason for believing it was likely white, reasons that got stronger in the 19th C with improved theories of optics, the discovery of atomic spectra, etc. I'm curious to know when we confirmed for sure its whiteness, and whether this was before October 1957 (Sputnik) or after Gagarin or somewhere in between.
The direct light from the Sun is yellowish, because the blue light of the sky is subtracted from it.
If the sky is covered with clouds, then the light is white, because the blue sky light is mixed again with the direct Sun light.
If the sky is clear and there is an unobstructed view of it, the light reflected by a white object will be the sum of the light coming from the sky to the object and directly from the Sun to the object, so it will be white. For example this is true for white clouds and white snow.
This, i.e. that the Sun outside the atmosphere is perfectly white, has been understood for a long time, since the 19th century.
There are no objective "basic colors". What "white" means is "excites our different types of photoreceptors roughly equally". And the photoreceptors have the sensitivity curves that they do because of our sun’s surface temperature and a convenient "window" in the opacity of our atmosphere. Organisms evolved under a different star, within a different atmosphere would have a different idea of what a "neutral" color is.
(Because of additional processing done by our visual system, what looks "white" to us is very dependent on the color of the ambient light. But the ~5800 K blackbody spectrum could be called the "most neutral" white to our eyes because that’s what evolution has optimized them for.)
It's a convention. And at one time it was useful as the thing that could be replicated anywhere.
Also, things that are white can be judged by the amount of light they reflect or scatter as a percentage, independent of the source of illumination. For instance, among familiar objects, a common white ceramic bathroom tile comes pretty close to pure white.
White light is that which is perceived as white, and that corresponds to light sources who color approximates a black body like the Sun.