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At some level the fundamental assumptions of a “color” space as a real representation of the human perceptual space is almost comical. The color yellow has been

At some level the fundamental assumptions of a “color” space as a real representation of the human perceptual space is almost comical. The color yellow has been an issue for many decades and diverse combinations of wavelengths evoke identical conscious yellow percepts. The fundamental “not-geometry” of color space is the output of a very complex deep neural net. Thinking about color space as “real” world is almost nonsensical ;-). Trying to map “real” world into brain now has a deservedly bad wrap. Modern philosophy has largely given up on Descartes, sharp subject-object dichotomies, and the brain and mind as a warped mirror of nature. If puzzling at first then check out Humberto Maturana and F. Valera (both experts in color vision electrophysiologist and philosophers), Martin Heidegger, Richard Rorty, and Daniel Dennett have powerful arguments against representationalism of the type implicit in most neuroscience. Valera, Rorty, Dennett are all readable. Heidegger and Matura are more cryptic unless you are a philosopher. https://en.wikipedia.org/wiki/Francisco_Varela https://en.wikipedia.org/wiki/Francisco_Varela Valera’s “The Embodied Mind: Cognitive Science and Human Experience”, co-authored with Evan Thompson and Eleanor Rosch, is a good intro on this and related concepts. But for Hacker News readers by far the best intro to this topic are chapters 4 and 5 of is the CS classic by Terry Winograd and Fernando Flores that is often highlighted on HN. It is a key text in understanding both what goes on in our brains and what is and may go on in machine brains. 1986. Understanding Computers and Cognition: A New Foundation for Design (with Fernando Flores) Ablex Publ Corp

BobbyTables2 2y ago
I’ve always found it deeply disturbing that we ascribe special significance to red/green/blue (that’s only what the eye is best at detecting) as “primary” colors. Why do we teach this to kids? It’s ridiculous that linearly adding “red” and “blue” would make “purple” — all different wavelengths — without a nonlinear effect occurring. CA prism separates these two back out and shows us purple didn’t exist in such an experiment. But we do see “purple” in a rainbow !?!? We see beautiful pictures on LCD screens but we only sense only 3 colors from it? An alien that could see the whole spectrum would think we were completely crazy!
- SAI_Peregrinus 2y ago
  "Purple" is not a spectral color. Violet is, but the purples are a mix of violet & red, or red & blue, or such. Red/green/blue are one set of primaries. Lots of artists working with paint use red/yellow/blue. Inkjet printers use cyan/magenta/yellow. Which colors are "primary" depends on the medium.
  - carlob 2y ago
    Not quite RGB or CYM(K) depends on whether you are adding or subtracting colors i.e. if the light is transmitted or reflected.
    - SAI_Peregrinus 2y ago
      Yes, that's a change of medium. You can also have color-equivalents in non-visible light, such as in frequency-division multiplexing in radio links or fiber optics. Every broadcast TV channel is a different spectral radio color (well, a small range of them).
DiscourseFan 2y ago
>Heidegger and Matura are more cryptic unless you are a philosopher. I think The Origin of the Work of Art by Heidegger is fairly readable. I'd also add one of Heidegger's classmate's, Walter Benjamin, whose early writing was directly about the experience of color. There's a book about it called Walter Benjamin, The Colour of Experience by Howard Caygill. Though its a bit difficult for the layman because it interprets Benjamin through his neokantian education (at the Marburg school, with Heidegger) and assumes a certain familiarity with Kant.
mpweiher 2y ago
The concept of color spaces for human color perception is deeply and solidly anchored in the structure of the human visual system. Different kinds of color spaces in different parts of that system. The additive "RGB" colorspace has to do with the fact that we have 3 different types of color cones in our eyes, which have different spectral sensitivities. Any color perception that we can register is a combination of these three signals. Hence a three-dimensional space. https://en.wikipedia.org/wiki/CIE_1931_color_space https://en.wikipedia.org/wiki/CIE_1931_color_space The RGB primaries that we choose for monitors do not match these color sensitivities, but also map to a space that is made to overlap with our perceptual space. > The color yellow has been an issue for many decades and diverse combinations of wavelengths evoke identical conscious yellow percepts. No. Metamerism is a general property of human color perception. For each color we can perceive there are a vast number of spectral distributions that can produce that particular color. https://en.wikipedia.org/wiki/Metamerism_(color) https://en.wikipedia.org/wiki/Metamerism_(color) One of the many reasons a purely physical approach is both too difficult and insufficient for color management. In addition to these physical color spaces, there are perceptual color spaces, my favorite one being CIE Lab, an opponent color space. With CIE Lab, the L component is overall luminosity, a is a red-green difference and b is blue-yellow difference. This corresponds to color processing that occurs after the initial signal is received and closely matches how humans actually subjectively perceive color, philosophical (im)ponderables aside. https://en.wikipedia.org/wiki/CIELAB_color_space https://en.wikipedia.org/wiki/CIELAB_color_space
- canjobear 2y ago
  > Any color perception that we can register is a combination of these three signals. Hence a three-dimensional space. Only approximately. In the linked article you can see that the color gamut is a horseshoe shape that cannot be fully spanned by a triangle. So there are color percepts such as responses to pure wavelengths that can’t be reproduced as combinations of real primaries. You could invent imaginary primary colors to make it work, hence the XYZ color space. In any case, the whole point of TFA is that a space is not an adequate characterization of color percepts, because there is no Riemannian geometry that matches the psychophysical data.
JadeNB 2y ago
> The color yellow has been an issue for many decades and diverse combinations of wavelengths evoke identical conscious yellow percepts. How can you possibly determine whether different stimuli evoke identical percepts? (I don't know a technical definition of ‘percept,’ but am assuming that it carries some additional data beyond something that can be directly measured from brain activity. If not, then I withdraw my question.)
- gmueckl 2y ago
  Historically, this has been determined by presenting stimuli simultaneously and asking the subject about their similarity; alternatively by presenting a reference stimulus next to a tunable stimulus (e.g. red, green and blue monochromatic light sources) and asking the subject to match the two stimuli as closely as possible.
  - _nalply 2y ago
    And for animals like dogs and some birds, set up a reward system, train the animal, then run tests and deduct what can be seen by the behavior of the trained animal. Dogs see only two colors, this means compared to humans they are color-blind (or something like red-green blind).

BobbyTables2 2y ago

I’ve always found it deeply disturbing that we ascribe special significance to red/green/blue (that’s only what the eye is best at detecting) as “primary” colors. Why do we teach this to kids? It’s ridiculous that linearly adding “red” and “blue” would make “purple” — all different wavelengths — without a nonlinear effect occurring. CA prism separates these two back out and shows us purple didn’t exist in such an experiment. But we do see “purple” in a rainbow !?!? We see beautiful pictures on LCD screens but we only sense only 3 colors from it? An alien that could see the whole spectrum would think we were completely crazy!

SAI_Peregrinus 2y ago
"Purple" is not a spectral color. Violet is, but the purples are a mix of violet & red, or red & blue, or such. Red/green/blue are one set of primaries. Lots of artists working with paint use red/yellow/blue. Inkjet printers use cyan/magenta/yellow. Which colors are "primary" depends on the medium.
- carlob 2y ago
  Not quite RGB or CYM(K) depends on whether you are adding or subtracting colors i.e. if the light is transmitted or reflected.
  - SAI_Peregrinus 2y ago
    Yes, that's a change of medium. You can also have color-equivalents in non-visible light, such as in frequency-division multiplexing in radio links or fiber optics. Every broadcast TV channel is a different spectral radio color (well, a small range of them).

DiscourseFan 2y ago

>Heidegger and Matura are more cryptic unless you are a philosopher. I think The Origin of the Work of Art by Heidegger is fairly readable. I'd also add one of Heidegger's classmate's, Walter Benjamin, whose early writing was directly about the experience of color. There's a book about it called Walter Benjamin, The Colour of Experience by Howard Caygill. Though its a bit difficult for the layman because it interprets Benjamin through his neokantian education (at the Marburg school, with Heidegger) and assumes a certain familiarity with Kant.

mpweiher 2y ago

The concept of color spaces for human color perception is deeply and solidly anchored in the structure of the human visual system. Different kinds of color spaces in different parts of that system. The additive "RGB" colorspace has to do with the fact that we have 3 different types of color cones in our eyes, which have different spectral sensitivities. Any color perception that we can register is a combination of these three signals. Hence a three-dimensional space. https://en.wikipedia.org/wiki/CIE_1931_color_space https://en.wikipedia.org/wiki/CIE_1931_color_space The RGB primaries that we choose for monitors do not match these color sensitivities, but also map to a space that is made to overlap with our perceptual space. > The color yellow has been an issue for many decades and diverse combinations of wavelengths evoke identical conscious yellow percepts. No. Metamerism is a general property of human color perception. For each color we can perceive there are a vast number of spectral distributions that can produce that particular color. https://en.wikipedia.org/wiki/Metamerism_(color) https://en.wikipedia.org/wiki/Metamerism_(color) One of the many reasons a purely physical approach is both too difficult and insufficient for color management. In addition to these physical color spaces, there are perceptual color spaces, my favorite one being CIE Lab, an opponent color space. With CIE Lab, the L component is overall luminosity, a is a red-green difference and b is blue-yellow difference. This corresponds to color processing that occurs after the initial signal is received and closely matches how humans actually subjectively perceive color, philosophical (im)ponderables aside. https://en.wikipedia.org/wiki/CIELAB_color_space https://en.wikipedia.org/wiki/CIELAB_color_space

canjobear 2y ago
> Any color perception that we can register is a combination of these three signals. Hence a three-dimensional space. Only approximately. In the linked article you can see that the color gamut is a horseshoe shape that cannot be fully spanned by a triangle. So there are color percepts such as responses to pure wavelengths that can’t be reproduced as combinations of real primaries. You could invent imaginary primary colors to make it work, hence the XYZ color space. In any case, the whole point of TFA is that a space is not an adequate characterization of color percepts, because there is no Riemannian geometry that matches the psychophysical data.

JadeNB 2y ago

> The color yellow has been an issue for many decades and diverse combinations of wavelengths evoke identical conscious yellow percepts. How can you possibly determine whether different stimuli evoke identical percepts? (I don't know a technical definition of ‘percept,’ but am assuming that it carries some additional data beyond something that can be directly measured from brain activity. If not, then I withdraw my question.)

gmueckl 2y ago
Historically, this has been determined by presenting stimuli simultaneously and asking the subject about their similarity; alternatively by presenting a reference stimulus next to a tunable stimulus (e.g. red, green and blue monochromatic light sources) and asking the subject to match the two stimuli as closely as possible.
- _nalply 2y ago
  And for animals like dogs and some birds, set up a reward system, train the animal, then run tests and deduct what can be seen by the behavior of the trained animal. Dogs see only two colors, this means compared to humans they are color-blind (or something like red-green blind).