Wikipedia:Reference desk/Archives/Science/2018 August 2

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August 2

Explain why these 2 statements are not contrary to each other

Receptivity of human vision receptors in the visible spectrum

1. According to opponent process, there's no such color as reddish green.
2. According to RGB color theories, yellow is reddish green. RGB color theories suggest there's no reddish cyan or greenish magenta, but yellow is reddish green. Georgia guy (talk) 23:52, 2 August 2018 (UTC)

"Even though yellow is a mixture of red and green in the RGB color theory, the eye does not perceive it as such." ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:00, 3 August 2018 (UTC)

I assume that you've read Impossible color. More than fifty years ago, I tried holding a good red filter to one eye and a good green filter to the other, and I saw in yellow (not reddish green). My interpretation was that the brain (not the eye) interprets roughly equal stimulations of L and M cones as being the colour yellow. I haven't tried rapid alternation between the two colours. Perhaps I might see that differently as being "reddish green". Colour perception is partly learnt and partly hard-wired. Dbfirs 08:26, 3 August 2018 (UTC)

In a graphics program (e.g. MSpaint) if you select a custom color with red and green at max (255) and blue at 0, you get yellow -- this is not a "perception" of either the eye or brain. 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 14:17, 3 August 2018 (UTC)

No, it's your brain telling you that its yellow. Absolutely no light of the 580nm range is leaving the monitor. The monitor has zero yellow pixels in it. Your perception of yellow from a monitor is a purely psychological phenomenon. Actually, all of your perception of color is a purely psychological phenomenon. See qualia and color perception. If you really want to get down to it, you have never seen yellow, because your eye is only capable of detecting basically 3 colors; red, blue, and green, and your perception of yellow is dependent only on how much of each of those receptors is stimulated by a particular bit of light. You can stimulate all three with a single wavelength of yellow light, OR you can stimulate all three with varying intensities of red, green, and blue light and you can't tell the difference. Because you don't see yellow. --Jayron32 14:58, 3 August 2018 (UTC)

It depends on your definition of "yellow" -- a can of yellow paint has paint that is yellow in color.— Preceding unsigned comment added by 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk • contribs)

Actually, it depends on your definition of "color". If you're defining color as the psychological sensation that looking at the yellow paint produces, then yes. If you're defining color as a specific wavelength of electromagnetic radiation, then maybe not so much. The relationship between color you perceive when looking at something and the wavelength of the light in question is tenuous at best. --Jayron32 15:21, 3 August 2018 (UTC)

While not disagreeing with the general thrust of your comments, the relationship is not really "tenuous" in any sense; there is a direct, causal biophysical relationship between those two things. It's simply that colour as a percept and as a form of qualia is not a product solely of the stimulus of any one photoreceptive cell. Indeed, despite our intuitive feelings to the contrary, as a scientific and ontological matter, both physicists and cognitive scientists working in this area would hold your basic assertion to be correct: "Colour" does not exist as a physical property of light, but rather as a purely mental phenomena. But the relationship between the physical properties of the photon that strikes an opsin chain and the biophysical and neurological series of reactions that result in the ultimate perception of colour is actual and empirically quantifiable in a variety of ways. There is no "colour" encoded in the interaction between the light and the photoreceptor--that, rather, is the product of higher level work in the brain where the information from a vast number of such cells is integrated together--but the perception of colour is absolutely triggered and shaped by the stimulus nevertheless, and the relationship is thus not a tenuous one, but rather one which is highly direct and as consistent as any other property of the interaction of light with matter. Snow ^{let's rap} 01:46, 6 August 2018 (UTC)

Yes, thanks for the additional detail. Good stuff! --Jayron32 15:15, 6 August 2018 (UTC)

• Responding to the OP, it's basically a distinction between the eye and brain. On one hand, the eye contains three types of color-sensitive cones, so the signals leaving the eye can be represented using three independent color dimensions, typically thought of as R, G, and B. However, in the color-processing parts of the visual cortex, the signals are recoded into hue, saturation, and intensity. The hue component can be represented as a circle, with four canonical hues spaced equally around it: red, yellow, green, and blue. Looie496 (talk) 02:38, 4 August 2018 (UTC)

  You can represent hue as anything, I've seen the circle heuristic before, though roundy-triangles seems to be the vogue for more detailed representations of color space. Historically, the CIE 1931 color space was the first attempt to quantify human color perception in such terms; there have been some updates to it over time, but it remains something of a standard. --Jayron32 15:21, 4 August 2018 (UTC)

• I will assume the OP is familiar with the stuff described here (IMO an excellent explanation of RGB and vision) (the IPv6 editor above clearly is not, but answers have been provided to that mini thread-hijack).

The answer is that the first premise is incorrect. reddish green is allowed by the opponent process theory, it just means (going by the diagram in the article) that in neurological processes it is treated as "some luminosity, no R-G, high R+G-B". This is different from other colors, e.g. white (high luminosity, no R-G, low R+G-B). Essentially as long as the brain processes keep three independent coordinates they can describe just as much as RGB. Tigraan^{Click here to contact me} 18:22, 4 August 2018 (UTC)