How can RGB reproduce all (most) colours?

  • Context: Undergrad 
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Discussion Overview

The discussion revolves around the ability of RGB color models to reproduce a wide range of colors, focusing on the physics and physiology behind color perception. Participants explore how specific frequencies of red, green, and blue light can combine to create other colors, such as yellow, and the relationship between these colors and the human visual system.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how RGB frequencies can produce colors different from themselves, such as yellow.
  • Another participant suggests that the explanation lies in the physiology of the eye, noting that there are three types of color receptors with response spectra centered on red, green, and blue.
  • A participant mentions that pure wavelengths produce varying responses across all three types of receptors, allowing the brain to distinguish thousands of colors.
  • There is a reference to the idea that white light can be seen as a combination of RGB, likening it to white noise.
  • One participant points out that the sensitivity peaks of the receptors are not exactly aligned with pure red, green, and blue wavelengths.
  • A comparison is made between the RGB representation of orange and the actual color of orange skin, highlighting the limitations of the RGB gamut.

Areas of Agreement / Disagreement

Participants generally agree that the physiology of the eye plays a significant role in color perception, but there is no consensus on the specifics of how RGB can reproduce all colors or the implications of the limitations of the RGB gamut.

Contextual Notes

There are unresolved questions regarding the exact mechanisms by which RGB light combines to create other colors and how this relates to the response of the eye's receptors. The discussion also touches on the limitations of the RGB color model in representing certain colors accurately.

jodyflorian
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Hiya,

While learning about photography I've realized that there's something I can't explain with the physics I was taught at school.

What I do know is that pure red, green and blue have specific frequencies. And that combining the colours produces white. And although I don't know exactly why, I've read that red, green and blue together can approximate most colours - it has a limited "gamut" although personally I can't spot the deficiency.

My main questions are...
1) How can those frequencies produce colours at frequencies different to themselves? e.g. yellow
2) And I thought white was the visual equivalent of white noise (broad band) so how can that be produced with RGB?

Has it got anything to do with how the receptors in our eyes work? Back to biology now lol I remember there existing RGB sensitive cells... it's sounding less and less like a coincidence! Does that mean a green receptor would react to frequencies on either side? Just guessing now...
 
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Your 3 is right, it has everything to do with receptors. IOW it is a question of physiology not physics.

Just rough principle since I think the explanation is here on this site somewhere in more detail and very many textbooks, you have 3 types of receptors with response spectra spread but centred on R G or B. Some pure wavelength you ask about will produce a given response on all 3, proportions different according to that wavelength. So each pure wavelength corresponds to a unique combination for you neural biocomputer amd it distinguishes thousands of them.
 
Sorry for the physiology post :p

Thanks - now I know what to look into next :)
 
Wiki has a reasonable article. The 3 sets of receptors on most human eyes, each with maximum sensitivity at some frequency, but the sensitivity peaks are not "exactly" red, blue, and green.

http://en.wikipedia.org/wiki/Color
 
jodyflorian said:
it has a limited "gamut" although personally I can't spot the deficiency.

Compare the "orange" patch in wikipedia's article (The colors of the visible light spectrum), which is (R=255, V=128, B=0) and has a 100% saturation, to the color of an orange skin or a clementine skin !
 

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