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I came across this paper Color defect and color theory. The paper explained about how unilateral color blind (people who color blind only in 1 eye) actually see less bright in their color-blind eye (in graph : filled bullet) compared to the normal eye (in graph : white bullet). Especially to the scene that corresponds to the missing cone (in this paper, Deuteranopes. Missing cones = green)

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I have 2 questions regarding this brightness loss in color blind people.

  1. Green cones response are near the red cones response, and they are overlapping. How is it possible that Deuteranopes loss brightness in Green and Blue (which will make more sense if they also loss brightness in Red, thus loss brightness in the whole spectrum) but instead, still achieve the same amount of brightness in Red ? Despite Red and Green color-blind have the same color combination possibility (gamut mapping) that they can perceive ?

  2. Could it be that color-blind people have stronger sensitivity in other cones (for example : stronger in red) and then this red opsin actually replace / fill the missing cones stimuli in retina, so their retina still able to perceive the same amount of brightness on that excessive cones ?

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Kudos for Delta-S in Reddit for enlighten me. Original post is here.

The answer is no, color blind people don't have stronger sensitivity in their other remaining cones. This goes back to the Photopic Sensitivity Graph below.

As you can see, human vision are most sensitive to green. All responses of green cone are within the photopic sensitivity as well as most response of the red cones. And despite few responses of red cones are outside the Photopic sensitivity, the peak sensitivity of red cones is very close to the peak of Photopic sensitivity (560nm and 555nm).

enter image description here

  • Peak Photopic Sensitivity: 555nm
  • S cones peak : 420nm
  • M cones peak : 530nm
  • L cones peak : 560nm

So, in case of Deuteranopic, depending on which wavelength is loss (defected) from their eye, if it closer to the red response then they will likely to experience luminance loss as well. However, if the green cone that is defected is far from the red response, the red cones still have possibility to maintain the luminance they can achieve.

Unfortunately in the paper, it's not mentioned which sensitivity wavelength was defected from the unilateral participant. It is only mentioned "result indicate that she was deuteranopic".

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