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Author Topic: Why do red-green colorblind people see red and green things as more yellow?  (Read 520 times)

Offline ED1995

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Hello

I don't understand why people with red-green colorblindness see red and green things in a more yellow way. These people have no M cones so the ganglion cells can't be stimulated by M cones and to see yellow there has to be a stimulation of M cones and L cones.

« Last Edit: 19/05/2016 17:46:37 by chris »


 

Offline evan_au

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Quote from: ED1995
These people have no M cones
With a bit of help from Google, I now understand that "M cones" respond to "Medium" wavelengths, and so out of Red (R), Green (G) and Blue(B) light, they respond more strongly to Green light.

Yellow light is intermediate in wavelength between Red and Green , and will normally stimulate both the M (Medium wavelength) and L (Long wavelength) cones.

See: https://en.wikipedia.org/wiki/Cone_cell#Types

Quote
I don't understand why people with red-green colorblindness see red and green things in a more yellow way.
I think it is almost impossible for a person with RGB vision (a "trichromat") to imagine what a person with RB vision (a "dichromat") would see.
Just as it is almost impossible for a person with normal RGB vision to imagine what a R'RGB vision (a "tetrachromat") would see.

The diagram you posted is someone's impression of what is seen, based on tests.

RGB vision and CMYK printing (as used in textbooks) have one more dimension/degree of freedom than RB vision, so there are many ways to map from RB to RGB (or CMYK); and the person with RB vision would confirm that they all look the same to him (or more rarely, her).

I suggest that one way for you to see this effect for yourself is to take a photo with a digital camera (whose R, G & B sensitivity is mapped to human eye spectral sensitivity). Then use a photo processing program that lets you control the R, G & B channels independently. Turn off the G channel.
I expect that this little experiment will map Yellow and Red into Red.
 

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