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> Without the left hump purple would still be purple even if that spectrum would no longer be perceived as purple. Do not quite understand what you're trying t

by Miiko 5y ago

> Without the left hump purple would still be purple even if that spectrum would no longer be perceived as purple. Do not quite understand what you're trying to say (sorry, English is not my native language), here is my understanding - without the left hump purple would be still called "purple" but perceived as kind of deep blue (separate from regular blue, but not closer to red as it is perceived now). Is it what you were saying? > Red and purple are similar since they have many of the same cells getting activated. And this is the part I do not understand - without the left hump, purple (defined as spectral color with shortest wavelength) would NOT activate many red-sensitive (L) cone cells. Why it would have more similarities in cell activation to magenta (defined as red + blue) then? What specifically would cause L-cones input ignored in this case?

robbrown451 5y ago
" without the left hump purple would be still called "purple" but perceived as kind of deep blue (separate from regular blue, but not closer to red as it is perceived now). " That's not correct. Without the left hump, almost everything would appear the same, with a few minor exceptions. You see purple and magenta when both the "red cones" and "blue cones" are activated, but not the "green cones". This can happen two different ways. One is very short wavelengths of light, which appear violet. The red cones are stimulated because of that left hump. This is where violet on the rainbow/spectrum comes from, and why a "black light" looks purplish rather than simply blue. But another way is to have some long wavelengths (which alone would appear red) and some short wavelengths (which alone would appear blue), mixed together. Note that to see a hot pink/magenta/fuchsia, this is the only way it will happen.
- Miiko 5y ago
  You got me confused. In the original comment you wrote: > I disagree with the reasoning that purple looks closer to red than green because of the "left hump" but now you argue: > The red cones are stimulated because of that left hump. So do you agree with similarities of red and purple caused by "left hump" or not?
  - robbrown451 5y ago
    I suggest reading the two links to my posts on Quora, where I go into a good bit of detail about it. But no, the red hump is not why red is close to purple. The red hump is simply why, in some circumstances, you can see purple (technically violet... which is a blueish purple) with only short wavelengths, rather than by mixing long wavelength and short wavelength light. In most cases, when you see something that appears purple, it is because you are seeing a mixture of red (long wavelength) and blue (short wavelength) light. In that case, the left hump is insignificant. Note that in all cases, when you see purple, your "red" cone cells (as well as your "blue" cone cells) are being stimulated. THAT is why red is close to purple.
    - dahart 5y ago
      I was confused and can see why GP was too, this seems to be splitting a very fine hair. But I am trying to read and understand your argument carefully. You reject the left hump theory, but responded by saying purple is triggered by red cone response - which is what the left hump does, assuming the hump exists and is significant. I feel like this argument may be playing loose with terms, and deserves more clarification before announcing disagreement. What does “close” mean when you say red is close to purple, what exactly is “purple”? Violet (pure blue) is a type of purple, as you said, and red-blue mix is also a type of purple, but they aren’t the same. With the right mix, they might be metamers, so the effect of the hump can’t be ignored in the fact that some pure blues might be indistinguishable from some red-blue mixtures. It’s true and I agree with you that seeing most “purple” colors involves seeing some red. But that doesn’t necessarily justify rejecting the left hump theory. You are seeing some red with a 50/50 mix of 400nm and 700nm light. If there’s a left hump, you are also seeing some red with a pure 420nm source. Our perception of blue, and what defines the words “purple” and “violet” to the average human observer includes the experience of seeing purple colors on the blue end of a rainbow, colors that feel similar to the colors on the red end of the rainbow. This fact seems to be at odds with your claim that the left hump of red has nothing at all to do with it, doesn’t it? OTOH, maybe the hump doesn’t exist, and only your explanation is left. What is the source of the cone response function image you posted to Quora? The one on Wikipedia’s entry on cones doesn’t have a left hump. https://en.wikipedia.org/wiki/Cone_cell https://en.wikipedia.org/wiki/Cone_cell Perhaps red being “close” to purple has to do with both of them being at the ends of the perceivable spectrum - both get dark further from green/center. Perhaps it has to do with all color space diagrams of saturated colors always showing blended mixture gradients between the primaries, and not limiting the visualization to mono-wavelength sources - maybe like the number zero and the idea of capitalism - you can’t ever unsee it once you’ve seen it. Perhaps red is not “closer” to purple in any more meaningful sense than any other color mixture of primaries is close to a primary - maybe this whole discussion is only surprise stemming from the discrepancy of graphing colors in two different ways - one is 1-dimensional and the other is 2-dimensional.

by Miiko 5y ago

robbrown451 5y ago

" without the left hump purple would be still called "purple" but perceived as kind of deep blue (separate from regular blue, but not closer to red as it is perceived now). " That's not correct. Without the left hump, almost everything would appear the same, with a few minor exceptions. You see purple and magenta when both the "red cones" and "blue cones" are activated, but not the "green cones". This can happen two different ways. One is very short wavelengths of light, which appear violet. The red cones are stimulated because of that left hump. This is where violet on the rainbow/spectrum comes from, and why a "black light" looks purplish rather than simply blue. But another way is to have some long wavelengths (which alone would appear red) and some short wavelengths (which alone would appear blue), mixed together. Note that to see a hot pink/magenta/fuchsia, this is the only way it will happen.

Miiko 5y ago
You got me confused. In the original comment you wrote: > I disagree with the reasoning that purple looks closer to red than green because of the "left hump" but now you argue: > The red cones are stimulated because of that left hump. So do you agree with similarities of red and purple caused by "left hump" or not?
- robbrown451 5y ago
  I suggest reading the two links to my posts on Quora, where I go into a good bit of detail about it. But no, the red hump is not why red is close to purple. The red hump is simply why, in some circumstances, you can see purple (technically violet... which is a blueish purple) with only short wavelengths, rather than by mixing long wavelength and short wavelength light. In most cases, when you see something that appears purple, it is because you are seeing a mixture of red (long wavelength) and blue (short wavelength) light. In that case, the left hump is insignificant. Note that in all cases, when you see purple, your "red" cone cells (as well as your "blue" cone cells) are being stimulated. THAT is why red is close to purple.
  - dahart 5y ago
    I was confused and can see why GP was too, this seems to be splitting a very fine hair. But I am trying to read and understand your argument carefully. You reject the left hump theory, but responded by saying purple is triggered by red cone response - which is what the left hump does, assuming the hump exists and is significant. I feel like this argument may be playing loose with terms, and deserves more clarification before announcing disagreement. What does “close” mean when you say red is close to purple, what exactly is “purple”? Violet (pure blue) is a type of purple, as you said, and red-blue mix is also a type of purple, but they aren’t the same. With the right mix, they might be metamers, so the effect of the hump can’t be ignored in the fact that some pure blues might be indistinguishable from some red-blue mixtures. It’s true and I agree with you that seeing most “purple” colors involves seeing some red. But that doesn’t necessarily justify rejecting the left hump theory. You are seeing some red with a 50/50 mix of 400nm and 700nm light. If there’s a left hump, you are also seeing some red with a pure 420nm source. Our perception of blue, and what defines the words “purple” and “violet” to the average human observer includes the experience of seeing purple colors on the blue end of a rainbow, colors that feel similar to the colors on the red end of the rainbow. This fact seems to be at odds with your claim that the left hump of red has nothing at all to do with it, doesn’t it? OTOH, maybe the hump doesn’t exist, and only your explanation is left. What is the source of the cone response function image you posted to Quora? The one on Wikipedia’s entry on cones doesn’t have a left hump. https://en.wikipedia.org/wiki/Cone_cell https://en.wikipedia.org/wiki/Cone_cell Perhaps red being “close” to purple has to do with both of them being at the ends of the perceivable spectrum - both get dark further from green/center. Perhaps it has to do with all color space diagrams of saturated colors always showing blended mixture gradients between the primaries, and not limiting the visualization to mono-wavelength sources - maybe like the number zero and the idea of capitalism - you can’t ever unsee it once you’ve seen it. Perhaps red is not “closer” to purple in any more meaningful sense than any other color mixture of primaries is close to a primary - maybe this whole discussion is only surprise stemming from the discrepancy of graphing colors in two different ways - one is 1-dimensional and the other is 2-dimensional.