4 ms·

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"

by 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.
  - Miiko 5y ago
    Apparently, the diagram on Wikipedia page is not correct (either outdated or oversimplified). According to what I could google, the research does show a hump in L-cones sensitivity at violet colors, for example: https://www.yorku.ca/eye/specsens.htm https://www.yorku.ca/eye/specsens.htm https://www.researchgate.net/figure/Normalized-spectral-sensitivity-of-retinal-rod-and-cone-cells_fig7_265155524 https://www.researchgate.net/figure/Normalized-spectral-sens...
    - dahart 5y ago
      I think the Wikipedia page is correct, along with the comment above about this being CIE color matching functions. https://news.ycombinator.com/item?id=28651997 https://news.ycombinator.com/item?id=28651997 The CIE color matching functions are a very interesting topic, and a subtle distinction between cone response and perceived ability to match a given color. The main issue being that we haven’t had any ways until recently to directly measure cone response. The color matching functions are derived from clever experiments that attempt to figure out cone response based on what humans think they see, without opening their heads. This article also has a decent introductory explanation of the color matching functions and where the left hump comes from. https://medium.com/hipster-color-science/a-beginners-guide-to-colorimetry-401f1830b65a https://medium.com/hipster-color-science/a-beginners-guide-t...
  - robbrown451 5y ago
    Look at it this way. Imagine you are using a paint program, and want a purple, magenta, or violet. Maybe you are drawing a rainbow, and want that violet that you see when you see a rainbow in real life. How does the monitor represent that? By somehow generating a very short wavelength of light, that appears purplish? No of course not... it does it by lighting up both the blue subpixels, and the red subpixels. There are no violet subpixels.... that would be a waste of money to make a monitor that actually emits that wavelength as a separate subpixel. Your eyes don't care... they see it as purple. Another thing that could help you understand this is by looking at how yellow works. Yellow can be formed by a single wavelength of "yellow light", such as a yellow laser. But it can also be formed by mixing pure red and pure green light. Again, your eyes don't care, it is yellow either way. (in most real world situations, such as a typical yellow reflective object, it is formed by a whole range of wavelengths ranging from red to green). You are making this more complicated than it needs to be. Basic color theory, including the cyclic nature and the way purple is between red and blue, does not need the "left hump" for it to work. You should try to understand how RGB works first, then later learn how the quirks of the human visual system affect it. Another interesting thing is that the peak sensitivity of the "red cones" is actually in the yellowish green area of the spectrum, but our brain does some post processing, so to speak, to make it so we can perceive actual red. I don't know where I got the image of the chart, you can reverse image search it. Not sure why the left hump is not shown on the one on wikipedia.
- Miiko 5y ago
  Ok, think I got it, the confusion is how we define "purple". Yes, if we define it as "magenta" = mixture of red and blue, then it is pretty obvious that it would be closer to red than green and, of course, the left hump is insignificant. However, in the TFA, it is defined as "purple is at the opposite end of the spectrum from red" (which is technically "violet" indeed), and in that case purple being close to red (by being perceived same as magenta) can only be explained by "red hump" = red-sensitive (L) cones being also sensitive to blue. Does not look you disagree with that.

by Miiko 5y ago

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.
- Miiko 5y ago
  Apparently, the diagram on Wikipedia page is not correct (either outdated or oversimplified). According to what I could google, the research does show a hump in L-cones sensitivity at violet colors, for example: https://www.yorku.ca/eye/specsens.htm https://www.yorku.ca/eye/specsens.htm https://www.researchgate.net/figure/Normalized-spectral-sensitivity-of-retinal-rod-and-cone-cells_fig7_265155524 https://www.researchgate.net/figure/Normalized-spectral-sens...
  - dahart 5y ago
    I think the Wikipedia page is correct, along with the comment above about this being CIE color matching functions. https://news.ycombinator.com/item?id=28651997 https://news.ycombinator.com/item?id=28651997 The CIE color matching functions are a very interesting topic, and a subtle distinction between cone response and perceived ability to match a given color. The main issue being that we haven’t had any ways until recently to directly measure cone response. The color matching functions are derived from clever experiments that attempt to figure out cone response based on what humans think they see, without opening their heads. This article also has a decent introductory explanation of the color matching functions and where the left hump comes from. https://medium.com/hipster-color-science/a-beginners-guide-to-colorimetry-401f1830b65a https://medium.com/hipster-color-science/a-beginners-guide-t...
- robbrown451 5y ago
  Look at it this way. Imagine you are using a paint program, and want a purple, magenta, or violet. Maybe you are drawing a rainbow, and want that violet that you see when you see a rainbow in real life. How does the monitor represent that? By somehow generating a very short wavelength of light, that appears purplish? No of course not... it does it by lighting up both the blue subpixels, and the red subpixels. There are no violet subpixels.... that would be a waste of money to make a monitor that actually emits that wavelength as a separate subpixel. Your eyes don't care... they see it as purple. Another thing that could help you understand this is by looking at how yellow works. Yellow can be formed by a single wavelength of "yellow light", such as a yellow laser. But it can also be formed by mixing pure red and pure green light. Again, your eyes don't care, it is yellow either way. (in most real world situations, such as a typical yellow reflective object, it is formed by a whole range of wavelengths ranging from red to green). You are making this more complicated than it needs to be. Basic color theory, including the cyclic nature and the way purple is between red and blue, does not need the "left hump" for it to work. You should try to understand how RGB works first, then later learn how the quirks of the human visual system affect it. Another interesting thing is that the peak sensitivity of the "red cones" is actually in the yellowish green area of the spectrum, but our brain does some post processing, so to speak, to make it so we can perceive actual red. I don't know where I got the image of the chart, you can reverse image search it. Not sure why the left hump is not shown on the one on wikipedia.
Miiko 5y ago
Ok, think I got it, the confusion is how we define "purple". Yes, if we define it as "magenta" = mixture of red and blue, then it is pretty obvious that it would be closer to red than green and, of course, the left hump is insignificant. However, in the TFA, it is defined as "purple is at the opposite end of the spectrum from red" (which is technically "violet" indeed), and in that case purple being close to red (by being perceived same as magenta) can only be explained by "red hump" = red-sensitive (L) cones being also sensitive to blue. Does not look you disagree with that.