5 ms·

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 yo

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.

dahart 5y ago
I guess I didn’t communicate my points clearly either. I don’t fully buy the hypothesis of the statement that purple is “close” to red. You’re explaining the answer to a question that I’m not convinced is even valid. The first question to answer is: “Is purple close to red?” What does that mean, exactly? Why is this question being asked, what is surprising about purple being close to red? Why aren’t people asking why yellow is close to red? The other point I’m making is that while you’re correct that the left hump is not required logically to explain that a mix of red and blue is close to red, that doesn’t mean you can dismiss it. The human perception of red and blue have a more cyclic connection than between green and blue, precisely because our red response has a bump that overlaps the blue range, and green doesn’t. Physical color does not have a cyclic nature. Short wavelengths do not turn into long wavelengths. Human color perception is perhaps cyclic in a way, but you haven’t defined clearly what you mean by “cyclic”. That’s really my main nit pick with what you’re saying. I agree that most purples are a physical mixture of red and blue wavelengths, or a mixture of red and blue responses. The interesting purple in this discussion is the one that’s not a mixture of wavelengths, but a violet (pure blue) that elicits a mixture of red & blue cone response. That one is due to the red cone’s left hump. Said another way, any so-called “cyclic” connection between red and blue absolutely is increased by the presence of the left hump. Or said a third way, the only reason that the violet in a rainbow is perceived as a mix that is partly red - the only reason your explanation applies here in the first place - is because the left hump exists. If the left hump didn’t exist, then we wouldn’t be perceiving a mix of red and blue, we would be perceiving only blue… and then violet would feel further away from red than it does now. Talking about how monitors display purple does not do a good job of clarifying the questions about purple, that isn’t a good example or analogy, IMO, because monitors cannot represent pure single-wavelength colors, they are three-primary emitters. It’s well known that there are visible colors, shades of violets, blues and reds that RGB monitors cannot display - which I think is very relevant to the question of the perception of purple. The spectra (& luminance) range of monitors is not limited because they cover all perceivable possibilities, they’re limited for more practical reasons of cost and for covering most (but not all) use cases for most (but not all) people.
- robbrown451 5y ago
  "I guess I didn’t communicate my points clearly either. I don’t fully buy the hypothesis of the statement that purple is “close” to red. You’re explaining the answer to a question that I’m not convinced is even valid." Ok, well if you are just rejecting the premise of the article, as well as my premise, I don't know what to tell you. The article simply stated that purple is perceived as closer to red than green is. Do you disagree with that? I've never encountered anyone over the age of 5 that disagrees with that statement. Most people learn that purple is near red in kindergarten. Most people know how color wheels work. Any color wheel shows purple closer to red than green. https://imagesvc.meredithcorp.io/v3/mm/image?url=https%3A%2F%2Fstatic.onecms.io%2Fwp-content%2Fuploads%2Fsites%2F37%2F2020%2F10%2F19%2Fcolor-wheel-db62df1a.jpg https://imagesvc.meredithcorp.io/v3/mm/image?url=https%3A%2F... You can also take the RGB value of purple and find the difference from red (by summing the absolute values of the differences of the red, green and blue values), and do the same with red vs. green. Purple is closer that way as well. Same goes for HSV representations of color, in which hue is represented as degrees of a circle...purple is closer to red than green there as well by any way of doing math on it. Do you reject RGB as a reasonable way to represent color? Do you reject the concept of color wheels? How about the Munsell color solid? Are you familiar with it? https://munsell.com/about-munsell-color/how-color-notation-works/munsell-color-space-and-solid/ https://munsell.com/about-munsell-color/how-color-notation-w... Honestly, it doesn't sound like you want to understand any of this. You're probably not convinced that purple is close to red, and don't know what that means, because you haven't spent much time studying color, thinking about it, or working with it. Have you ever worked with color, in any meaningful way? This is one of many things that I've done: https://www.youtube.com/watch?v=rdh34D1-knk https://www.youtube.com/watch?v=rdh34D1-knk
  - dahart 5y ago
    Using the color wheel to explain why purple is close to red is circular logic. The color wheel is an abstract human construction that places red near purple arbitrarily. The color wheel does not prove that red is fundamentally close to purple. If you’re stuck on color wheels and the kindergarten explanation, then I understand why my questions aren’t making sense to you, and I’m happy to leave it there. I’m not sure why you’re jumping to erroneous conclusions about my background, or why it matters to you. But since you asked, and in the hopes that maybe it could get this conversation back on a productive course, I’ve studied and used color academically and professionally my entire life, including human vision and perception, and computer graphics. I’ve written a few papers with well known color and perception experts on the topic of novel perceptually uniform color spaces, for example. But I wouldn’t say I’m a color or perception expert myself, because the topic is surprisingly deep and tricky, it bears little resemblance to kindergarten knowledge of color wheels. I’ve written high dynamic range spectral renderers in the past, studied spatial and temporal tone mapping, written color conversion code from spectral to CIE XYZ, xyY, Lab, sRGB and other spaces, and like you I’ve written programs and articles about transparency. Premultiplied alpha is one of my favorite topics when it comes to alpha channels. Your JavaScript auto-masking prototype looks really nice. The video didn’t really say much about color, but you may be onto something if you’re pulling your mattes fully automatically. Have you released it or sold it? Since you asked, I’m very familiar with the Munsell space and RGB. RGB has been practical and useful for a long time, but it’s just about one of the worst color spaces there is. This is why people who care about color specify sRGB rather than RGB, and why people who work in CG production and people who make LCD displays don’t use “RGB” anymore. The three biggest problems with RGB are lack of standardization (“RGB” isn’t well defined), RGB is a very perceptually non-uniform color space, and RGB is a crappy and relatively unintuitive space for artists (HSV & HSB are better, but researchers and color UX people have designed much better spaces & pickers for artists). Okay, so, with all that in mind, maybe you’d care to take a more careful stab at explaining why you think purple is “close” to red, and what - exactly - that means?

dahart 5y ago

I guess I didn’t communicate my points clearly either. I don’t fully buy the hypothesis of the statement that purple is “close” to red. You’re explaining the answer to a question that I’m not convinced is even valid. The first question to answer is: “Is purple close to red?” What does that mean, exactly? Why is this question being asked, what is surprising about purple being close to red? Why aren’t people asking why yellow is close to red? The other point I’m making is that while you’re correct that the left hump is not required logically to explain that a mix of red and blue is close to red, that doesn’t mean you can dismiss it. The human perception of red and blue have a more cyclic connection than between green and blue, precisely because our red response has a bump that overlaps the blue range, and green doesn’t. Physical color does not have a cyclic nature. Short wavelengths do not turn into long wavelengths. Human color perception is perhaps cyclic in a way, but you haven’t defined clearly what you mean by “cyclic”. That’s really my main nit pick with what you’re saying. I agree that most purples are a physical mixture of red and blue wavelengths, or a mixture of red and blue responses. The interesting purple in this discussion is the one that’s not a mixture of wavelengths, but a violet (pure blue) that elicits a mixture of red & blue cone response. That one is due to the red cone’s left hump. Said another way, any so-called “cyclic” connection between red and blue absolutely is increased by the presence of the left hump. Or said a third way, the only reason that the violet in a rainbow is perceived as a mix that is partly red - the only reason your explanation applies here in the first place - is because the left hump exists. If the left hump didn’t exist, then we wouldn’t be perceiving a mix of red and blue, we would be perceiving only blue… and then violet would feel further away from red than it does now. Talking about how monitors display purple does not do a good job of clarifying the questions about purple, that isn’t a good example or analogy, IMO, because monitors cannot represent pure single-wavelength colors, they are three-primary emitters. It’s well known that there are visible colors, shades of violets, blues and reds that RGB monitors cannot display - which I think is very relevant to the question of the perception of purple. The spectra (& luminance) range of monitors is not limited because they cover all perceivable possibilities, they’re limited for more practical reasons of cost and for covering most (but not all) use cases for most (but not all) people.

robbrown451 5y ago
"I guess I didn’t communicate my points clearly either. I don’t fully buy the hypothesis of the statement that purple is “close” to red. You’re explaining the answer to a question that I’m not convinced is even valid." Ok, well if you are just rejecting the premise of the article, as well as my premise, I don't know what to tell you. The article simply stated that purple is perceived as closer to red than green is. Do you disagree with that? I've never encountered anyone over the age of 5 that disagrees with that statement. Most people learn that purple is near red in kindergarten. Most people know how color wheels work. Any color wheel shows purple closer to red than green. https://imagesvc.meredithcorp.io/v3/mm/image?url=https%3A%2F%2Fstatic.onecms.io%2Fwp-content%2Fuploads%2Fsites%2F37%2F2020%2F10%2F19%2Fcolor-wheel-db62df1a.jpg https://imagesvc.meredithcorp.io/v3/mm/image?url=https%3A%2F... You can also take the RGB value of purple and find the difference from red (by summing the absolute values of the differences of the red, green and blue values), and do the same with red vs. green. Purple is closer that way as well. Same goes for HSV representations of color, in which hue is represented as degrees of a circle...purple is closer to red than green there as well by any way of doing math on it. Do you reject RGB as a reasonable way to represent color? Do you reject the concept of color wheels? How about the Munsell color solid? Are you familiar with it? https://munsell.com/about-munsell-color/how-color-notation-works/munsell-color-space-and-solid/ https://munsell.com/about-munsell-color/how-color-notation-w... Honestly, it doesn't sound like you want to understand any of this. You're probably not convinced that purple is close to red, and don't know what that means, because you haven't spent much time studying color, thinking about it, or working with it. Have you ever worked with color, in any meaningful way? This is one of many things that I've done: https://www.youtube.com/watch?v=rdh34D1-knk https://www.youtube.com/watch?v=rdh34D1-knk
- dahart 5y ago
  Using the color wheel to explain why purple is close to red is circular logic. The color wheel is an abstract human construction that places red near purple arbitrarily. The color wheel does not prove that red is fundamentally close to purple. If you’re stuck on color wheels and the kindergarten explanation, then I understand why my questions aren’t making sense to you, and I’m happy to leave it there. I’m not sure why you’re jumping to erroneous conclusions about my background, or why it matters to you. But since you asked, and in the hopes that maybe it could get this conversation back on a productive course, I’ve studied and used color academically and professionally my entire life, including human vision and perception, and computer graphics. I’ve written a few papers with well known color and perception experts on the topic of novel perceptually uniform color spaces, for example. But I wouldn’t say I’m a color or perception expert myself, because the topic is surprisingly deep and tricky, it bears little resemblance to kindergarten knowledge of color wheels. I’ve written high dynamic range spectral renderers in the past, studied spatial and temporal tone mapping, written color conversion code from spectral to CIE XYZ, xyY, Lab, sRGB and other spaces, and like you I’ve written programs and articles about transparency. Premultiplied alpha is one of my favorite topics when it comes to alpha channels. Your JavaScript auto-masking prototype looks really nice. The video didn’t really say much about color, but you may be onto something if you’re pulling your mattes fully automatically. Have you released it or sold it? Since you asked, I’m very familiar with the Munsell space and RGB. RGB has been practical and useful for a long time, but it’s just about one of the worst color spaces there is. This is why people who care about color specify sRGB rather than RGB, and why people who work in CG production and people who make LCD displays don’t use “RGB” anymore. The three biggest problems with RGB are lack of standardization (“RGB” isn’t well defined), RGB is a very perceptually non-uniform color space, and RGB is a crappy and relatively unintuitive space for artists (HSV & HSB are better, but researchers and color UX people have designed much better spaces & pickers for artists). Okay, so, with all that in mind, maybe you’d care to take a more careful stab at explaining why you think purple is “close” to red, and what - exactly - that means?