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Thank you for the explanation. That was highly interesting. Does anyone else know if the human eye does perceive color directly? Is this at all technically poss

by kharak 6y ago

Thank you for the explanation. That was highly interesting. Does anyone else know if the human eye does perceive color directly? Is this at all technically possible? And if yes, why aren't we doing it with cameras?

natosaichek 6y ago
What do you mean by "directly"? Color is a human abstraction over the reception intensity of certain wavelengths of light.
- Koshkin 6y ago
  What do you mean “abstraction”? The colors that I am seeing look very concrete to me. (Also, the “wavelength theory” of color perception does not explain why TV screens work.)
  - natosaichek 6y ago
    The human retina is composed of cells that are responsive to different wavelengths of light. Color is the word that we use to describe the subjective sensations associated with certain patterns of stimulation of those cells. There is no "yellowness" in a bananna. We cannot construct an instrument capable of measuring "yellow" as such. What we can measure are the intensities of wavelengths of light. We can notice that when people say they perceive "yellow" that the spectral intensity graph has certain patterns. This is the physical phenomenon that produces the sensation of "yellow." Humans are not good at judging reality introspectively. We experience everything heavily filtered through a variety of lenses. Our feeling that color is "concrete" is not predictive or explanatory... we cannot build mechanisms based on it. The idea that our perception of color is a result of interactions between certain wavelengths of light and certain photosensitive tissues in our eyes is both predictive and explanatory. We can design systems that have similar types of wavelength intensity sensitivity components and measure the physical response of those systems. That's how cameras work. We can reverse the process and take those measured wavelength intensities and re-emit them from variable-wavelength light sources and produce images. That's how you're reading what I've typed right now - the images produced by the display you're looking at were generated in this fashion. I'm not sure what you mean by the “wavelength theory” of color perception.
    - Koshkin 6y ago
      > We cannot construct an instrument capable of measuring "yellow" as such. Of course we can. We can capture the signal sent through the optical nerve and then reproduce it as a stimulus which will make the brain “see” yellow color. Besides, humans are capable of distinguishing literally millions of colors, of which just a tiny fraction can be attributed to measuring particular wavelengths (or, more accurately, particular energies of the incident photons). In that way the eye is different from the ear (which performs a kind of Fourier analysis of the sound wave).
      - natosaichek 6y ago
        Well, the instrument wouldn't me measuring yellowness... it would be measuring electrical impulses that (in some individuals) correspond to the (verbally asserted) perception of "yellow". "Yellow" is not a characteristic of the world; it's a convenient label that humans apply to some bucketed sets of sensory perceptions. I agree that there are sensory perceptions humans are capable of perceiving and labeling as colors that cannot be attributed to external physical phenomena, but those are largely artifacts of the way our brain processes signals. For example if you stare at a purple dot for some time, then look away, you'll perceive a yellow dot where there is no external set of photons corresponding to the wavelengths that normally trigger the sensation of yellow striking your retina. This is just more explanation about how "yellowness" is a characteristic of our brains, not of the external world. Or did you mean something other than what I'm referring to here? I think that for the vast bulk of humans, the vast bulk of the colors they perceive regularly are due to photons striking rods and cones in their eyes at various intensities, causing color sensations to occur in the brain. Do you think something else is happening? You seem to understand how the eye works, and some neuroscience, so I don't understand how you can have the questions that you raise about whether we can build cameras that sense "color" instead of "light"
zinekeller 6y ago
Short answer: No. We (the majority anyway, as some are colourblind) only perceive lightness, reddish, greenish, and bluish. The brain uses the info and effectively synthesises the image in our brains. Long answer: Colour is a very rabbithole topic but Captain Disillusion has a summary of it (https://youtu.be/FTKP0Y9MVus https://youtu.be/FTKP0Y9MVus) and Technology Connections has a discussion (https://youtu.be/uYbdx4I7STg https://youtu.be/uYbdx4I7STg).
ddingus 6y ago
I believe in purple. After you get done exploring how we perceive colors associated with different wave lengths of light, and how nobody really knows whether these are common somehow, or unique to each of us, that sentence should bring you both a chuckle and some wonder about perception.
- Koshkin 6y ago
  From the physiological standpoint human individuals are far, far from being unique. The electrochemical reaction of a neuron in the cortex which indicates the perception of ‘red’ is pretty much the same in any human (and not only).
  - ddingus 6y ago
    Whether that subjective perception is the same remains unknown. We have no solid way to communicate any of that yet. I am inclined to believe it is, but we do not really know.
nwallin 6y ago
...it's complicated. Very complicated. However complicated you think it is, it's more complicated than that. Please note that I'm not an expert in human eyeball physiology, I'm just a computer programmer who's tried pretty hard to come to a better understanding of how to make computer vision better. (I've failed, fyi. Caveat emptor.) The human eye has four basic cell types, rod cells and cone cells, and there are three subtypes of cones, short, medium, and long. The three subtypes of cone cells sense blue, green, and red light more or less directly. Medium and long cone cells, which directly detect green and red light, almost entirely overlap. [0] It is more accurate to say that long cone cells detect yellow light than it is to say it detects red light. There is a brain system which measures the difference in response between the long (red) and medium (green) cells and uses the difference to say "aha! this must be red!" The ratio of short (blue) medium (green) and long (red (yellow)) cone cells are roughly 2%, 2/3, and 1/3. The cells in your eye which detect blue light are more or less a rounding error. The cells which detect green light are roughly twice as numerous as the cells which detect red (well, yellow) light. If you see a thing and think, "man, that's awfully blue," it's not because your eyes are telling you "hey, this thing is awfully blue". The "blue" signal is barely noticeable in the overall signal; but your brain jacks up its responsiveness to the minuscule blue signal. One of the side effects of the completely fucked ratios between the three types of cones is that your perception of the overall brightness of a thing is mostly down to how green it is. This shows up in lots of standards; NTSC, JPEG, the whole nine yards. If you've ever implemented a conversion between RGB and any luminosity-chroma colorspace (YUV, YCbCr, YIQ, NTSC, any of them) there's a moment where you'll go "wait a minute this doesn't make any fucking sense". You look at the numbers and the luminosity channel is just... green, and you know that the other two chroma channels are quartered in resolution. And you'll think that makes no sense. But that's how it works. Then you'll remember that color sensors have their pixels arranged in groups of four, with two green, one red, and one blue channel. There must be some green conspiracy. And there is. It's your brain. It's your eyeballs with 2/3 of its cone cells being green sensitive ones. Those are your cone cells. Rod cells are entirely different. It's trivial to say well, cone cells see color, rod cells see black and white, but it's more complicated than that. Rod cells are excellent in low light conditions, cone cells not so much. Cone cells see motion very well, rod cells not so much. Cone cells can discern fine detail, rod cells do not. Rods and cones are not evenly distributed across the retina either; cone cells are densely packed in the center, rod cells are more common in peripheral vision. Look at a colorful thing directly; take a note of how colorful it is. Now look away from it, so it's only in your peripheral vision; take a note of how colorful it is. Does it seem just as colorful? It isn't. That's your brain fucking with you. Your brain knows it's in your peripheral vision and all the colors are muted out there, so your brain exaggerates the colorfulness. Cone cells are 30 times as dense in the center of your vision as they are just outside the center of your vision. [1] That's why you can read a word directly where you're looking but it's very difficult to read elsewhere. The reality is that your retinas give a fucking mess of bullshit to your brain, and the brain is the most incredible image processing system conceivable. It takes bullshit that makes no damn sense and -- holy shit I forgot to talk about blind spots. Ok, so your rods and cones have a light sensitive thing, with a wire in the back, and all the wires get bundled up in the optic nerve that goes to the brain. Here's the thing: they're fucking plugged in backwards. The wires go forward, and are bundled up between your retinas and the stuff you're looking at. The big fat optic nerve therefore constitutes a large chunk of your vision where you can't see anything. Your brain just.. invents stuff where the optic nerve burrows through your retina. Other weird stuff. If it's bright, the rods and cones send no signal, if it's dark, they send a strong signal. It's inverted. There's apparently a very good reason for this but I don't remember what it is. Also, the rods continuously produce a light sensitive substance that amplifies the light sensitivity but is destroyed in the process. It takes a long time to build up a reserve. This is why it takes time to "build up" your dark vision, and why it's so easily destroyed by lighting a cigarette. The physiology of "ow it's bright" as opposed to "it's bright" isn't just on your retinas, it's also on your eyelids and your iris, but more importantly, it's shared between your two eyes. This is why closing one eye makes it less painful when you go from a dark place to a bright place. The point is, the study of human vision is not the study of the human eye. The study of human vision is the study of the human brain. Much of what we do with color spaces and image compression is dictated by our stupid smart eyeballs and our stupid smart brains. Video codecs compress with 4:2:0 chroma subsampling because the brain's gonna decompress that shit better than a computer can anyway. Cameras have twice as many green sensitive pixels as blur or red pixels because the eye resolution is much sharper in green than other colors. More advanced image and video compression schemes will try harder to account for human eye-brain physiology. [0] https://upload.wikimedia.org/wikipedia/commons/0/04/Cone-fundamentals-with-srgb-spectrum.svg https://upload.wikimedia.org/wikipedia/commons/0/04/Cone-fun... [1] https://upload.wikimedia.org/wikipedia/commons/3/3c/Human_photoreceptor_distribution.svg https://upload.wikimedia.org/wikipedia/commons/3/3c/Human_ph...

by kharak 6y ago

natosaichek 6y ago

What do you mean by "directly"? Color is a human abstraction over the reception intensity of certain wavelengths of light.

Koshkin 6y ago
What do you mean “abstraction”? The colors that I am seeing look very concrete to me. (Also, the “wavelength theory” of color perception does not explain why TV screens work.)
- natosaichek 6y ago
  The human retina is composed of cells that are responsive to different wavelengths of light. Color is the word that we use to describe the subjective sensations associated with certain patterns of stimulation of those cells. There is no "yellowness" in a bananna. We cannot construct an instrument capable of measuring "yellow" as such. What we can measure are the intensities of wavelengths of light. We can notice that when people say they perceive "yellow" that the spectral intensity graph has certain patterns. This is the physical phenomenon that produces the sensation of "yellow." Humans are not good at judging reality introspectively. We experience everything heavily filtered through a variety of lenses. Our feeling that color is "concrete" is not predictive or explanatory... we cannot build mechanisms based on it. The idea that our perception of color is a result of interactions between certain wavelengths of light and certain photosensitive tissues in our eyes is both predictive and explanatory. We can design systems that have similar types of wavelength intensity sensitivity components and measure the physical response of those systems. That's how cameras work. We can reverse the process and take those measured wavelength intensities and re-emit them from variable-wavelength light sources and produce images. That's how you're reading what I've typed right now - the images produced by the display you're looking at were generated in this fashion. I'm not sure what you mean by the “wavelength theory” of color perception.
  - Koshkin 6y ago
    > We cannot construct an instrument capable of measuring "yellow" as such. Of course we can. We can capture the signal sent through the optical nerve and then reproduce it as a stimulus which will make the brain “see” yellow color. Besides, humans are capable of distinguishing literally millions of colors, of which just a tiny fraction can be attributed to measuring particular wavelengths (or, more accurately, particular energies of the incident photons). In that way the eye is different from the ear (which performs a kind of Fourier analysis of the sound wave).
    - natosaichek 6y ago
      Well, the instrument wouldn't me measuring yellowness... it would be measuring electrical impulses that (in some individuals) correspond to the (verbally asserted) perception of "yellow". "Yellow" is not a characteristic of the world; it's a convenient label that humans apply to some bucketed sets of sensory perceptions. I agree that there are sensory perceptions humans are capable of perceiving and labeling as colors that cannot be attributed to external physical phenomena, but those are largely artifacts of the way our brain processes signals. For example if you stare at a purple dot for some time, then look away, you'll perceive a yellow dot where there is no external set of photons corresponding to the wavelengths that normally trigger the sensation of yellow striking your retina. This is just more explanation about how "yellowness" is a characteristic of our brains, not of the external world. Or did you mean something other than what I'm referring to here? I think that for the vast bulk of humans, the vast bulk of the colors they perceive regularly are due to photons striking rods and cones in their eyes at various intensities, causing color sensations to occur in the brain. Do you think something else is happening? You seem to understand how the eye works, and some neuroscience, so I don't understand how you can have the questions that you raise about whether we can build cameras that sense "color" instead of "light"

zinekeller 6y ago

Short answer: No. We (the majority anyway, as some are colourblind) only perceive lightness, reddish, greenish, and bluish. The brain uses the info and effectively synthesises the image in our brains. Long answer: Colour is a very rabbithole topic but Captain Disillusion has a summary of it (https://youtu.be/FTKP0Y9MVus https://youtu.be/FTKP0Y9MVus) and Technology Connections has a discussion (https://youtu.be/uYbdx4I7STg https://youtu.be/uYbdx4I7STg).

ddingus 6y ago

I believe in purple. After you get done exploring how we perceive colors associated with different wave lengths of light, and how nobody really knows whether these are common somehow, or unique to each of us, that sentence should bring you both a chuckle and some wonder about perception.

Koshkin 6y ago
From the physiological standpoint human individuals are far, far from being unique. The electrochemical reaction of a neuron in the cortex which indicates the perception of ‘red’ is pretty much the same in any human (and not only).
- ddingus 6y ago
  Whether that subjective perception is the same remains unknown. We have no solid way to communicate any of that yet. I am inclined to believe it is, but we do not really know.

nwallin 6y ago

...it's complicated. Very complicated. However complicated you think it is, it's more complicated than that. Please note that I'm not an expert in human eyeball physiology, I'm just a computer programmer who's tried pretty hard to come to a better understanding of how to make computer vision better. (I've failed, fyi. Caveat emptor.) The human eye has four basic cell types, rod cells and cone cells, and there are three subtypes of cones, short, medium, and long. The three subtypes of cone cells sense blue, green, and red light more or less directly. Medium and long cone cells, which directly detect green and red light, almost entirely overlap. [0] It is more accurate to say that long cone cells detect yellow light than it is to say it detects red light. There is a brain system which measures the difference in response between the long (red) and medium (green) cells and uses the difference to say "aha! this must be red!" The ratio of short (blue) medium (green) and long (red (yellow)) cone cells are roughly 2%, 2/3, and 1/3. The cells in your eye which detect blue light are more or less a rounding error. The cells which detect green light are roughly twice as numerous as the cells which detect red (well, yellow) light. If you see a thing and think, "man, that's awfully blue," it's not because your eyes are telling you "hey, this thing is awfully blue". The "blue" signal is barely noticeable in the overall signal; but your brain jacks up its responsiveness to the minuscule blue signal. One of the side effects of the completely fucked ratios between the three types of cones is that your perception of the overall brightness of a thing is mostly down to how green it is. This shows up in lots of standards; NTSC, JPEG, the whole nine yards. If you've ever implemented a conversion between RGB and any luminosity-chroma colorspace (YUV, YCbCr, YIQ, NTSC, any of them) there's a moment where you'll go "wait a minute this doesn't make any fucking sense". You look at the numbers and the luminosity channel is just... green, and you know that the other two chroma channels are quartered in resolution. And you'll think that makes no sense. But that's how it works. Then you'll remember that color sensors have their pixels arranged in groups of four, with two green, one red, and one blue channel. There must be some green conspiracy. And there is. It's your brain. It's your eyeballs with 2/3 of its cone cells being green sensitive ones. Those are your cone cells. Rod cells are entirely different. It's trivial to say well, cone cells see color, rod cells see black and white, but it's more complicated than that. Rod cells are excellent in low light conditions, cone cells not so much. Cone cells see motion very well, rod cells not so much. Cone cells can discern fine detail, rod cells do not. Rods and cones are not evenly distributed across the retina either; cone cells are densely packed in the center, rod cells are more common in peripheral vision. Look at a colorful thing directly; take a note of how colorful it is. Now look away from it, so it's only in your peripheral vision; take a note of how colorful it is. Does it seem just as colorful? It isn't. That's your brain fucking with you. Your brain knows it's in your peripheral vision and all the colors are muted out there, so your brain exaggerates the colorfulness. Cone cells are 30 times as dense in the center of your vision as they are just outside the center of your vision. [1] That's why you can read a word directly where you're looking but it's very difficult to read elsewhere. The reality is that your retinas give a fucking mess of bullshit to your brain, and the brain is the most incredible image processing system conceivable. It takes bullshit that makes no damn sense and -- holy shit I forgot to talk about blind spots. Ok, so your rods and cones have a light sensitive thing, with a wire in the back, and all the wires get bundled up in the optic nerve that goes to the brain. Here's the thing: they're fucking plugged in backwards. The wires go forward, and are bundled up between your retinas and the stuff you're looking at. The big fat optic nerve therefore constitutes a large chunk of your vision where you can't see anything. Your brain just.. invents stuff where the optic nerve burrows through your retina. Other weird stuff. If it's bright, the rods and cones send no signal, if it's dark, they send a strong signal. It's inverted. There's apparently a very good reason for this but I don't remember what it is. Also, the rods continuously produce a light sensitive substance that amplifies the light sensitivity but is destroyed in the process. It takes a long time to build up a reserve. This is why it takes time to "build up" your dark vision, and why it's so easily destroyed by lighting a cigarette. The physiology of "ow it's bright" as opposed to "it's bright" isn't just on your retinas, it's also on your eyelids and your iris, but more importantly, it's shared between your two eyes. This is why closing one eye makes it less painful when you go from a dark place to a bright place. The point is, the study of human vision is not the study of the human eye. The study of human vision is the study of the human brain. Much of what we do with color spaces and image compression is dictated by our stupid smart eyeballs and our stupid smart brains. Video codecs compress with 4:2:0 chroma subsampling because the brain's gonna decompress that shit better than a computer can anyway. Cameras have twice as many green sensitive pixels as blur or red pixels because the eye resolution is much sharper in green than other colors. More advanced image and video compression schemes will try harder to account for human eye-brain physiology. [0] https://upload.wikimedia.org/wikipedia/commons/0/04/Cone-fundamentals-with-srgb-spectrum.svg https://upload.wikimedia.org/wikipedia/commons/0/04/Cone-fun... [1] https://upload.wikimedia.org/wikipedia/commons/3/3c/Human_photoreceptor_distribution.svg https://upload.wikimedia.org/wikipedia/commons/3/3c/Human_ph...