3 ms·

The retina itself does various forms of processing, some of which is about eliminating noise, but some of which is involved in relatively complex things like ed

The retina itself does various forms of processing, some of which is about eliminating noise, but some of which is involved in relatively complex things like edge detection. The nerve bundles connected to the retina do further processing. The visual cortex itself does a lot of processing, then the conscious part of the brain does even more. There's recompositing and temporal correlation, motion-compensation, prediction, edge detection, lighting/shadow compensation & color perception, threat assessment, pattern recognition, object recognition, face recognition and that's just scratching the surface. Even transmission of color information isn't a simple RBG signal. It appears the eye transmits differential signals (such as B-Y) and other information as well. There are multiple layers of processing that go on in our visual system. You can't reduce it to three axes. The eye is not a camera, doesn't work like a camera, and can't be simplistically thought of as if it were a camera.

tbabb 9y ago
All of those things about visual processing are true. > You can't reduce it to three axes. This is my claim: It is possible to represent all possible visual stimulus with: f(direction, time) -> (a, b, c). That is what I mean by "vision is three dimensional". It is not possible to add another channel "d" to the (a,b,c) tuple which is not redundant; so anything you add would not be an extra axis or increase the dimensionality of the perception space. The brain/retina may generate lots of extra "channels" from processing this (moving) three-valued image, but those extra channels can't be stimulated independently of each other; they depend entirely on those original three degrees of freedom as a function of space and time. In that sense they aren't really "axes", because they aren't degrees of freedom. That's what I mean by "there isn't an extra channel." If you agree with that, then we don't disagree and we are just arguing semantics. :)
- edejong 9y ago
  It’s funny that you introduce time in your equation, because it shows how your view is incomplete. In our visual system, you cannot reduce to three dimensions without creating a recursive relation. It should be more like: Ret(a,b,c)_t = f(Ret(a,b,c)_{t-1}, current_stimulus) Since it is a recurrence, we cannot reduce to three dimensions.
- shawnz 9y ago
  Couldn't you use this same line of thinking to argue that only one dimension is required? Our eyes may generate 3 channels, but don't they depend entirely on the frequency of light received which is one dimensional?
  - krallja 9y ago
    Light is not perceived at a single frequency. It is a spectrum. That’s why you can see non-spectral colors like pink.
    - shawnz 9y ago
      OK, well, are there any colours which are not representable with two frequencies? That is still less than three dimensions.
      - krallja 9y ago
        White.
        shawnz 9y ago
        Isn't that representable with a mixture of blue and yellow light?
        tbabb 9y ago
        You can pick a blue and a yellow and a proportion at which to mix them which will produce white, but for any two primaries you pick, there are a multitude of colors you can't represent. For example, if your basis is blue-yellow as you suggest, then you can't represent red or green (and an infinity of other colors off-axis). Fundamentally the chromaticity diagram[1] is 2D (with a third axis for intensity). You need to mix at least three points to span the space of the plane. [1] https://dotcolordotcom.files.wordpress.com/2012/08/anatomy-of-a-cie-diagram2x.png https://dotcolordotcom.files.wordpress.com/2012/08/anatomy-o...
- Balgair 9y ago
  To be fair, the receptors are VERY time dependent too. Take a stare at the top bar for ~20 seconds and then move your eyes down just a bit. You'll see an echo image of the opposite color (colorblindness depending). This shows that even a 'little' time spent saturating the retina will effect the later images. As other people mention, the retina does a LOT of pre-processing before any 'signal' gets sent. The very first synapse from the receptor is heavily modified by horizontal and bipolar cells in a time-dependent reactive manner. The 'images' we 'see' are nothing like what the retina 'sees'. People with cataracts will commonly have very advanced occlusions before thinking there may be a problem, due to the incredible amount of processing the retina itself does. They really cannot 'see' that they cannot 'see'. So, trying to reduce vision to a color mapping is just so ... computational. Biology is not like that all the time. It's not a 'map' like with sound and hearing (where tonotopy is semi-conserved throughout brain processing). With vision, things are used as 'information' almost instantly, but for certain by the end of the LGN into V1. You can't really backtrack the data through the system once it hit V1, it self-modifies the memristance of the synapses too quickly to chase the action potentials again. So thinking of things as 'red' isn't what the brain wants to do, it's not matrix algebra. It's 'grandmother' and 'tiger' and 'that-look-in-her-eye'.
jrockway 9y ago
You can represent all colors on three axes. If you choose each primary color so that it stimulates exactly one of your three color receptors, it is possible. However, there are no wavelengths of light with that property, so in real life, it's not possible to produce a monitor that can show you all colors you can see (with only three primaries, that is). You can see the various compromises that people have developed. sRGB has real primary colors (your monitor is probably using them right now), but there are many colors that it can't convince your eye to see. (There are also colors you can see that don't actually exist as a single wavelength of light; magenta for example.) Adobe RGB picks different primaries and you can see more colors. DCI-P3 picks still different primaries and gives you even more colors. But in the end, there aren't three points you can pick that will give you all colors. You can pick more than three primaries to get more colors. CMYK for printing is an example of this. If you want to mathematically represent all colors, that's easy. CIExyz does that, but the "primaries" can't even be called that because they have no relationship to human anatomy. This Wikipedia article is a good starting off point for understanding color perception: https://en.wikipedia.org/wiki/CIE_1931_color_space https://en.wikipedia.org/wiki/CIE_1931_color_space (As for computer use, I tried a wide gamut display once and it's a disaster. 99.99% of all content is sRGB, so you might as well have your monitor using sRGB primaries. The metadata situation is too broken for browsers or the OS to know what color space an image is actually in -- displaying an sRGB image with Adobe RGB primaries makes images unreasonably vibrant. Displaying an Adobe RGB image with sRGB primaries looks ridiculously washed-out. Adding to the fun is that browsers like Chrome will convert so that things look right... but assume display colorspace if there is no metadata in the image. And all the photo and art sharing websites I checked a couple months ago actually delete that metadata, so if you compose your images in a colorspace other than sRGB, most people will see the wrong colors. It sucks. I took up black-and-white photography. Everything can display that :) I would say I'm surprised that there are no monitors that use more than three primaries to display color... but the reality is that even wide-gamut 3 primary color is so broken that it's probably not even worth trying. You could see more colors, but nobody else would see the right colors. Why even bother, I guess.

tbabb 9y ago

All of those things about visual processing are true. > You can't reduce it to three axes. This is my claim: It is possible to represent all possible visual stimulus with: f(direction, time) -> (a, b, c). That is what I mean by "vision is three dimensional". It is not possible to add another channel "d" to the (a,b,c) tuple which is not redundant; so anything you add would not be an extra axis or increase the dimensionality of the perception space. The brain/retina may generate lots of extra "channels" from processing this (moving) three-valued image, but those extra channels can't be stimulated independently of each other; they depend entirely on those original three degrees of freedom as a function of space and time. In that sense they aren't really "axes", because they aren't degrees of freedom. That's what I mean by "there isn't an extra channel." If you agree with that, then we don't disagree and we are just arguing semantics. :)

edejong 9y ago
It’s funny that you introduce time in your equation, because it shows how your view is incomplete. In our visual system, you cannot reduce to three dimensions without creating a recursive relation. It should be more like: Ret(a,b,c)_t = f(Ret(a,b,c)_{t-1}, current_stimulus) Since it is a recurrence, we cannot reduce to three dimensions.
shawnz 9y ago
Couldn't you use this same line of thinking to argue that only one dimension is required? Our eyes may generate 3 channels, but don't they depend entirely on the frequency of light received which is one dimensional?
- krallja 9y ago
  Light is not perceived at a single frequency. It is a spectrum. That’s why you can see non-spectral colors like pink.
  - shawnz 9y ago
    OK, well, are there any colours which are not representable with two frequencies? That is still less than three dimensions.
    - krallja 9y ago
      White.
      - shawnz 9y ago
        Isn't that representable with a mixture of blue and yellow light?
        tbabb 9y ago
        You can pick a blue and a yellow and a proportion at which to mix them which will produce white, but for any two primaries you pick, there are a multitude of colors you can't represent. For example, if your basis is blue-yellow as you suggest, then you can't represent red or green (and an infinity of other colors off-axis). Fundamentally the chromaticity diagram[1] is 2D (with a third axis for intensity). You need to mix at least three points to span the space of the plane. [1] https://dotcolordotcom.files.wordpress.com/2012/08/anatomy-of-a-cie-diagram2x.png https://dotcolordotcom.files.wordpress.com/2012/08/anatomy-o...
Balgair 9y ago
To be fair, the receptors are VERY time dependent too. Take a stare at the top bar for ~20 seconds and then move your eyes down just a bit. You'll see an echo image of the opposite color (colorblindness depending). This shows that even a 'little' time spent saturating the retina will effect the later images. As other people mention, the retina does a LOT of pre-processing before any 'signal' gets sent. The very first synapse from the receptor is heavily modified by horizontal and bipolar cells in a time-dependent reactive manner. The 'images' we 'see' are nothing like what the retina 'sees'. People with cataracts will commonly have very advanced occlusions before thinking there may be a problem, due to the incredible amount of processing the retina itself does. They really cannot 'see' that they cannot 'see'. So, trying to reduce vision to a color mapping is just so ... computational. Biology is not like that all the time. It's not a 'map' like with sound and hearing (where tonotopy is semi-conserved throughout brain processing). With vision, things are used as 'information' almost instantly, but for certain by the end of the LGN into V1. You can't really backtrack the data through the system once it hit V1, it self-modifies the memristance of the synapses too quickly to chase the action potentials again. So thinking of things as 'red' isn't what the brain wants to do, it's not matrix algebra. It's 'grandmother' and 'tiger' and 'that-look-in-her-eye'.

jrockway 9y ago

You can represent all colors on three axes. If you choose each primary color so that it stimulates exactly one of your three color receptors, it is possible. However, there are no wavelengths of light with that property, so in real life, it's not possible to produce a monitor that can show you all colors you can see (with only three primaries, that is). You can see the various compromises that people have developed. sRGB has real primary colors (your monitor is probably using them right now), but there are many colors that it can't convince your eye to see. (There are also colors you can see that don't actually exist as a single wavelength of light; magenta for example.) Adobe RGB picks different primaries and you can see more colors. DCI-P3 picks still different primaries and gives you even more colors. But in the end, there aren't three points you can pick that will give you all colors. You can pick more than three primaries to get more colors. CMYK for printing is an example of this. If you want to mathematically represent all colors, that's easy. CIExyz does that, but the "primaries" can't even be called that because they have no relationship to human anatomy. This Wikipedia article is a good starting off point for understanding color perception: https://en.wikipedia.org/wiki/CIE_1931_color_space https://en.wikipedia.org/wiki/CIE_1931_color_space (As for computer use, I tried a wide gamut display once and it's a disaster. 99.99% of all content is sRGB, so you might as well have your monitor using sRGB primaries. The metadata situation is too broken for browsers or the OS to know what color space an image is actually in -- displaying an sRGB image with Adobe RGB primaries makes images unreasonably vibrant. Displaying an Adobe RGB image with sRGB primaries looks ridiculously washed-out. Adding to the fun is that browsers like Chrome will convert so that things look right... but assume display colorspace if there is no metadata in the image. And all the photo and art sharing websites I checked a couple months ago actually delete that metadata, so if you compose your images in a colorspace other than sRGB, most people will see the wrong colors. It sucks. I took up black-and-white photography. Everything can display that :) I would say I'm surprised that there are no monitors that use more than three primaries to display color... but the reality is that even wide-gamut 3 primary color is so broken that it's probably not even worth trying. You could see more colors, but nobody else would see the right colors. Why even bother, I guess.