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Thread: Question: "How do the eye lenses see the colors?"

  1. #1 Question: "How do the eye lenses see the colors?" 
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    Hi all, I'm an undergraduate student focused in Computer Science. Now I have a research in Computer Graphics about Color Vision Deficiency. I can't explain too much about it, just now.

    This is my first time using this forum. I don't know so much about Physics, especially about lenses or optics. That is may problem. I want to know how do the eyes process an image captured by its lenses. Is there any formulas which explain how to combine the image (colors) by two lense (right and left eyes)? What if the left eyes see green and right eyes see red combined in our brain and product the vision? And what kind of optical theory can explain the detail about this case?

    --

    Gin


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  3. #2  
    Forum Bachelors Degree Waveman28's Avatar
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    The eyes focus incoming light through the lenses onto the retina in the back of the eye, which contains cones and rods. Cones are responsible for the detection of colour, while rods help with motion detection, determining white light saturation etc. These cones and rods send electrical signals to the brain where they are turned into an image. Is this the kind of answer you were after? Your question(s) was a little confusing at first.


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    Sorry if my question is confusing, :-D. I've read rods and cones before. In a normal vision people capture a same object and same colour with their eyes. But we can set a diferent object or colour between two eyes. An example, I use a green lense in my left eye and a red lense in my right eye. We know that the colored lense can filter light and change an object from nature colour. If I do it, how the electrical signals turn an object into an image? It will be diferent with a normal case, won't it?

    I still find such a journal science telling this. Thanks for answering my question.
    Gin
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  5. #4  
    Forum Bachelors Degree Waveman28's Avatar
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    Putting different colour filters in front of each eye such as red and green filters certainly will have an effect on the final image generated in the visual cortex of the brain. This effect is exploited to make cheap glasses that can be used to give the illusion that a certain 2D object such as a picture is 3 dimensional. The exact reason for this I cannot remember off the top of my head, but I think it has something to do with the fact that the left and right eye in humans are actually slightly different in anatomy and also the way that the brain combines the two individual images together to form a single image.
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    Veracity Vigilante inow's Avatar
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    Gin - Sites like the one linked below might help you to better understand the basics. It's important to know that the lenses really have nothing to do with the perception of color. Lenses are there merely to focus the light. Once that light is focused, it then hits the different receptors at the retina. Some cone receptors "fire" only when they are hit with red light, while other cone receptors "fire" only when they are hit with blue light, whereas other cone receptors "fire" only when hit with green light. It's the aggregate firing pattern of all of those different cone receptors (which ones fired, which ones didn't) that allows our brain to interpret the signal and identify overall color. It's a lot like an algorithm... this much X plus that much Y combined with this much Z results in hot pink, for example.

    Again, sites like the below may be useful to you. Good luck with your project.

    http://faculty.washington.edu/chudler/eyecol.html
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    Waveman28 - You remind me that a 3D glasses is formed by a different color lenses. Finnaly, I'll learn the basic how to form both single images.

    inow - That is an interested sites. It help me to understand the color vision. It's like RGB color model in computer graphics.

    Thanks all.
    Gin
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  8. #7  
    Forum Radioactive Isotope MagiMaster's Avatar
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    Hello fellow computer scientist.

    It's a good question. I'd look into anaglyphs. I know that you can see some colors in the better made ones, so the brain will interpret left/right color pairs as a single color, at least some of the time. (I know when I'm looking at stuff like that, I see all three versions off and on.)
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  9. #8  
    Forum Masters Degree Twit of wit's Avatar
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    On color deficiency - yes the colors of the pigments and how they are combined to distinguish colors is known. You will probably need medical literature, not physics. Also note that "colour deficiency" usually means that some colors are shifted compared to the standard, not an actual defficiency of any kind. (that's why most colorblind people don't know they are colorblind until they are tested)

    The images from two eyes are not combined for color perception, they are combined for the perception of depth.
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    Hello gin2_fm

    You really need to get hold of "The Eye - a Natural History" by Simon Ings, a brilliant book on colour and the brain.

    Colour vision lies in the retina, not the lens, although dispersion in the lens can make blue-on-red printing difficult to focus on.

    The colour vision cells in the retina are in two forms, long wavelength and short wavelength. The long wavelength cells are smaller and contain one of two different rhodopsins, so they can sense either red or green. The short wavelength cells contain a third rhodopsin, detect blue and are much larger and go deeper into the retina, are much fewer in number (not many at all in the foveal pit) and do not contribute to a sense of brightness. So yellow, which is red and green - all long wavelength cells firing - is a bright colour, while pure blue (not sky blue which mixes in some red and green) is intrinsically a dark colour. Gluing the colour into the image happens surprisingly late on in the visual cortex. Shape processing happens much sooner - you can recognise faces in black and white.

    There is some evidence that different people have different rhodopsins for red or green in particular. This does not give you colour blindness unless the red-green sensitive wavelengths get too close to each other, but affects how warm you perceive orange to be (say). And where one person might perceive a brownish red another might see a kahki. This led to certain soldiers being valued in WWI for being able to discriminate the primitive camouflage dyes used then.

    Good luck with your work.
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    Forum Masters Degree Twit of wit's Avatar
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    Quote Originally Posted by muppet
    There is some evidence that different people have different rhodopsins for red or green in particular. This does not give you colour blindness unless the red-green sensitive wavelengths get too close to each other, but affects how warm you perceive orange to be (say). And where one person might perceive a brownish red another might see a kahki. This led to certain soldiers being valued in WWI for being able to discriminate the primitive camouflage dyes used then.

    Good luck with your work.
    You don't have to be unable to distinguish colors to be diagnosed as colorblind, any difference in colour perception is sufficient.
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  12. #11  
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    Quote Originally Posted by Twit of wit

    You don't have to be unable to distinguish colors to be diagnosed as colorblind, any difference in colour perception is sufficient.
    In general if you pass the standard colour blindness tests you are not considered colourblind. All the tests do is determine your ability to discriminate between certain colour bands. Minor differences in colour perception can occur (like a small shift in the "red" cell colour pigment) from a variant gene without materially affecting your discrimination, and for some shifts can improve discrimination in certain parts of the spectrum. Some trials have indicated that as many as 40% of men have variant genes here without being colourblind, but these tests are notoriously tricky to do so one has to treat these numbers with caution.

    There is also the possibility of the rare woman (tetrachromat) who can inherit three pigments in the red-green range, and when added to the blue gives four-colour vision. This difference in colour perception materially improves discrimination in the red-green range. It is caused by them having different red / green DNA coding on each X-chromosome, and neither set is deactivated during foetal development. See http://en.wikipedia.org/wiki/Tetrachromacy
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  13. #12  
    Forum Masters Degree Twit of wit's Avatar
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    The tests are diagnosed to detects such changes, any change that will pass will mean only very minor change in perception. Exactly because the perception is just shifted is why are these tests done, people with those kinds of color blindness that cause inability to distinguish red-green colors are usually aware of it.
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    The tests are fairly crude and do not specifically test for shifts in perception, merely for the loss of discrimination. As I mentioned, research indicates that shifted perception is extremely common in the population, so colour blindness is simply the low percentage extreme state of this condition.

    If you really want to test for shifts in perception you need to add another set of cards to the standard set. This extra set is based on the fact that when you map a continuous spectrum into just three colour sensors, there will be different spectral combinations that produce the same colour sensation (or tristimulus value) in the eye. The crucial thing about this is that for two different spectral combinations to produce the same sensation, there must be a very specific set of colour receptors. Hence you decide what a "standard" gene set is, and you produce patterns in colours that will all map to the identical tristimulus value for the "standard" gene set; the lighting has to be controlled to avoid distorting the colours. Then any deviant gene set will see a pattern, but no-one with the standard gene set. The reason for doing it this way round is that there are too many combinations of variant genes, and you would have to have a set for each possible combination, so it's easier to access blind spots in the standard gene set.

    For myself, I am not colour blind, but my tristimulus values are certainly different to my wife's, different to one of my parent's, different to all but one of my siblings. Many husbands and wives argue over the exact colours of things. I nearly lost a summer job with BR because although the standard cards they tested me with showed me as not colour blind, I was unable to correctly identify a simulated green signal (gelatin dye), which to me looked nothing like a real green signal (coloured glass); it looked exactly the same as the real one to the tester, implying that for him the tristimulus values were identical, but for me they were not, implying in turn a different set of colour sensitive cells.
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  15. #14  
    Forum Masters Degree Twit of wit's Avatar
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    muppet: that is exactly what the tests do. Some cards contain numbers that can't be seen by people with normal vision but can be easily recognized by those with shifted colors. Those tests with comparing colors are entirely based on that and they are more precise.


    Which colours you perceive differently?
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  16. #15  
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    Well, ToT, I am afraid we have to disagree on this one, so let's leave it at that.
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  17. #16  
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    Edit:Hey, why did you delete it?
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