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Color Tutorial

  1. Dec 19, 2009 #1
    Does this make sense?





    This is the sensitivity of the 3 human cone cells.

    http://img192.imageshack.us/img192/4562/28030351.jpg [Broken]

    This is the range of different colors that the human eye can see.

    http://img696.imageshack.us/img696/9397/31986914.jpg [Broken]

    This color would appear white.

    http://img687.imageshack.us/img687/7622/38524108.jpg [Broken]

    This color would appear gray.

    http://img687.imageshack.us/img687/2720/40928929.jpg [Broken]

    And this color would appear dark gray/almost black.

    http://img339.imageshack.us/img339/4922/71486004.jpg [Broken]

    This color would appear green.

    http://img705.imageshack.us/img705/2658/49001107.jpg [Broken]

    And this would be a less saturated green.

    http://img97.imageshack.us/img97/379/46565217.jpg [Broken]
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Dec 20, 2009 #2

    Cleonis

    User Avatar
    Gold Member

    Yep, that looks similar to me to other representations of human cone cell sensitivity.
    Maybe you ought to remark that in this representation the sensitivity lines are recalibrated to have their peaks at the same height. In other diagrams that I've seen the leftmost line, the blue one, was much less high than the other ones.
    Of course, in effect the retinal nerve cells perform just such a "recalibration", so that the proportions of the different colors in daylight come out to be perceived as colorless.

    I concur.


    Yes, providing you mention that the perception of gray is primarily dependent on the ratio of contributing colors in the light that falls on the retina, not on total light yield.

    For instance, suppose I'm in a hardly illuminated room, looking at a computer screen, displaying white (with the screen brightness set at 100%) That sure looks white.
    Then I adjust the screen brightness to 50%. Then after my eyes have readjusted to the new situation the screen will still look white.
    The perception of what the screen shows is constructed by comparison with the surroundings. The surrounding is a hardly illuminated room, so the computerscreen set to brightness 50% still outshines anything in the room. Under those circumstances the light from the computer screen will be perceived as white.

    Conversely, if you flood a room with white light (either daylight or from lamps), then if you outshine the computerscreen you will percieve the displayed "white" as grayish. (However, your knowledge/memory that the screen is displaying white will probably bias your perception.)

    I concur


    As in the case of perceiving shades of gray, there is also the element of comparison with the surroundings.

    Cleonis
     
    Last edited by a moderator: May 4, 2017
  4. Dec 21, 2009 #3
    I get confused when thinking about chromaticity spaces and desaturation. The CIE diagram is a chromaticity space that shows no change in brightness. Does this means that all of the hues are shown at full brightness? Every monochromatic color plus the extra spectral purples are desaturated by being mixed with the white in the center of the diagram right?

    http://www.gis.zcu.cz/studium/pok/Materialy/Book/resources/CIE1931.jpg [Broken]

    How can a color be mixed with white to desaturate it when white looks like this:

    http://img687.imageshack.us/img687/7622/38524108.jpg [Broken]

    and green looks like this?:

    http://img705.imageshack.us/img705/2658/49001107.jpg [Broken]

    The spectral curve of white engulfs the spectral curve of green which should make it impossible to mix the two right?

    If the spectral curve of the desaturated green looks like this:

    http://img97.imageshack.us/img97/379/46565217.jpg [Broken]

    And the spectral curve of gray looks like this:

    http://img687.imageshack.us/img687/2720/40928929.jpg [Broken]

    Then wouldn't the green have been mixed with gray instead of white to desaturate it?

    I hope this makes sense and if it doesn't please tell me why.

    Thanks
     
    Last edited by a moderator: May 4, 2017
  5. Dec 23, 2009 #4
    I am getting no replies so I guess I'm making no sense. I simply want to figure out how our eyes see all the different colors that they can see and how brightness and saturation relate to all of them. I understand that white light is sent to us from the sun and contains all of the hues that we can see due to our 3 cones with overlapping sensitivities. But I don't understand how brightness and saturation work together to make the possibility of different distinguishable colors a lot greater. It is driving me crazy that i cannot figure this out. There is something big that i am not understanding because i have been trying to figure this out for months now with no luck. Please, Please help me out.
     
  6. Dec 23, 2009 #5

    Cleonis

    User Avatar
    Gold Member

    I have to say, the prospects for you figuring it out are not good. If it would be within your capacity you would by now have located sources of information that answer your questions.


    For now all I can do is repeat. I copy and paste from my earlier reply.

    Perception of gray is primarily dependent on the ratio of contributing colors in the light that falls on the retina, not on total light yield.

    For instance, suppose I'm in a hardly illuminated room, looking at a computer screen, displaying white (with the screen brightness set at 100%) That sure looks white.
    Then I adjust the screen brightness to 50%. Then after my eyes have readjusted to the new situation the screen will still look white.
    The perception of what the screen shows is constructed by comparison with the surroundings. The surrounding is a hardly illuminated room, so the computerscreen set to brightness 50% still outshines anything in the room. Under those circumstances the light from the computer screen will be perceived as white.

    Conversely, if you flood a room with white light (either daylight or from lamps), then if you outshine the computerscreen you will percieve the displayed "white" as grayish. (However, your knowledge/memory that the screen is displaying white will probably bias your perception.)


    Cleonis
     
  7. Dec 23, 2009 #6
    Is this true with all other colors too? not just white?
     
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