Forbidden/Impossible colors

Discussion in 'Human Science' started by Dinosaur, Jan 27, 2010.

  1. Dinosaur Rational Skeptic Valued Senior Member

    The February issue of SciAm has an interesting article about our color perception.

    It describes visual processing based on opposing colors: Red versus green & blue versus yellow. This process has been accepted for over 100 years as an explanation for various characteristics of human color vision.

    One aspect of the process is the absence of hues like reddish-green & bluish-yellow. These are impossible (or forbidden) colors for the human visual system, although the article describes experiments resulting in some capability for seeing such hues.

    Note, of course, that various other combination hues are easily seen: Bluish-green, reddish-blue (lavendar, purple), & reddish-yellow (orange).
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  3. S.A.M. uniquely dreadful Valued Senior Member

    Is there an example of such colours which are difficult to perceive? How do we see them? Do they look grey or something else?
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  5. Search & Destroy Take one bite at a time Moderator

    I used to have a colorful top but when I spun it, it changed into solid brown.

    reddish-green - should be brown
    bluish-yellow - should be green

    I think they are talking about a color for example that looks green and a little blue and a little yellow at the same time.

    Not sure though...
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  7. Blindman Valued Senior Member

    Are you talking additive or subtrative.

    Additive as in mixing coloured lights
    reddish-green = brown to yellow
    bluish-yellow = grey to white

    Subtractive as in mixing coloured paints
    reddish-green = black to dark grey
    bluish-yellow = black to dark grey
  8. Dinosaur Rational Skeptic Valued Senior Member

    Further comments relating to the SciAm article.

    The visible spectrum is usually described as: Violet, blue, green, yellow, orange, & red. Most people recognize far more than these six hues. EG: Purple & lavender rather than merely violet; Various bluish green or greenish blue hues instead of either blue or green; variations on red such as pink, crimson, maroon, & other reddish hues.

    A person with normal color vision can perceive hues which are combinations of red & blue: purples, lavenders, et cetera. The perceptual system indicates that such hues are a combination of red & blue.

    Similarly, there are hues which are perceived as being combinations of blue & green as well as those perceived as combinations of red & yellow (orange).

    People do not perceive any hue to be a combination of red & green or blue & yellow. Try to imagine such hues.

    With respect to the above, the difference between additive & subtractive mixing is not significant. Mixing ink or paint is a subtractive process, resulting in hues darker than the hues mixed & tending toward black. Mixing light is an additive process, resulting in lighter hues than the hues mixed & tending toward white.

    The primaries for the two processes are different, but either is capable of resulting in essentially the same range of hues. Yellow is a primary for subtractive mixing, while it is a mixture of red & green for additive mixing.

    To suggest the intent of the SciAm article, consider additive mixing.
    • Mixing red & green results in yellow, which is not perceived as a combination of red & green.
    • Mixing red & blue result in lavender, which is perceived as a mixture of red & blue.
    • Mixing blue & green result in bluish green or greenish blue, which is perceived (by most people) as a mixture of blue & green.
    People also perceive orange hues which are recognized as combinations of red & yellow. I do not know how this is done with additive color mixing.
  9. Fraggle Rocker Staff Member

    While many animals have fewer types of color receptors than we do, e.g. dogs and cattle, many have more, as many as seven. Many animals see far up into the ultraviolet. Birds that appear indistinguishable to us and make us wonder how they can tell males from females are actually distinctly dimorphic in the ultraviolet range. Many fish can also see ultraviolet.

    Bees and flowers evolved together. Flowers change hues in the ultraviolet as their nectar becomes riper, and bees have eyes that can tell the difference.
  10. Search & Destroy Take one bite at a time Moderator

    hey blindman. I am just wondering how someone might get a black after mixing blue and yellow together. Ask a kindergarten class and they will definitely answer GREEN.

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