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B Why there is no frequency for the color brown?

  1. Jun 13, 2017 #1
    Hi All,

    Is it true that the brown color has not a single frequency attached to it?

    Best regards,
    DaTario
     
  2. jcsd
  3. Jun 13, 2017 #2

    Dale

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    The same is true of white, or gray, or purple.
     
  4. Jun 13, 2017 #3

    Drakkith

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    The only colors which have a corresponding frequency(or rather a small, continuous range of frequencies) are spectral colors.
     
  5. Jun 14, 2017 #4

    sophiecentaur

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    Doesn't it just make you cross that even 'reputable' Science sources confuse wavelength and colour? :mad:
     
  6. Jun 14, 2017 #5

    Drakkith

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    Indeed. It makes me 655 nm in the face. :-p
     
  7. Jun 14, 2017 #6
    Is it correct to say that there are colors which are not expressible in terms of a thin an monomodal spectrum?
     
  8. Jun 14, 2017 #7

    Dale

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    Yes, see my previous reply for a few examples of such non spectral colors.
     
  9. Jun 14, 2017 #8
    I saw it. Thank you for sharing, Dale. So it seems that the concept of color has something of the physiology of eye inside, isn´t it?
    I have heard of metamerism, i.e., visible radiations with different spectra but recognized by the eye as having equal color. Does it imply that the color concept does not have even an objective association with spectrum?
     
  10. Jun 14, 2017 #9
    The measurement of color makes use of the reflectance of the object (spectrum), the light source and the three color response curves (color matching functions) for human vision.
     
  11. Jun 14, 2017 #10

    Drakkith

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    The perception of color is extremely complicated and involves both the eye and the brain. It is also very much subjective. For example, my stepfather is red-green colorblind. To him, a green streetlight at an intersection looks almost exactly like the white streetlights that light up parking lots and such. The green streetlight is just a bit dimmer than the white lights. So for him the spectral color green looks very much like a non-spectral color. He also has difficulty seeing the color yellow. The standard wavelengths given for each spectral color don't apply to him at all.

    In addition, even for color-normal people, the brain actively works to make sure that your perception of color changes as little as possible between various environmental light sources. Your perception of the color of your shirt is probably very similar no matter if you're sitting under white fluorescent lights in an office or under a yellowish incandescent at home.
     
  12. Jun 14, 2017 #11
    There are tetrachromatic women who see more colors than most of us. So if you are not so lucky, you see many things as the same color, which they see as different colors.
     
  13. Jun 15, 2017 #12

    sophiecentaur

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    It's always worth while referring to the CIE chromaticity chart when discussing colorimetry. It's really worth reading around all the sites that a Google search will throw up. Visible colours (the only colours that exist because colours are in your head) The chart is a totally artificial representation of our (average) perception of colours and mixes of colours and I'm sure there are purists who will cast doubt on such a simplistic representation but the whole mechanism is pretty fuzzy and the accepted human colour analysis curves are only based on 'average' performance.
    I'm not sure what you are suggesting here, exactly but it is not actually possible to produce a metemeric match of a spectral colour (i.e. a narrow band of frequencies) by using any combination of primaries because the locus of the spectral colours on the CIE chart is a curve and any straight line joining two primaries will not pass through the required spectral colour. (on the actual curve) You can produce a 'good' yellow (association?) with equal values of R and G signals applied to TV tube primaries but it does not lie on the CIE curve. It will be a 'desaturated' version of spectral yellow and an observer will be able to tell the difference.
    There is a difference between how you do colorimetric research and how you make a TV system. The 'best' primaries to use would be monochromatic and spectral but you would never get enough brightness from a narrow band synthesised primary so the ones used are on the vertices of triangles and the spectra of those primaries are far from monochromatic. The gamut of obtainable metameric matches is limited to those colours within the triangle. Note the number of bright clothing colours at sporting events that appear to be the same on the screen. That (imo) must be because they are very saturated and lie outside the obtainable gamut and turn up on the sides of that triangle. If you were at the venue, you would distinguish between all those different bright red kagouls.
     
  14. Jun 15, 2017 #13
    You are not studying the correct category. You have to look into the wavelength.

    It's a simple matter of looking it up.
     
  15. Jun 15, 2017 #14

    sophiecentaur

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    To whom is your remark made?
     
  16. Jun 16, 2017 #15
    Color perception is very complex indeed. Just look at that picture that was going around with the yellow (or blue?) dress. The wavelengths and strengths were exactly the same, but to some it looked yellow, to some it looked blue (mostly dependent on where they were looking at the picture).
     
  17. Jun 16, 2017 #16

    sophiecentaur

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    The Land Retinex theory of colour vision attempts to quantify how we actually perceive colour. See this link and then Google the terms: Land, Retinex Mondrian. It is fascinating and it amazes me that, in the light of his work, colour TV works so well!
     
  18. Jun 16, 2017 #17
    I think that was just a matter of whether someone's browser was properly color managed and their monitor calibrated (so as you say, where they were looking at it). It didn't really have to do with color perception per se.
     
  19. Jun 16, 2017 #18

    Drakkith

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    Sure it did. People would get into arguments over the color after looking at the picture on the same monitor.
     
  20. Jun 16, 2017 #19
    That's news to me. There are variations of vision from person to person, but would people looking at the same monitor disagree about whether the dress were yellow or blue, in such large numbers as to become an internet sensation?
     
  21. Jun 16, 2017 #20
    Yes, they did. I have seen this at work. The same picture on the same phone. Every body, including visitors, was asked about what he/she sees. Definitely two groups, the white-gold group maybe slightly more numerous.
     
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