Color theory question ....

Discussion in 'Photoshop Tutorials' started by Wdflannery, Jan 9, 2004.

  1. Wdflannery

    Wdflannery Guest

    This is something that puzzles me ..... I understand sound theory pretty
    well... and we know sound is vibrating air ....for pure tones the air pressures
    varies as a sine wave.... and, color is a vibrating electromagnetic field
    ......again with pure colors represented by sine waves .....

    Here is what I don't understand ...how is it that you can, as I understand,
    choose 3 primary colors..... and mix them to get any color at all ????? It
    seems quite unlikely .... for example.... when three sinewaves of different
    frequencies are added, the result is not a pure sinewave at a different
    frequency .... suggesting to me that you can't generate the pure colors, much
    less all the colors.

    And, no one would suggest that you can take 3 pure (sound) tones and generate
    all the pure tones, much less all the sounds ..... so, what is it about light
    that is different from sound .. ?????

    Is there any easy explanation ???? Or a link I could check, to relieve my
    bafflement????
     
    Wdflannery, Jan 9, 2004
    #1
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  2. In very simple terms, the frequency of the light reaching the retina is
    perceived as a specific color. It isn't that colors are somehow being
    mixed in the waves, it's that the eye is perceiving a very narrow range
    of EM energy as a color. Shift the frequency slightly, and the perceived
    color changes. The human eye is capable of distinguishing tens of
    thousands of different frequencies (colors).

    The "primary colors" are something of an abstraction used by various
    human endeavors to make synthesis of the full spectrum of colors simple.
    Instead of having to have a phosphor that reacts precisely to every
    wavelength (color) of light, you measure the RGB values of the light at
    that point, and use the values to synthesize an equivalent color value.
    At output, instead of having a phosphor that can produce any color in the
    spectrum, you use the simpler technique of combining the RGB components
    to produce what the eye perceives as a dot of a particular color.

    The notion of light being sine waves like sound is not quite accurate.
    Remember that photons show the characteristics of both waves and
    particles - and I'm not sure it's been established exactly how the retina
    responds to these varying frequencies and perceives them with such fine
    differentiation.
     
    James Gifford, Jan 9, 2004
    #2
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  3. Wdflannery

    J C Guest

    There is no one-to-one correspondence between sound and light. They
    are not the same thing. Do not even consider them together. Sound at
    its basic unit is simply particles of matter coliding against each
    other. When we hear a violin, we are perceiving a rhythmic pattern of
    the air hitting our ear drum. Sound cannot move through a vacuum.
    Light can. Light is an actual physical entity (albeit one that is
    still not fully understood by even top physicists -- read what string
    theorists have to say about light if you really want to get freaked
    out).


    -- JC
     
    J C, Jan 9, 2004
    #3
  4. Wdflannery

    Warren Sarle Guest

    It's a matter of the neurophysiology of color perception. The retina
    contains
    three kinds of color receptors, which you can think of as outputting
    something very roughly like an RGB color space. As the nerve impulses
    travel towards the brain, they get transformed into something very roughly
    like LAB space. Further on, many more complicated transformations are
    performed that some people spend their whole lives trying to understand,
    with limited success. But the fact that 3-dimensional color spaces like
    RGB and LAB work is based on the the three kinds of color receptors.
    There are other species with either more or fewer than three kinds of
    color receptors; if they had invented printing and computers, they would
    have used color spaces with more or fewer dimensions.

    Sound receptors in the ear are totally different, since there are receptors
    for many different wavelengths of sounds. Therefore, the perception of
    sound cannot be reduced to a low-dimensional space.
     
    Warren Sarle, Jan 9, 2004
    #4
  5. Here is the way I see it.
    A plucked string, for instance, causes a single frequency (say 1000 Hz) plus a few
    overtones (2000, 3000.....N)at much reduced intensity. There are no intermediate
    frequencies say, 1018 Hz or 1759 Hz. So basically we do no have a CONTINUOUS
    spectrum of frequencies. Even if we pluck 3, 4, 5 strings we will get discrete
    frequencies and their overtones, PLUS their sum and difference frequencies. But
    still not a continuous spectrum of frequencies.
    Perhaps if you plucked a thousand different strings simultaneously, you would get
    enough fundamentals, overtones and sum / difference frequencies interacting that we
    would get something akin to "WHITE NOISE"
    With Light, however, when we refer to e.g., "RED" light, we mean we get a
    CONTINUOUS spectrum of frequencies with a gaussian distribution from about
    600-750 nm. "GREEN" may mean a similar continuous frequency distribution around
    500-650 nm. Similarly "BLUE " means a continuous distribution around 400-550 nm.
    So any color, say orange (610 nm) is present in what we call RED. It is also
    present in what we call GREEN.
    By mixing equal amounts of RGB we get a continuous spectrum that contains every
    conceivable frequency in the Visible range. We call this "WHITE LIGHT". By mixing
    various amounts of RGB we get different hues of color.
    If we used equal amounts of pure MONOCHROMATIC laser light at say 680.00 nm
    (Red), 525.00 nm (Green), and 470.00 nm (Blue), we would not get white, because the
    combination does not contain ALL frequencies in the visible spectrum. I won't even
    go into how the retina and the brain convert this information into the perception
    of color.
    Bob Williams
     
    Robert E. Williams, Jan 9, 2004
    #5
  6. Wdflannery

    Warren Sarle Guest

    This may or may not be the case. What we perceive as red light may have
    a very narrow or a moderately broad range of frequencies.
    If the intensities are balanced properly, it will in fact be perceived as
    white.
     
    Warren Sarle, Jan 9, 2004
    #6
  7. Wdflannery

    Xalinai Guest

    Other than acoustic waves that (mechanically) interfere with each
    other in the transport medium lightwaves do not interact.

    The human eye responds to certain frequencies of light and most of the
    color impression is created in your brain as a result of amount and
    intensity of only three major areas of frequence in the range of red,
    green and blue.

    That the frequencies are still available separately can be checked
    using different laser colors (with a very narrow bandwidth) on one end
    and a prisma on the other end - there is no modulation of frequencies
    and demodulation.

    Michael
     
    Xalinai, Jan 9, 2004
    #7
  8. It's quite simple, you may learn about it at:
    http://www.bradford.ac.uk/acad/lifesci/optometry/resources/modules/stage1/pvp1/Colour.html

    HTH ;)
    Peter
     
    Peter Wollenberg, Jan 9, 2004
    #8
  9. Wdflannery

    Mike Russell Guest

    Yes, there are many useful analogies between sound and light. Both are wave
    energy phenomena, and both have the concept of mixed frequencies.
    Your intuition is accurate. It's not possible to generate all the colors
    from three primaries, but you can generate a good approximation, and let the
    eye, which is very good at this, put the pieces together into something
    reasonable.
    The difference is between the eye and ear, more than between sound and
    light. Where the eye merges three frequencies of light into a single color,
    the ear will hear a chord when three frequencies are present

    You can fool the eye into thinking a particular frequency is present by
    using the correct ratio of red, green, and blue, as well as create new
    colors between red and blue that don't exist in the spectrum. The ear is
    smarter in this regard in that it takes all the frequencies apart instead of
    lumping them together, so you hear chords.

    This is because the eye uses just three overlapping detectors that are
    sensitive to red, green, and blue. The ear uses an array of thousands of
    hair cells, each tuned to a slightly different frequency, to extract more
    information from the perceptual mix than the three detectors in the eye are
    able to.

    The ear works like a spectrophotometer and the eye is more like a
    colorimeter.

    Of course, the ear has an easier job, since it doesn't have to create and
    interpret an acoustical image based on the sound reflecting from the objects
    around you. Experiments with acoustic holograms have been done, and in the
    natural world, bats and owls, do some of this.

    You could conceivably build a smarter eye in the form of a digital camera
    that gathers complete frequency information at each and every pixel - maybe
    this will happen some day. For now the technology isn't there, and our
    cameras use mixed arrays of sensors that are filtered for a relatively small
    number of colors, very similar to the way the eye works.
    Everything you need is right here in c.g.a.p :)

    Take care.
     
    Mike Russell, Jan 9, 2004
    #9
  10. Wdflannery

    jjs Guest

    Rather than trying to explain it, may I suggest a rather enlightening and
    fun read? "Vision and Art: The Biology of Seeing" by Margaret Livingstone.
    Note the "biology" aspect. We perceive color in terms that the physics
    doesn't address in the pure abstract.
     
    jjs, Jan 9, 2004
    #10
  11. Wdflannery

    jjs Guest

    Recent literature which covers the physiology of the eye does a very good
    job of describing how the normal human eye perceives color. How the eye
    works is astonishing, and to learn how it cannot see certain colors is
    equally surprising.
     
    jjs, Jan 9, 2004
    #11
  12. Wdflannery

    jjs Guest

    Keep in mind that the normal human eye sees _certain_ colors which exist at
    near-opposite ends of the true spectrum as the same color.
     
    jjs, Jan 9, 2004
    #12
  13. Wdflannery

    jjs Guest

    Which is irrelevant to how the eye works. The eye infers color using rather
    fuzzy logic which depends upon a kind of interference.
    Most of the color is made from signals in the eye. The brain cannot image
    what the eye does not first render.
    The human eye does not see all the colors in the so-called visible spectrum.
    There are areas of less and greater sensitivity. You might say the eye is
    hue-disadvantaged.
     
    jjs, Jan 9, 2004
    #13
  14. Wdflannery

    Bobs Guest

    And some animals have color perception that exceeds our own. Birds of
    prey, for example, have 4-color receptors instead of 3, thus adding a
    whole dimension of color discrimination (compared to human vision).
     
    Bobs, Jan 9, 2004
    #14
  15. Wdflannery

    Wdflannery Guest

    Amazing. Thanks to all. Great info.
     
    Wdflannery, Jan 9, 2004
    #15
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