How are digital cameras able to render violet?

Discussion in 'Digital Photography' started by Paul Ciszek, Feb 11, 2013.

  1. Paul Ciszek

    Robert Coe Guest

    On Tue, 12 Feb 2013 20:30:57 -0500, Mort <> wrote:
    : James Silverton wrote:
    : >>
    : > I remember deep blue gentians in the Swiss mountains being reproduced as
    : > pink using Kodachrome and I was interested to get the same effect
    : > photographing deep blue petunias with a digital camera. Both cases are
    : > due to high reflectivity of UV light by the flowers.
    :
    :
    : Hi,
    :
    : I had a similar situation with morning glory flowers on Cape Cod, that
    : were blue to the eye and came out pink on Kodachrome. When I shot them
    : using Fujichrome, they came out the proper shade of blue, which greatly
    : pleased the amateur horticulturist that I was visiting.
    :
    : I gave up long ago on aiming for "exact true color", and am satisfied in
    : most cases with an approximation of the color. In some situations
    : involving Medical or Scientific subjects, accurate color is required. Of
    : course, now with digital photography, it is almost a moot point.

    The problem is, of course, that what constitutes "exact true color" is very
    much in the eye of the beholder. The human eye, films, and digital sensors all
    have their characteristic response curves to radiation in the visible spectrum
    (whatever that term means in such a broad context). We know, for example, that
    bees see bright, garish designs in flower petals that appear plain to us,
    because the designs reflect only ultraviolet light. Note the evolutionary
    intent: the flowers want to be attractive to bees, but to avoid being noticed
    as possible salad ingredients by humans, rabbits, grasshoppers, et al. The
    bees, in turn, find it advantageous to be able to identify tasty nectar
    sources that others miss. And as some have noted in this thread, different
    people (and probably different rabbits and bees) will have slightly different
    response curves and perceive colors slightly differently.

    The bottom line is that all of the Duck's (or Tony's or Peter's or others')
    formidable photo-editing skills can't guarantee that you or I will see exactly
    what he may have carefully prepared for us. The best that any of us can do is
    to tweak the available color settings to what looks "right" to us and hope
    that others will see things similarly.

    Bob
    Robert Coe, Feb 16, 2013
    #21
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  2. Paul Ciszek

    Robert Coe Guest

    On Thu, 14 Feb 2013 09:25:24 +1100, "David Hare-Scott" <>
    wrote:
    : Alfred Molon wrote:
    : > In article <>, Chris Malcolm says...
    : >> In part it's an artefact of a three primary colour space,
    : >
    : > Would the situation improve with four primary colours? Or more?
    :
    : Some women are tetrachromats, they have a rare mutation which gives them
    : two copies of the 'red' receptor with different sensitivity peaks. IIRC
    : it gives them slightly better discrimination in that end of the spectrum.
    : The interesting thing is that the brain integrates this into a coherent
    : picture of the world with no apparent effort.

    Does the second red receptor allow them to see into the near infrared?

    Bob
    Robert Coe, Feb 18, 2013
    #22
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  3. Robert Coe wrote:
    > On Thu, 14 Feb 2013 09:25:24 +1100, "David Hare-Scott"
    > <> wrote:
    >> Alfred Molon wrote:
    >>> In article <>, Chris Malcolm says...
    >>>> In part it's an artefact of a three primary colour space,
    >>>
    >>> Would the situation improve with four primary colours? Or more?

    >>
    >> Some women are tetrachromats, they have a rare mutation which gives
    >> them two copies of the 'red' receptor with different sensitivity
    >> peaks. IIRC it gives them slightly better discrimination in that
    >> end of the spectrum. The interesting thing is that the brain
    >> integrates this into a coherent picture of the world with no
    >> apparent effort.

    >
    > Does the second red receptor allow them to see into the near infrared?
    >
    > Bob


    I don't think so, its peak isn't very far from the normal 'red' one.

    D
    David Hare-Scott, Feb 18, 2013
    #23
  4. Robert Coe <> wrote:

    > The bottom line is that all of the Duck's (or Tony's or Peter's or others')
    > formidable photo-editing skills can't guarantee that you or I will see exactly
    > what he may have carefully prepared for us. The best that any of us can do is
    > to tweak the available color settings to what looks "right" to us and hope
    > that others will see things similarly.


    We can do a bit better better than that.

    We could use a standard monitor which (calibrated, of course)
    everyone uses. Then we will see the identical thing, though
    you may see them different due to your different wiring ---
    to which you are, however, used all your life. :)

    -Wolfgang
    Wolfgang Weisselberg, Mar 1, 2013
    #24
  5. Paul Ciszek <> wrote:
    > In article <kfedje$vr7$>, jgh <> wrote:


    >>I've seen in-camera colour processing be confused by a violet; it dealt
    >>with it successfully in "normal" mode but captured it as pink in "vivid
    >>colour".


    >>This was a dyed wool colour, outside on a bright snowy winter's day.


    > I suspect that any fabric dye that appears "violet" is in fact "purple",
    > i.e., reflects both red and blue light, just like the violet flower.


    The truth is just a spectrometer away. :)

    -Wolfgang
    Wolfgang Weisselberg, Mar 1, 2013
    #25
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