Simulating an orange filter in Photoshop

Discussion in 'UK Photography' started by Al Treacher, Aug 22, 2003.

  1. Al Treacher

    Bart Guest

    Good work tony! Now you've bothered looking up this term in a dictionary you're
    only one step from grasping how a real life orange filter works :)
    The only decent arguments in thread are coming from these 'idiots'.

    What you probably want to tell us is that for almost everyone the effect of
    applying an orange filter effect in photoshop looks like the photo was shot
    with an orange filter. But if you compare this photo with an bw-picture of the
    same scene actualy shot with an orange filter, there will be differences. For
    some subjects or scenes this difference will be hardly noticable, but form some
    (dependent on the spectral-reflectance properties of the subjects) the
    different will be very noticable.

    Bart
     
    Bart, Sep 2, 2003
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  2. Actually, it doesn't have to match the sensitivity of the 3 receptors in
    the eye. It turns out that the eye's receptors are quite wierd,
    probably for evolutionary reasons, with two long-wavelength responses
    that are only moderately different, and one short-wavelength response
    that is very different. The eye and brain process these to get what we
    see.

    What *is* important is for the camera to use any set of filters whose
    responses are a linear combination of the human colour matching
    functions. That means that the camera outputs can be processed to give
    the same colour rendition as the human eye. But the camera designer
    will pick physically realizable filters that maximize sensitivity and
    minimize noise introduced in processing, not actually try to match the
    responses of the cone cells in the eye.
    I don't agree. The response of pan film is part of the reason why B&W
    images look "different". But an orange filter changes the colour
    rendition for both B&W and colour images - it makes colours that
    formerly looked the same now look different. In B&W it is perhaps more
    obvious, because there's no orange cast and you can't immediately tell
    what filter was used, you just sense that the image is different. In
    colour, if the image looks orange, you can tell what was done. But if
    you use an orange filter on the camera, then colour balance the
    resulting image to get rid of the orange cast, the resulting colour
    image will still be a bit weird.

    RGB adjustments can't fully duplicate the effect of an orange filter,
    whether the ultimate output is a B&W image, an orange-tinted colour
    image, or a colour-neutral colour image. RGB adjustments *can* easily
    produce a colour image with an overall orange cast; it just isn't the
    same as what you get shooting through an orange filter.

    Dave
     
    Dave Martindale, Sep 3, 2003
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  3. Al Treacher

    Fred Allsop Guest

    And simulating a red mist?
     
    Fred Allsop, Sep 3, 2003
  4. What is harder to simulate is a fog (colored or not) where the
    fogginess is a function of the distance, i.e. far away things
    tend to dissappear in the fog. To simulate that you need a depth
    map, a.k.a. Z-buffer in 3D rendering.


    Roland
     
    Roland Karlsson, Sep 3, 2003
  5. Thanks, Dave, that's something else I didn't know. Can you give me a
    pointer to a simple but more detailed explanation? Most of my eye-brain
    knowledge comes from Richard Gregory at Bristol uni.; I note you are
    from a different part of the world.
    Yes, I understand that - i.e. the practical must compromise the
    theoretical!
    ISTM that you are agreeing! In my B&W days (1955-85 mainly) I often
    looked thru an orange filter and made mental adjustments as to how the
    final result would appear. The darkening of the (blue) sky was always
    more dramatic on the film than my eye saw it. But I also agree that to
    some extent it differentiated between different foliage colours
    (especially in Spring).
    Not to mention that the saturation of the yellow-red sensors limits the
    "tonal range" available to them.
    Which is, I think, the point I was making. (and which you have said all
    the way along, I know.)

    Thanks for the informed comment, Dave.

    Mike
    [The reply-to address is valid for 30 days from this posting]
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    Michael J Davis
    <><
    Some newsgroup contributors appear to have confused
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    Michael J Davis, Sep 4, 2003
  6. Al Treacher

    Mark Roberts Guest

    In Galen Rowell's book "The Inner Game of Outdoor Photography" he has a
    chapter devoted to reference books, including many on human visual
    perception. I could probably post some of his list or put it on my web
    site.
     
    Mark Roberts, Sep 4, 2003
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