Depth perception and contrasting colours

Discussion in 'Australia Photography' started by Jeff R., Aug 28, 2009.

  1. Jeff R.

    Jeff R. Guest

    I have long enjoyed stereo photography, in cross-eyed and parallel
    free-view, anaglyph through coloured glasses and cross-polarised
    projections.

    I was interested to see the "stereo" effect (unintentional) which can be
    seen on some webpages which use strongly contrasting colours.

    Like so:
    http://www.mendosus.com/photography/colour-stereo.html

    Can everyone here see the apparent differences in depth of the coloured text
    on that page?
    Can anyone resolutely *not* see it?

    Does it work with one eye closed?
    (It doesn't for me.)

    More interestingly, can anyone offer a simple, understandable explanation
    for the effect?

    Googling produces some joy, but not much. (Too tight to pay for research
    papers.)

    Anyone think there could be implications here for landscape photography? (Or
    is the effect too gross/unsubtle?)
     
    Jeff R., Aug 28, 2009
    #1
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  2. I'd be very surprised if anyone genuinly couldn't see it as I understand it
    to be the result of fundamental physics and physiology rather than an
    optical trick as much 3d stuff uses. That said the website you've given
    isn't a particularly good one to show it up, it's more obvious when the
    contrasting colours are large and touching or one on top of the other, try
    pink(magenta) on blue.
    It certainly should as the effect is within the eye rather than between eyes
    IYSWIM.
    From (slightly hazy) memory it's caused by chromatic abberation, or
    differential focus, or differential magnification, or differential colour
    (pick a term, I've seen all of them used), of the colours by the simply lens
    of your eye. Photoraphers see this sort of thing a lot in lenses,
    particularly long ones.
    Your eye/brain is not a simple camera and doesn't just record what it sees
    like a camera but rather interprets it to glean information. It's
    (incorrectly) interpreting the chromatic abberation and hence different
    focal points for the colours as distance information.
    Well, it only really happens with fully saturated colours (if you think
    about the explanation you;ll see why) which is why it's common with in
    additive colour systems (things which emit light like monitors) and not
    often seen in subtractive colour systems (paints, books and printed photos)
    although there was a superb album cover in the late 1970's or early 1980's
    which demonstrated it really well with a word written in pink on a blue
    background - I wish I could remember what it was called.
    So if you're in the habit of taking photos of fully saturated pink mountains
    against saturated blue skies look out!

    Cheers,
    Calvin
     
    Calvin Sambrook, Aug 28, 2009
    #2
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  3. Jeff R.

    Doug Jewell Guest

    Likewise, it disappears for me with one eye closed too.
    Others have suggested the different focal length for
    different coloured light, but I don't think it would make
    that much effect, plus if that was the cause it should still
    be present with one eye closed. Also if that was the cause,
    the stereo effect should increase as you get closer (as the
    difference in focus increases), and disappear with distance.
    Whereas I find the opposite, as I get closer the 3D effect
    lessens, as I get further away it increases until I'm about
    3ft from the monitor. I put it down to an effect caused by
    the Bayer filter on the retina, and a slight bug in the
    Brain's raw image convertor and 3D engine. ;-)

    I've observed similar effects with highly saturated slides
    too - eg photos of flowers, green meadows & blue sky.
    Curiously the effect seems to disappear when projected. When
    I first saw the effect with slides, I thought the effect was
    caused by the different colour layers, but then I noticed
    the perception didn't reverse when the slide was turned
    over. And thinking about it more it couldn't be, because on
    a slide the primary colours are made by subtraction from
    multiple layers.
     
    Doug Jewell, Aug 28, 2009
    #3
  4. Jeff R.

    Jeff R. Guest

    "Optical trick" is a bit harsh, I think. All the techniques I am aware of
    serve simply to present a slightly different image to each eye - each image
    offset by (ideally) the spacing of one's eyes.

    Contrasting colours on a black background provide a very real stereo
    illusion, but I can't for the life of me see how it could be presenting
    different (offset) images to each eye.
    Really?
    Is the illusion obvious to you in the first few (red/blue) line groups?

    Not sure I follow what you mean by "large", but I'll give it a go. Stay
    tuned for updates.
    Yes, I follow, but my experience is that the effect *almost completely*
    disappears when I close one eye. I think I'm kidding myself, but I fancy
    there is only a tiny, marginal effect when viewed monocular, but there is
    certainly a huge, easy-to-see effect when viewed binocular.

    Y-e-e-e-es... (trying to figure out how CA would cause a stereo
    illusion...)

    Do you mean:
    The different colours achieve focus at different points (even though the
    source is coplanar), so the brain interprets that difference as a difference
    in depth?
    That makes sense, though it seems contrary to the evidence.
    Would I be aware (consciously) of the differential focus? (Would I be able
    to sense my eyes trying to focus differently?)
    Would/(should?) all the colours appear to be in sharp focus simultaneously?
    (as they demonstrably are)
    Would this effect work monocularly? (I say it doesn't)

    Nice idea.
    I'm sure it's (at least) the germ of the answer. (different wavelengths
    being interpreted differently)
    (sorry - I repeated what you said)
    One of the sources I looked at cited a Van Gogh landscape
    http://astro1.panet.utoledo.edu/~lsa/_color/19_wheatS.jpg
    in which the pastel-blue sky/clouds appear to stand out behind the
    pastel-green fore and mid-ground.
    (from http://astro1.panet.utoledo.edu/~lsa/_color/19_depth.htm - good stuff)

    I don't know if the effect there is down to colour and depth perception, or
    Van Gogh's genius, but either way I do see it... and the colours are pastel,
    not saturated.
    Likewise I recall a story book from my youth that featured bright red and
    blue text on a black background - I found the 3D effect disturbing, even as
    a young'un. Had to run my fingers over the book to be sure it was actually
    flat. (it was)

    Not too many of those round here, so no risk.
    Thanks for your input.
     
    Jeff R., Aug 29, 2009
    #4
  5. Jeff R.

    Jeff R. Guest

    Well, I use blue and red, but not to quibble.

    The purpose of the coloured glasses in anaglyph 3D is (surely) only to
    present different images to each eye - to separate the left image and make
    it visible to the left eye, and vice versa.

    Whilst I freely acknowledge the differential focussing you explained, I
    don't think that has any effect on anaglyphs, which are essentially
    monochrome.

    I've been wrong before, though.
     
    Jeff R., Aug 29, 2009
    #5
  6. Jeff R.

    Jeff R. Guest

    Don't forget our over-active built-in anti-aliasing filters...

    The getting closer/further away effect is what got me started on all this.
    I've just got a new set-top box on my telly, and it has a blue on/off LED.
    When I'm sitting on the lounge, watching the box, (a large proportion of my
    life) the LED appears to be buried deep within the bowels of the box. When
    I look at it close-up, it appears to be flush with the front panel. More
    trickery.

    Of course, the conspiracy theorist in me says that the LED is mounted on
    tracks, and it detects my position and retracts accordingly.
     
    Jeff R., Aug 29, 2009
    #6
  7. Jeff R.

    Jeff R. Guest

    Jeff R., Aug 29, 2009
    #7
  8. Jeff R.

    k Guest

    "Jeff R."


    | Can everyone here see the apparent differences in depth of the coloured
    text
    | on that page?

    yes

    | Does it work with one eye closed?

    yes

    | More interestingly, can anyone offer a simple, understandable explanation
    | for the effect?

    differing points at which the various wavelengths focus (as put well by
    others)
     
    k, Aug 29, 2009
    #8
  9. Calvin Sambrook, Aug 29, 2009
    #9
  10. Yes, I was a bit harsh really they are all tricks in a sense. I didn't mean
    to belittle one or the other.
    By "trick" I kind of mean something which exploits the physiology in order
    to simulate an effect. So presenting two silghtly different 2d images to
    the eyes in a controlled way in order to make the brain think it's viewing a
    3d scene is a trick in that sense, just like presenting a sequence of
    different images in order to trick the eye into thinking it's seeing motion
    is a trick.
    Opps, sorry, I didn't realise that was your work or I would have worded it a
    little less bluntly, I thought you had found that site.
    Your eyes do lots of things you're not aware of. I suspect this effect also
    gets caught up in the stocastic (sp?) movement issue too - do you notice
    that the magenta and red on blue appear to "dance" or "swim" a little on the
    page? Try a big blob of say red on a blue field which covers the whole
    screen.
     
    Calvin Sambrook, Aug 29, 2009
    #10
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