P3D Re: Depth perception cues

[Gabriel Jacob <jacob@xxxxxxxxxxxxxx>]

John Roberts gave a pretty comprehensive list of depth perception cues
and then some! 

>Primary sources of human depth perception:
> -binocular stereo: determining the distance (or relative distance) of an
>    object based on the convergence of the eyes, and the disparity (if any)
>    of the two views. Note that you don't have to converge on a particular
>    object to get an idea of its distance (change in disparity with change
>    in convergence is another source of information). (When done properly,
>    the Pulfrich effect produces true binocular stereo, though it is
>    produced by motion.)

Regarding binocular stereo, my understanding is, this relies only on
disparity. Convergence does play a role in depth determination but
only by sensing the eye muscle contractions.

Here is a list of major depth perception cues as outlined in the 
book, "Perception."

 
                     Depth Information
               ______________|______________
              |                             |
          Oculomotor                      Visual
       _______|_______               _______|_______
      |               |             |               | 
Accommodation    Convergence    Binocular       Monocular
                                       _____________|_______
                                      |                     |
                                 Static cues         Motion parallax
                           ___________|___________
                          |           |           |
                    Interposition   Size     Perspective 


P.S. If anyone has been following the heat(ed) ;-) discussion, I
     am replying to John off-list. Hurray!!! 

Gabriel







> - keystoning (nearby objects, not sure - see 970529 T3D discussion)
>     (Premise: the human visual system produces keystoning when viewing
>     nearby objects, and the amount of keystoning is partly a function of
>     the distance to the objects. The issue is whether the brain actually
>     uses this information.)
> - visual cues from the image:
>     - perspective
>     - known shape of an object
>     - known size of an object
>     - hiding of an object by other objects in front of it
>     - multiple-reflection lighting (including reflection from non-specular
>       reflectors)
>     - degree of focus of objects in a scene (not sufficient when used alone
>       to determine depth, but still a useful cue)
>     - distance-related cues such as haze, brightness in a flash photo,
>       texture gradient (variations in perceptible detail with distance),
etc.
> - focal distance of the eyes (which viewers of traditional stereo photos
>     must learn to decouple from convergence) [accommodation]
> - chromatic aberration of the eyes - normally suppressed from conscious
>     perception, but is used to notify parts of the brain on whether the
>     focal distance (accommodation) of the eyes is greater than or less than
>     the distance to the object being viewed
> - depth determined from motion of the point of view (head or camera)
>     examples:
>       - lateral motion of head or camera
>       - rotation of the object being viewed
>       - oscillation of the camera (various patented techniques)
>       - motion of the point of view directly toward or away from the
>           scene being viewed (rate of change in size and angle of view of
>           objects in scene)
> - audio effects, and combination of visual and audio effects
>    (A simple example is determining the distance of a flash of lightning,
>    but the human auditory system is capable of perceiving much shorter
>    distances - there's circuitry in there capable of handling time intervals
>    of hundreds of microseconds, or perhaps better. Humans also use
>    echolocation, usually not consciously - I don't ordinarily notice it,
>    but I find that I can usually walk down a hallway with my eyes closed
>    without bumping into anything, and I can't think of any other
explanation.)
> - kinesthetic senses: your brain knows where in space the articulated parts
>    of your body are.
> - weird stuff like sensing of thermal infrared (The temperature sensitivity
>    of human skin is actually about the same as that of the sensors of pit
>    vipers, though handicapped by being attached to warm flesh. Humans can't
>    image in thermal infrared like pit vipers, but they can detect the
>    proximity of hot or cold objects.) Also detection of electric field of
>    a charged object. Both absolute value and gradient may be distance cues
>    for "touch"-based depth perception.
> - "technology-assisted" depth perception - anything using external devices,
>    for example a blind person's cane, radar, or a GPS receiver.
>
>Note that many of these methods of depth perception are very peripheral
>to stereo photography, but applications such as advanced "virtual reality"
>will require the clever combination of multiple depth perception techniques
>for the most effective creation of realism.
>
>John Roberts
>
>
>
>


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End of PHOTO-3D Digest 3234
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