weighting depth cues

[T3D Peter Abrahams <telscope@xxxxxxxxxx>]

The many cues to information on relative depth of an object in a visual
field are discussed in Howard & Rogers, _Binocular Vision and Stereopsis_.  
A distinction is drawn between spatial cues arranged in parallel, where any
one cue is sufficient (direction of a sound), or in series, where all cues
are needed (judging relief of a surface from motion parallax of the
movement of the head).  In a parallel cue system, the cues can conflict
with each other.  
This abstract overview of depth cues is carried to a considerable length on
pages 435-440.  Cues are averaged, traded, & summed; there is dominance &
dissociation; and classification of cue interactions is proposed.  Several
models of cue interactions are described, based on cues of disparity (edge
based & intensity based disparity), motion, luminance, texture, & perspective.
Page 438, one study included the view that there is no consistent theory
for these phenomenon, but instead a 'bag of tricks which provides
particular solutions in particular situations'.  
Page 448, disparity-perspective interactions, is more relevant to
discussions of stereo photography, and includes Schriever's 1924 study
using stereo photographs with reversed disparity, which showed that depth
was judged more from perspective than disparity.  
Page 456, Wheatstone, 1838, simple line stereograms viewed pseudoscopically
show reversed depth, but appear correct if they are of familiar objects.
Photographs contain many monocular cues to depth, and do not necessarily
show the same effects.  Some studies show that familiarity with the object
affects pseudoscopic viewing, and others indicate otherwise.  

There is a very large amount of relevant material elsewhere in this book,
but the overall impression is that the 'bag of tricks' idea is more
consistently accurate than a dogma. 
It certainly seems that this is an extremely complicated phenomenon with
large variances between individuals and considerable hazard to the generalist.
_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx
the history of the telescope, the microscope,
    and the prism binocular


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