Chapter 2 Principles of Stereoscopic Depth Perception and ...

2. Principles of Stereoscopic Depth Perception and Reproduction
Figure 2.2: Different perspectives from the left and right eye onto
an object.
separated (on average approximately 6.5 cm) which provides each eye
with a unique viewpoint unto the world (see Figure 2.2). This horizontal
separation causes an interocular difference in the relative projections of
monocular images onto the left and right retina. When points from one
eye’s view are matched to corresponding points in the other eye’s view,
the retinal point to point disparity variation across the image provides information
about the relative distances of objects to the observer and the
depth structure of objects and environments.
The line that can be drawn through all points in space that stimulate corresponding
retinal points for a given degree of convergence is called the
horopter (see Figure 2.3). The theoretical horopter is a circle, known as the
Vieth-Müller circle, which passes through the fixation point and the nodal
points of both eyes. Experimental work has shown that the empirical
horopter lies slightly behind the theoretical horopter, although no satisfactory
explanation has yet been provided to account for this fact. However,
differences between the theoretical and the empirically measured horopter
are small and can usually be ignored for practical purposes (Palmer 1999).
Points which are not on the horopter will have a retinal disparity. Disparities
in front of the horopter are crossed and disparities behind the horopter
are uncrossed. As long as the disparities do not exceed a certain magnitude,
the two separate viewpoints are merged into a single percept (i.e., fusion).
The small region around the horopter within which disparities are fused
is called Panum’s fusional area. Although Figure 2.3 seems to suggest that
Panum’s area is a fixed property of a given retinal region, this is only done
for schematic purposes. The actual size and shape of Panum’s area vary
with the spatial and temporal characteristics of the stimulus, as well as the
procedures used to measure it.
If disparity is large the images will not fuse and double images will be
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