Signal Processing for Stereoscopic and Multi-View 3D Displays - Signal Processing Systems - page 5

a b

Fig. 1 Binocular geometry: ( a ) horopter for a given point of convergence and ( b ) zone of clear
vision for a given point of focus

convergence the HVS can fuse its projections into each eye into a cyclopean image.
Since eyes perceive the scene from different perspectives the projections of an object
around the point of convergence are not identical. The existence of two different
retinal images is called binocular disparity [ 2 ] . The difference between retinal
images allows the brain to deduct information about the relative depth between
different points of interest. The ability of the brain to deduct depth information from
retinal disparity is known as stereovision .
All points that are projected onto identical places in each retina (relative to
the fovea) can be fused by the HVS. For a given point of convergence there are
points which are projected with identical offset relative to each fovea, as shown
for points “A” and “B” in Fig. 1 a . The set of all points which are projected onto
matching retinal positions is called the horopter . The theoretical horopter coincides
with the circle which passes through the point of convergence and the center of
each eye's lens, as shown in Fig. 1 a . That circle is also known as Vieth-M uller
circle . However, the horopter derived through subjective experiments (also called
the empirical horopter ) does not fully coincide with the theoretical one. Around the
horopter there is a region of points at which projections can be fused by the HVS.
That region is known as Panum's area and outside of this, binocular depth is still
perceived but objects are seen as doubled. The experience of seeing double objects
is known as diplopia [ 1 ] .
When eyes focus on a point the refractive power of each eye changes in order
that the projections of that point appear in focus in each retina, as seen in Fig. 1 b .
Close to the point of focus there is a larger area where objects are perceived in
focus. The area is known as zone of clear vision and its size depends on the
distance to the point of focus and the size of the iris. In order to speed-up the