Signal Processing for Stereoscopic and Multi-View 3D Displays - Signal Processing Systems - page 4

redundancy-free replica of the scene. In a typical use case a redundancy-free replica
is also a visually indistinguishable representation of the scene under the use
case constraints. Failure in creating redundancy-free and visually-indistinguishable
replica leads to visible distortions. In order to avoid this one needs to know which
light properties are important and which scene features are relevant for perceiving
thescenein3D.

2.1.1 Visual Perception of Depth

Vision in general can be separated into two parts—visual perception and visual
cognition. In studies of human vision, visual perception and properties of early
vision are subjects of anatomy and neurophysiology [ 1 , p.2, 2 ] , and visual cognition,
as a higher level brain function, is a subject of psychology [ 1 , p. 387, 3 ] .
Visual perception involves a number of optical and neural transformations. The
eye can change its refractive power in order to focus on objects at various distances.
The process is known as accommodation and the refractive power is measured
in diopters. The light entering the eye is focused onto the retina which contains
photosensitive receptors tuned to various spectral components (frequencies). The
density of the photoreceptors has its maximum close to the optical center of the
eye. The area with the highest photoreceptor density is known as the fovea. There
are four types of photoreceptor cells—rods, L-cones, M-cones and S-cones—which
allow detection of light with wavelengths between 370 and 730 nm. The cones can
be thought of (to a crude approximation) as sensitive to red, green and blue color
components of the light. The rods are responsible for the low-light vision and are
generally ignored in HVS modeling. Rather than perceiving continuous spectrum,
the HVS encodes the color information as a combination of three color components;
the process is known as color perception . The combination of the iris controlling the
amount of light entering the eye, and the sensitivity adaptation of the retina allow the
eye to work over a wide range of intensities (between 10 − 6 and 10 8 cd/m 2 ). The eye
is sensitive to luminance difference (i.e. contrast) rather than absolute luminance
values. This visual property is known as light adaptation .However,theHVShas
different contrast sensitivity for patterns with different density and orientation [ 1 ] .
The ability to perceive visual information through two distinctive eyes is known
as binocular vision . The eyes of a human are separated horizontally and have dis-
tance between pupils (also known as interpupilar distance , IPD) of approximately
65 mm on average [ 2 ] . Such positioning allows each eye to perceive the world
from a different perspective, as shown in Fig. 1 . The luminance, color and contrast
perception occur in each eye separately and the visual information is fed through the
optical nerve to the so-called lateral geniculate nucleus (LGN) [ 1 ] . The LGN de-
correlates the binocular information and produces a single, fused representation of
the scene. The fused image appears as if observed from a point between the eyes and
is called cyclopean image . The point, which is projected in the fovea of each eye, is
known as the point of convergence . The observer can control the visual fixation
point though the extraocular muscle system . If an object is around the point of