Signal Processing for Stereoscopic and Multi-View 3D Displays - Signal Processing Systems - page 17

HVS. There are two reasons for this; one is that the disparity is too large and the
other is that regions of the scene are close to the frame and are present in one
channel only. If the observer tries to focus on such an area, he or she experiences
diplopia . If that happens for objects with apparent position in front of the screen
it is perceived as the frame violation artifact that is more annoying than diplopic
objects behind the screen [ 46 ] .

3.1 Visibility of Image Distortions

In this chapter we focus on artifacts which affect stereoscopic perception. However,
due to the layered nature of the HVS, stereoscopic artifacts might be induced by
monoscopic distortions, for example blockiness is a monoscopic artifact visible by a
single eye, but can distort display disparity and destroy a binocular depth cue. More
information on artifacts in 3D scenes and their taxonomy can be found in [ 4 , 39 ,
47 - 51 ] .

3.1.1 Viewpoint-Related Distortions

If two views are simultaneously visible by the same eye the effect is regarded as
crosstalk between the views. If an object of the scene is meant to have apparent
depth, its representations in each channel have horizontal disparity. The combination
of crosstalk and disparity creates a horizontally-shifted, semi-visible replica of the
object. The combination of double contours and transparency is interpreted by the
HVS as ghost images , or ghosting [ 47 ] . An example for ghost images is shown in
Fig. 10 a . If the amount of crosstalk is different for each color channel, the shifted
replicas have different colors, as shown in Fig. 10 b . This effect is referred to as color
bleeding . In autostereoscopic displays the visibility of a view is a function of the
observation angle, as shown in Fig. 10 c . The position where one view has maximum
visibility, and the other is maximally suppressed is known as the sweet spot of that
view. The observation zones of the two views are separated by a zone where neither
of the views is predominantly visible. That zone is also known as the stereo-edge .
For autostereoscopic displays, visibility of the ghosting artifacts is proportional
to the crosstalk and has its minimum in the sweet spots and its maximum in
the stereo edge. Subjective visual quality experiments described in Kooi [ 52 ] and
Pastoor [ 4 ] suggest that inter-channel crosstalk of 20% is the maximum acceptable
in stereoscopic image.
Another viewpoint-related distortion is the so-called accommodation-convergence
(A/C) rivalry . On a stereoscopic display the distance to the convergence point can
be different from the focal distance, as shown in Fig. 11 a . This difference is known
as accommodation-convergence mismatch. The accommodation-convergence reflex
drives the eyes to focus at a wrong distance, which causes the objects with
pronounced apparent depth to be perceived out-of-focus. A large discrepancy