Visual Discomfort in 3DTV: Definitions, Causes, Measurement, and Modeling - Novel 3D Media Technologies - page 185

optics related errors, filters related errors, and display related errors. Optics errors
are mainly geometry differences between the left and right images, e.g., size
inconsistency, vertical shift, rotation error, magnification, or reduced resolution.
These errors usually occur when shooting or displaying stereoscopic images/videos.
Filters related errors are mainly photometry differences between the two views,
e.g., color, sharpness, contrast. The main error induced by display systems is
crosstalk. Crosstalk produces double contours and is a potential cause of discomfort
[ 19 ]. A study showed that vertical disparity, crosstalk, and blur are most dominant
factors when compared with other binocular factors in visual comfort [ 18 ].
10.2.3.1 Optics Related Errors
The accuracy of the alignment between the two cameras during a stereoscopic
shooting determines the perceptual visual comfort to a large extent. Generally, the
camera misalignments are divided into [ 20 ]:
- Horizontal misalignments;
- Vertical misalignments;
- Torsional misalignments;
- Size and keystone disparity fields.
There are three types of camera misalignment: The pitch and yaw axis horizon-
tally and vertically through the picture plane, while the roll axis coinciding with the
optic axis through the center of the lens. Vertical inconsistency of images caused by
inconsistency of optic axes and errors in the rotational alignment between the two
cameras are known to cause fatigue of eyes. Studies in [ 20 ] indicated that the
relationship between visual discomfort, vertical disparity (in unit of arcmin), and
torsional disparity (degree) are that, in the condition of watching 3D stimuli for 2 s,
vertical disparity about 60 arcmin will induce severe visual discomfort (the five-
level rating scale is: 0—no discomfort, 1— mild, 2—moderate, 3—strong, 4—
severe discomfort). For torsional disparity, 50 will induce strong discomfort.
In the converged camera configuration there is often a distortion called keystone
distortion. It is the phenomenon that in one of the views, the image of the grid appears
larger at one side than the other as shown in Fig. 10.1 [ 21 ]. Studies already showed
that this distortion will induce visual discomfort or even visual fatigue [ 22 , 23 ].
The tolerance of these optics related errors on visual discomfort has been
investigated in [ 24 ] and the results are shown in Table 10.1 .
10.2.3.2 Filters Related Errors
In [ 25 ], the Just Noticeable Difference (JND) thresholds of the visual comfort in
3DTV were investigated psychovisually for seven types of between-eye image
differences, including luminance, gamma, contrast, color temperature, chroma,
hue, and random tone differences. The experimental results showed that: (1) the