Chapter 2 Principles of Stereoscopic Depth Perception and ...

2. Principles of Stereoscopic Depth Perception and Reproduction
2.3.1 Stereoscopic displays
Stereoscopic displays (i.e., those using viewing aids) can be time-parallel,
with both left and right eye views appearing simultaneously, or timemultiplexed,
where the left and right eye views are shown in rapid alternation
and synchronised with a liquid crystal (LC) shuttering system which
opens in turn for one eye, while occluding the other eye. Time-multiplexed
systems make use of the fact that the human visual system is capable of
integrating the constituents of a stereo pair across a time-lag of up to 50 ms
(Pastoor & Wöpking 1997). Because of the rapid alternation of right and
left eye images, the display will need to run at twice the frame rate of the
original sequence material. For example, to display a 60 Hz sequence a 120
Hz display is required. When image extinction is not fast enough, due to
the persistence of CRT phosphors, cross-talk may occur. This is an imperfect
separation of the left and right eye views which can be perceptually
very annoying. An example of a time-multiplexed system is the StereoGraphics
CrystalEyes system, which has become popular for use with
stereoscopic desktop workstations, and is also frequently used for large
projection spaces, such as the CAVE (Cruz-Neira et al. 1993).
For time-parallel stereoscopic displays several multiplexing methods have
been used, based on either colour, polarization or location. In colourmultiplexed,
or anaglyph, displays the left and right eye images are filtered
with near-complementary colours (red and green for Europe, red and blue
for the USA). The observer is required to wear colour-filter glasses to separate
the images. This well-known and inexpensive method has been used
for stereoscopic cinema and television, and is still popular for viewing
stereoscopic images in print (magazines, etc.), since the approach readily
lends itself to the production of hard copies. A serious limitation of
this method is that colour information is lost since it is used as a selection
mechanism. Only limited colour rendition is possible through the mechanism
of binocular colour mixture.
Polarization-multiplexed displays separate left and right eye images by
means of polarised light. Left and right output channels (monitors or projectors)
are covered by orthogonally oriented filters, using either linear
or circular polarization. The observer needs to wear polarised glasses to
separate the different views again. This system offers good quality stereoscopic
imagery, with full colour rendition at full resolution, and very little
cross-talk in the stereo pairs (Pastoor & Wöpking 1997). It is the system
most commonly used in stereoscopic cinemas today. The most significant
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