Game Development Reference
In-Depth Information
Figure 11.3 Stereoscopic projection with eyeglasses filtering by colorimetric differentiation
colorimetric quality is important. Stereoscopic vision can be disturbed as the colours
on the screen change slightly with the angle of reflection (Figure 11.3).
Separation by eyeglasses with electronic shutter (active eyeglasses):
These eyeglasses have two liquid crystal screens which shut each eye alternately 60
(or 50) times per second, while the monitor displays images at a frequency of about
100 Hertz. The normal frequency of the monitor is thus doubled to avoid flickering
of images on each eye (25 images per second).
Two procedures can be used to synchronise the shutters with the monitor's dis-
play: The synchronisation is transferred either by a cable connecting the eyeglasses to
the monitor or to the graphic card (a low-cost device for the PC), or by infrared con-
nections (standard device), which offer better flexibility of use. In case of an infrared
connection, the IR receiver on the eyeglasses needs to be positioned in the transmis-
sion cone of the IR transmitter. Otherwise, more than one IR transmitters must be
set, which is indispensable in immersive rooms or when the observer is very close to a
large screen. The major technical difficulty lies in displaying only the desired image at
the right instant without encroachment of images on one another, known as crosstalk
phenomenon (Yeh & Silverstein, 1990; Lipton, 1991). The time of opening (some
milliseconds) and closing (some one-tenths of milliseconds) is not sufficiently small
to completely stop the overlap of images. This creates ghost images which disturb
and stress the observer. Some manufacturers offer a stopper on active eyeglasses which
stops the shutter when the observer looks outside the infrared cone of synchronisation,
which allows monoscopic screens to be viewed.
Separation by polarising eyeglasses (passive eyeglasses):
The technical principle consists of using light polarisation. A liquid crystal screen is
placed in front of each of the two video projectors, which allows polarisation of light
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