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Figure 11.2 Principle of vision with auto-stereoscopic screen with lenticular network
moving his head. In this case, the vision is more similar to natural vision. But this
change of point of view is possible only in a small portion of space (Figure 11.2).
Various types of screens have been tested. Flat screens are currently used because it
is easier to align the pixel columns with the cylindrical lenses. This is the main technical
difficulty of auto-stereoscopic screens, mainly large size screens.
The main advantage of auto-stereoscopic screens is that the user does not need
to wear any eyeglasses (very useful in aeronautics and mainly in public places for an
immediate vision). However, as a result of the possibility of multiple points of view,
reducing the resolution of images at least by 2 (or 4 or 8) is the main inconvenience.
The moiré of the auto-stereoscopic screen degrades the image quality a little. The main
disadvantage is that the observer must be in a specific zone, relatively restricted, so
that both of his eyes perceive a good image. Alioscope, a French invention, uses the
auto-stereoscopic principle with a lenticular network, placed in front of a flat screen. Separation by eyeglasses
Separation by colorimetric differentiation:
The old and well-known procedure that uses two-tone eyeglasses (anaglyph procedure)
is an easy and low-cost solution for creating stereoscopic vision on a sheet or on a
screen. Each eye sees only one of the two images of different colours, red and cyan
(complementary colour of red), thanks to the two filters on the pair of eyeglasses. This
procedure now has little appeal, as the manufacturers offer active eyeglasses for PC
compatibles at an affordable price or autostereoscopic screens.
However, Barco Company has recently updated this procedure (Infitec procedure
under license from DaimlerChrysler). Each eye of the observer receives a different
filtered image on the Red, Green and Blue (RGB) components of the colour spectrum.
This can be achieved by putting a pair of eyeglasses having two different colorimetric
filters and by providing two video projectors, displaying the images on a large screen. It
is possible to make 4 differentiations on the filters and ask two observers to see a scene
with two different points of view. Then the problem arises of the quality of restitution
of the virtual objects' exact colours. This can be troublesome in applications where the
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