Graphics Programs Reference
In-Depth Information
when image L is displayed, only the left eye of the viewer sees the display and when
image R is displayed, only the right eye sees the screen.
y
lens
lens
R
L
(a)
(b)
(c)
Figure 3.58: Autostereoscopic Display With Light Bars.
The ideal way to achieve such optical synchronization is to use a liquid crystal
(LCD) display. This type of display does not generate light and has to be illuminated
from behind. Two special light sources and a Fresnel lens are now placed behind the
display. Each light source is a narrow vertical rectangle (a light bar) that illuminates
the display from a different direction, thereby causing the light from the display to be
sent in a different direction. Figure 3.58b illustrates this configuration as seen from
above. The viewer has to be positioned at the center of the eye box. (The eye box is
simply a region in space, not a screen or a device.). When light from bar x reaches the
lens and the display, the image from the display is seen only by the viewer's right eye.
A little later, light bar x is turned off and light bar y is turned on, causing the image
from the display to shift to the left (in the figure, it is shifted down) and be seen only
by the viewer's left eye.
Figure 3.58c shows how this idea can be extended to more than two images. Imagine
six cameras positioned in front of a scene. The cameras are set precisely at the same
height, they are parallel, and are separated horizontally by seven cm. Six images are
sent to the computer and are time-multiplexed by it to the display. Six light bars are
synchronized with the images, such that each image is directed by the display to a
different area in the eye box. The viewer can now shift his head left and right from area
to area within the eye box and can see the scene in three dimensions from five positions
with the correct parallax.
Unfortunately, this ideal arrangement is currently impractical because of the fol-
lowing reasons:
1. The images must be sent to the LCD display at a high rate in order to create
the illusion of a single, three-dimensional image. In a system with six images, if we
want to send each image to the display 60 times a second, we need a refresh rate of
6
60 = 360 Hz. Unfortunately, the refresh rate of current LCD displays is low. A
practical autostereoscopic display must therefore use a high-speed CRT.
2. It is di cult to arrange six cameras at the same height while also keeping
them parallel and separated by the right distance. The autostereoscopic display that is
currently developed by Deeplight uses two cameras and a special, proprietary algorithm
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