Perspective Projection - Transformations and Projections in Computer Graphics - page 132

or displayed). Such picture elements are said to be at the stereo window and are always
comfortable for the eye to watch, regardless of where they are located in the image.
If the red part of a picture element P is placed on the anaglyph to the right of the
corresponding blue part, the brain perceives P as being located in front of the stereo
window. Figure 3.51 shows that this effect requires a large separation of the red and
blue parts. If the red part of a picture element P is placed on the anaglyph to the
left of the corresponding blue part, the brain visualizes P as located behind the stereo
window. Figure 3.51 shows that this can be achieved with only a small separation of
the red and blue parts.
If P is seen in only one of the two eye views (because it is close to a border of the
image), then it is translated to one color only and is not seen in stereo. It may even
confuse the brain if the viewer concentrates on P .
Figure 3.51 also illustrates the effect of moving the viewer closer to and away from
the anaglyph. As we watch an anaglyph from close by, we see the entire image bigger
but with less depth. As we move our head away from the anaglyph, the stereo image
becomes smaller, but the difference between points A and B increases; the image acquires
more depth.

blue

red

B

A

blue

red

blue

red

A

B

blue

red

Figure 3.51: Relative Positions of the Red and Blue Parts (color on page 242).

Page-Flipped Techniques
These techniques require a special monitor screen and special shutter glasses. The screen
switches rapidly between the left-eye and right-eye images. The glasses are triggered
by the monitor hardware to block the right lens when the left-eye image is displayed
and block the left lens when the right-eye image is displayed (Figure 3.52). Thus, the
brain receives the correct image from each eye, and if the images are sent to the brain
at a fast rate, the brain fuses them as usual into a single three-dimensional image. If
the switching rate is low, the brain interprets the signals as a flickering image (still
three-dimensional). The shutters in the glasses are electronic and are normally made
from liquid crystals. The glasses themselves are connected to the monitor (actually, to
the video card) through a special cable or through one of the input/output ports (serial
or parallel). New types of shutter glasses are wireless.