Game Development Reference
Figure 24-9. Parallax barrier
As shown in this figure, older screens used the slits to bar certain pixels from being seen
by placing them above the screen. Newer screens like the one on the Nintendo DS place
the barrier lower than the pixels, but before the backlight. This prevents your eyes from
receiving the light from those pixels that are being shaded by the solid spaces between
the slits. This results in a clearer image and a wider viewing angle.
Speaking of viewing angle, if the method works because your eyes aren't in the same
spot, it is obvious that if you move your whole head then you'll also be seeing a different
set of pixels. This is the drawback: that there is a relatively small area called the “sweet
spot” that the user must position his head relative to the screen to perceive the 3D effect.
It makes it inappropriate for movies, as only a portion of the seats would be in the sweet
spot, but it is in use for handhelds where only one user will be viewing the screen at any
given time. Another drawback is that because the slits are eliminating half the pixels
from each eye, the system reduces the effective pixel count by one-half. This causes a
reduction in resolution that can be countered by even higher pixel density.
Another method very similar to the parallax method is replacing the layer of slits with
a series of lenses that direct light from certain pixels to a certain eye. These are called
lenticular lenses and are illustrated in Figure 24-10 .