Game Development Reference
uses an active filter, the glasses don't have to actively change to separate the two channels,
so this is another example of passive technology.
The main benefit of polarized systems over anaglyphs is that they provide full-color
viewing and avoid binocular rivalry. This can increase the viewers' comfort when they
are watching feature-length films. The disadvantages are cost and dimness. The glasses
cost much more, and the complexity of projection is increased. It is impossible to create
the effect in static media like print or web pages using standard displays. Also, because
the lens on the projector is blocking out the portions of the light that don't have the
correct polarization, the images appear dimmer to the viewer. This can cause up to 30%
reduction in brightness and is the main point of contention for many directors.
The other display technologies discussed were passive technologies. The projection
carries the two channels and the glasses separate the channels, one for each eye, without
active participation from the glasses. Active technologies require that the glasses do the
work of separating the channels while the display is less important. As the gaming in‐
dustry is more sensitive to adapting 3D display technologies to work with existing
computer monitors or TVs, it has generally focused on active technologies. The most
common active technologies are based on liquid-crystal shutter glasses , or LC glasses.
The LC glasses work by exploiting a property of liquid crystals that causes them to turn
black when a voltage is applied to them. This is the same technology that creates the
eight-segment digits on a simple calculator.
Basically, every other frame being displayed is shown only to one eye, as the LC glasses
cause the lens to darken when the opposing eye's frame is being displayed. To make sure
the glasses are preventing the correct image from being seen by the corresponding eye,
the computer broadcasts a timing signal to the glasses either over a wire or wirelessly.
At the appropriate time, the right eye lens has a voltage applied to it and the entire lens
quickly turns black. As light can enter only the left eye, that eye sees the image on the
screen. As the video being displayed moves to the next frame, this time for the right eye,
the glasses simultaneously are triggered to remove the voltage from the right lens and
apply it to the left lens. With the left lens now darkened, only the right eye sees the right
eye image. As long as this is happening very quickly,—on the order of 60 times per
second per eye, or a total refresh rate of 120 Hz—your brain can't detect that only one
eye is seeing the information on the display at a time. Instead, it interprets it as each eye
seeing distinct images continuously, and as long as the image follows the rules we dis‐
cussed earlier, it interprets it as having depth.