12.2AnalyzingMultiviewDisplays 181
Figure 12.2. Stereo rendering techniques that require wearing glasses. From left to right, anaglyph
glasses, polarized glasses, shutter glasses, and head-mounted displays.
■ Anaglyph glasses. These are based on multiplexing color channels. The two
views are filtered with different colors and then superimposed to achieve the
final image.
■ Head-mounted displays (HMDs). These are based on displaying both views
synchronously to separate display surfaces, typically as miniaturized LCD,
organic light-emitting diode (OLED), or CRT displays.
■ Shutter glasses. These are based on temporal multiplexing of the two views.
These glasses work by alternatively closing the left or right eye in sync with
the refresh rate of the display, and the display alternately displays a different
view for each eye.
■ Polarized glasses. With passive and active variants, these glasses are based
on presenting and superimposing the two views onto the same screen. The
viewer wears a special type of eyeglasses that contain filters in different ori-
entations.
While these displays require special hardware, another type of 3D display,
called an autostereoscopic display, creates the 3D effect without any special eye-
glasses. Autostereoscopic displays operate by emitting a different image toward
each eye of the viewer to create the binocular effect. This is achieved by aligning
an optical element on the surface of the screen (normally an LCD or OLED) to
redirect light rays for each eye. A composite image that superimposes the two
views is rendered by the display subpixels, but only the correct view is directed
to the corresponding eye.
There are two common types of optical filter, a lenticular sheet and a parallax
barrier. A lenticular sheet consists of small lenses having a special shape that re-
fract the light in different directions. A parallax barrier is essentially a mask with
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