Polarized 3D glasses create the illusion of
three-dimensional images by restricting the light that reaches
each eye, an example of stereoscopy. To present a stereoscopic
motion picture, two images are projected superimposed onto the
same screen through orthogonal polarizing filters. The viewer
wears low-cost eyeglasses which also contain a pair of
orthogonal polarizing filters. As each filter only passes light
which is similarly polarized and blocks the orthogonally
polarized light, each eye only sees one of the images, and the
effect is achieved. The difficulty arises because light
reflected from a motion picture screen tends to lose a bit of
its polarization. However, this problem is eliminated if a
'silver' or Aluminized screen is used. This means that a pair of
aligned DLP projectors, some polarizing filters, a silver
screen, and a computer with a dual-head graphics card can be
used to form a relatively low-cost (under US$10 000 in 2003)
system for displaying stereoscopic 3d data simultaneously to
tens of people wearing polarized glasses. Such a system, called
a GeoWall, has been used for several years now in the Earth
Sciences thanks to the GeoWall Consortium, with several open
source and commercial packages available.
When stereo images are to be presented to a single user, it
is practical to construct an image combiner, using partially
silvered mirrors and two image screens at right angles to one
another. One image is seen directly through the angled mirror
whilst the other is seen as a reflection. Polarised filters are
attached to the image screens and appropriately angled filters
are worn as glasses. A similar technique uses a single screen
with an inverted upper image, viewed in a horizontal partial
reflector, with an upright image presented below the reflector,
again with appropriate polarizers. Polarizing techniques are
most simply used with cathode ray technology, as polarizers are
used within ordinary LCD screens for control of pixel
presentation - this can interfere with these techniques.
In 2003 Keigo Iizuka discovered an inexpensive implementation
of this principle on laptop computer displays using cellophane
sheets.
Polarized 3D Motion Pictures have been around since
the middle of the 20th century. The so called "3D movie craze"
in the years 1952, through 1955 was mostly offered in theaters
using polarizing projection and glasses. Only a minute amount of
the total 3D films shown in the period used the anaglyph color
filter method. What is new is the use of digital projection, and
also the use of sophisticated IMAX 70mm film projectors, with
very reliable mechanisms. A whole new generation of 3D animation
films are beginning to show up in the theaters, all using some
form of polarization. Polarization is not easily used for home
3D tv or DVD presentation. At this point only anaglyph glasses,
paper or plastic can be used to view the new HD shows at are
beginning to be aired occasionally by NBC and the Discovery
Channel.
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Plastic
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Linear polarized film mounted at opposing 45 degree angles used
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