RealD 3D is a digital stereoscopic projection technology made and sold by
RealD. It is currently the most widely used technology for watching 3D films in
theatres. Worldwide, RealD 3D is installed in more than 26,500
auditoriums by approximately 1,200 exhibitors in 72 countries as of June
2015. Technology
RealD 3D cinema technology is a polarized 3D system that uses circularly
polarized light to produce stereoscopic image projection. The advantage of
circular polarization over linear polarization is that viewers are able to
tilt their head and look about the theater naturally without seeing double
or darkened images. However, as with other systems, any significant head tilt
will result in incorrect parallax and prevent the brain from correctly fusing
the stereoscopic images. The high-resolution, digital cinema
grade video projector alternately projects right-eye frames and left-eye
frames, switching between them 144 times per second. The projector is either a
Texas Instruments' Digital Light Processing device or Sony's reflective
LCOS. A push-pull electro-optical liquid crystal modulator called a ZScreen is
placed immediately in front of the projector lens to alternately polarize
each frame. It circularly polarizes the frames clockwise for the right eye and
counter-clockwise for the left eye. The audience wears circularly polarized
glasses that have oppositely polarized lenses that ensures each eye sees only
its designated frame. In RealD Cinema, each frame is projected three times to
reduce flicker, a system called triple flash. The source video is usually
produced at 24 frames per second per eye, which may result in subtle ghosting
and stuttering on horizontal camera movements. A silver screen is used to
maintain the light polarization upon reflection and to reduce reflection loss
to counter some of the significant light loss due to polarization filter
absorption. The result is a 3D picture that seems to extend behind and in front
of the screen itself. Intensity, dangers & viewing comfort
3D systems for movies using polarized light cause a significant loss of screen
brightness due to the inherent filter absorption. Although the silver screen
used in RealD Cinema is brighter than the standard white screen used for 2D
projection, the ZScreen polarization filter in front of the projector blocks
half of the projected light, then half of the light reflected by the silver
screen is filtered away by the polarized glasses. This results in less than 25%
of the projected light reaching the eyes of the viewer. Conversely, in a standard
2D system, the only significant cause of light loss is absorption by the white
screen. RealD estimates the viewer sees about 35% of the light when viewing
RealD 3D when compared to a similarly projected 2D image on a standard white
screen. The overall effect is that of wearing a pair of slightly darkened
glasses in a standard movie theater, which could be compensated for by using
about 3 times brighter projector lamps if a 100% compensation is intended.
These glasses cannot be used as sunglasses despite their dark tint
because their effect on nearby radiation can be somewhat different. This means
they might not block such wavelengths at all. As a result, the 3D glasses might
expose the retina of the eye to an even higher dose of potential harmful light
components as compared to normal exposure to sunlight as the eye adjusts
the width of its iris opening according to the parts it can detect. Such 3D
glasses might have warnings on their packaging that they will not work as
sunglasses. Some viewers of 3D movies complain of
headaches or nausea during or after viewing. These problems can be caused by
the viewer tilting their head, making it harder for the brain to fuse the two
images. It can also be caused by rapid transitions in the movie between scenes
of very different depth. Consequently, directors and editors of 3D movies
should avoid such transitions. See also
Polarized 3D system List of 3D films
Digital 3D IMAX
Disney Digital 3-D Panavision 3D
Dolby 3D XpanD 3D
MasterImage 3D Lenny Lipton
4DX References
Further reading US patent 7477206, "Enhanced ZScreen
modulator techniques", issued January 13, 2009, assigned to RealD
US patent 6975345, "Polarizing modulator for an electronic stereoscopic display",
issued December 13, 2005, assigned to StereoGraphics Corporation
US patent 5481321, "Stereoscopic motion picture projection system", issued
January 2, 1996, assigned to Lenny Lipton
US patent 4884876, "Achromatic liquid crystal shutter for stereoscopic and
other applications", issued December 5, 1989, assigned to Lenny Lipton
US patent 4792850, "Method and system employing a push-pull liquid crystal
modulator", issued December 20, 1988, assigned to StereoGraphics Corporation
External links Official website
Who is Lenny Lipton? About Inventor and Chief technical officer of RealD through
2008