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.
Because RealD 3D uses a single projector, it suffers a brightness disadvantage. The system causes "significant light loss"; 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 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 (Liquid crystal on silicon). 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 (total 48 frames/s), 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 inherent losses by the polarization filters. The result is a 3D picture that seems to extend behind and in front of the screen itself.
They are not for use as sunglasses despite their dark tint. As a matter of fact, the 3D technology is even worse than standard glasses, and posts warnings on packaging that they are not safe for use as sunglasses.
Viewing comfort 
3D systems for movies using polarized light cause a loss of screen brightness due to the inherent filter absorption. The polarization filter in front of the projector blocks half of the projected light, and then split again one half for each eye, resulting in only 25% of the projected light reaching the eye. This is compensated somewhat by the silver screen which boosts the brightness to about 35% of the original. 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 brighter projector lamps.
Some viewers of 3D movies complain of headaches or nausea during or even after viewing. Those problems can be caused by the viewer tilting their head, making it harder for the brain to fuse the two images (due to parallax mismatch between the eyes and the cameras). 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
- Disney Digital 3-D
- Panavision 3D
- Dolby 3D
- XpanD 3D
- MasterImage 3D
- Lenny Lipton
- Verrier, Richard (2009-03-26). "3-D technology firm RealD has starring role at movie theaters". Los Angeles Times. Retrieved 2011-02-05.
- Cowan, Matt. "Real D 3D Theatrical System". European Digital Cinema Forum. Retrieved 2009-03-28.
- Cowan, Matt. "Presentations (technical)". RealD Media Room downloadable files. Retrieved 2009-03-28.
- Watt, Nick (2009-12-19). "Will 'Avatar' Make Viewers Nauseous? The 3D Effects in Blockbuster Movie 'Avatar' Are Claimed to Be 'Vomit Inducing'". ABC news.
- "How to avoid getting a 3D headache while watching Avatar". Shadowlocked. 2009-12-21.
- Needleman, Rafe (2009-06-18). "3D means new rules for directors".
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
|Wikimedia Commons has media related to: RealD cinema|
- RealD website
- RealD Cinema page
- RealD Theater Locator
- Dolby Digital 3D vs Real D / Master image systems Video Technology Blog
- Who is Lenny Lipton? About Inventor and Chief technical officer of RealD through 2008