RealD cinema


RealD Cinema is a digital stereoscopic projection technology made and sold by RealD Inc. It is currently the most widely used technology for watching 3D films in theatres.[1]

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.[2] 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.[2] 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 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.[3]

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 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,[2] 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.[2] 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.[4][5] 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.[6]

See also

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

  • 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
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