RealD 3D cinema technology uses circularly polarized light to produce stereoscopic image projection. Circular polarization technology has the advantage overlinear polarization methods in that viewers are able to tilt their head and look about the theater naturally without a disturbing loss of 3D perception, whereas linear polarization projection requires viewers to keep their head orientation aligned within a narrow range of tilt for effective 3D perception; otherwise they may see double or darkened images.
The high-resolution, digital cinema grade video projector alternately projects right-eye frames and left-eye frames 144 times per second. The projector is either a Texas Instruments' Digital Light Processing device or Sony's reflective liquid crystal display. 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 counterclockwise for the left eye. The audience wears spectacles with oppositely circularly polarized lenses to ensure each eye sees only its designated frame, even if the head is tilted. 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. Asilver screen is used to maintain the light polarization upon reflection and to reduce reflection loss to counter 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
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