The Real D 3-D system was invented by
Lenny Lipton, an American inventor. It is based on the push-pull electro-optical modulator called the ZScreen.
The technique that Real D uses is comparable to the traditional method of 3-D imaging which uses linearly
polarized glasses. The traditional method works by projecting two differently linearly polarized images onto the same screen, polarized at +45° and -45° from the horizontal, which are then filtered by linearly
polarized glasses worn by the audience. This type of 3-D imaging requires two projectors, and suffers from visible double-imaging if the head is tilted to the side which places the glasses at an inappropriate angle.
Real-D however uses a single projector that alternately projects the right-eye frame and left-eye frame, and
circularly polarizes these frames, clockwise for the right-eye and counterclockwise for the left-eye, using a liquid-crystal screen placed in front of the projector lens. Circularly polarized glasses make sure each eye sees only "its own" picture, even if the head is tilted. The very high framerate, which is 72
fps per eye, makes sure the image looks continuous. In Real D Cinema, each frame is projected three times to reduce flicker, as the source video is usually 24
fps. The result is a seamless 3-D picture that seems to extend behind and in front of the screen itself.
