Audiences viewing a film presented by Real D are given a pair of plastic 3D glasses. The glasses have circular polarized lenses, each polarized differently. Circular polarization allows much greater head movement than linear polarization without loss of 3D effect or ghost images. This increases audience comfort and helps to mitigate the "3D headache" caused by many 3D systems, especially those relying on film projection.
The movie is projected digitally, with a single Christie, Barco or NEC DLP Cinema projector (other digital projection technologies would work as well if fitted with the proper equipment) at 144 frames per second, six times as fast as a normal movie. Every 1/24 of a second (the projection frame rate for normal 2D movies on film) the two scene views called "right eye" and "left eye" are each shown 3 times (6 flashes of image on the screen matching the 6 times higher projection rate). Due to persistence of vision, the 72 image frames and 72 black frames fed to each eye in a given second should be perceived as a relatively flicker-free image. Due to the low original framerate, the channel separation isn't optimal during horizontal camera movements which results in minor ghosting effects.
In front of the projector lens sits the Z-Screen, an electronic device developed by Lenny Lipton from Stereographics. It inserts a polarizing screen that matches the polarization of either the right lens or left lens of the glasses worn by the audience. When the left-eye-matching Z-Screen is in place, the viewer's right eye sees nothing at all (or almost nothing) while the left eye sees a normal looking frame. For the next frame of the movie, the Z-Screen swaps the polarizing screen to match the right eye lens in the glasses worn by the audience. Now the audience sees nothing (or nearly nothing) with the left eye and a normal but slightly shifted version of the frame in the right eye. The brain knits together the alternating left-right perspectives into a seamless 3D view of the movie scene.
The single projector setup has a number of advantages over previous 3D systems:
- It eliminates most "ghost images" caused by the left eye seeing a bit of the right-eye frames and vice versa.
- It eliminates any form of temporal (time) or spatial misalignment of the left-eye and right-eye frames that plagued previous 3D projection systems relying on movie film. The mechanical jitter of the film in the projector and the poor frame-to-frame matchup generated most of the dull headache 3D side effect caused by the eye muscle strain — along with the much improved, but still slightly flawed, horizontal/vertical polarization system seen for the last 20 years or so in motion simulation amusement rides, IMAX 3D and in limited other venues (Walt Disney World, Disneyland etc.).
The main trouble with polarized 3D systems for movies is a loss of screen brightness. As every other frame is "invisible" to one of your eyes, the image would seem only half as bright, if projected onto a normal screen.
However, this loss of brightness is counteracted to some extent by the fact that theaters must use a silver screen for this type of projection. A normal white matte screen dissipates the polarization of the projected light. The separation of the two images would be immediately lost, without the silver screen.
Fewer than 100 theaters across the US were equipped to show the movie Chicken Little in 3D. Many viewers were not even aware of the 3D version because many people assumed "Disney Digital 3D" refers to the 3D modelling of the CG characters, not the 3D stereoscopic presentation of the movie.[citation needed] The release of Meet the Robinsons was equipped for more than 600 theaters.
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