RealD
RealD is a digital 3D polarization system for 3D films that, unlike some older methods, does not require two projectors. Another advantage of the RealD system is that existing DLP projectors can be used - but supplemented by a projector attachment, 3D glasses and special silver-coated screens (see section Screen ).
The RealD-3D system is based on an electro-optical modulator , called ZScreen, which was devised by the US inventor Lenny Lipton .
The RealD system is used in 233 cinemas in Germany.
technology
The technology that RealD uses is comparable to the traditional 3D projection method that uses linear polarization . In the traditional method, two linearly polarized images are projected onto the same screen, polarized at an angle of + 45 ° or −45 ° to the horizontal. The spectators' glasses polarizing at the same angles ensure that each eye only sees the correct image. This type of 3D projection requires two projectors and has the disadvantage that ghost images occur if the viewer tilts their head to one side and the angle of the polarization filters of the projector and glasses no longer exactly match.
RealD, however, only needs a single projector, which alternately projects the right and left image and uses circularly polarized light. An LCD element in front of the projection lens polarizes the light clockwise for one eye and counterclockwise for the other. A combination of a λ / 4 retardation plate and a polarization filter sits in the spectator's glasses. The retardation plate converts the circularly polarized light into linearly polarized light. Different orientations of the retardation plates (which are perpendicular to one another and each form an angle of ± 45 ° with the horizontal) in the spectacle lenses ensure that right-hand circularly polarized light is converted into horizontally linearly polarized light only in one lens. In the other glass, circularly polarized light is converted into horizontally linearly polarized light. The following polarizers on the eye side of the glasses are both aligned horizontally (transmission direction). This ensures that each eye only sees its own image, even when the viewer tilts his head. The very high frame rate of 72 frames per second and the eye ensure a flicker-free image. Since the video signal delivers only 24 frames per second, with RealD each frame is projected three times to avoid a flicker effect.
canvas
In order to be able to use the polarization process, a silver-coated canvas is required that reflects the light. When projecting onto a conventional white screen, the polarization of the light is lost because the light is scattered on the surface of the screen. As a rule, however, conventional cinemas are equipped with a white screen.
The problem of the additionally required silver screen can be avoided if instead of polarization the alternating projection of the images for the left and right eye is used (i.e. not RealD is used). By using shutter glasses that (controlled by an infrared signal) alternately switch one and then the other lens to dark, the conventional screen can be used, but the shutter glasses used here are orders of magnitude more expensive. Even when using interference filter technology, there is no need to use a silver screen.
See also
Web links
- RealD homepage (English)
- Article about Real-D technology (PDF, 508 kB)
Individual evidence
- ^ Theater Locator. In: RealD - The New 3D. RealD, accessed on May 25, 2013 (English, Country: Germany).