How 3D cinema works

Stereo vision is caused by the fact that each of our eyes sees the world from a different point of view. Our brain processes these two different, although similar, pictures into a single image of the visual world. Thus we can perceive which objects are close and which are more distant.

3D movies are captured with two parallel running film or digital cameras which - just like our eyes - are positioned a few centimeters apart, so each camera records a slightly different perspective.

At the theatre, these two images are projected synchronously with two film or video projectors or alternately at high frequency with a suitable D-Cinema projector. To the naked eye the resulting picture is blurred, but with 3D glasses you will see perfectly focused stereoscopic pictures. Each single eye-glass lens lets only pass one of the two projected pictures. Thus the right eye can only see the images recorded by the right camera, and the left eye can only see the “left image”. The brain interprets these two lightly different pictures as one three-dimensioned image, and the events on the screen seem to be almost tangible - a perfect 3D effect!

Digital 3D cinema

With D-Cinema, exhibitors can easily bring the third dimension to their cinema screens. All you need for a crystal-clear stereoscopic projection is one digital projector with the DLP Cinema® technology from Texas Instruments, such as our DCP Digital Cinema Projectors. These can combine the incoming two data streams delivering the right eye and left eye images to a single output signal. The 3D subframes are stringed together and projected in rapid succession. At the same time the D-Cinema projector doubles or triples the refresh rate to 96 or 144 Hz, which reliably prevents flickering pictures.

Thanks to the DCI specifications for digital cinema, all common D-Cinema servers are "3D ready" and thus able to feed the 3D subframes synchronously to the projector. In order to ensure the right eye and left eye subframes are perceived seperately by the viewers, an additional set of 3D components is required. The industry offers different 3D systems to achieve a proper channel separation.

DLP Cinema®-projectiors project stereoscopic images one after another

Digital 3D projcetion systems

Filter Wheel System (Dolby): A rotating filter wheel assembly integrated in the D-Cinema projector slightly dislocates the position of the light waves for the RGB primary colors of the right eye and left eye pictures. The filter lenses of the corresponding passive 3D glasses are tuned to the resultant color shift, so each eye can only perceive one of the two projected 3D subframes.

Polarisation Filter Systems (RealD, Masterimage): An active polarisation filter (RealD) or polarisation filter wheel (Masterimage) is placed in front of the D-Cinema projector lens. This filter aligns the light waves of the stereoscopic subframes in a different way. The lenses of the passive 3D glasses are polarized accordingly so they let only pass the right pictures or the left eye pictures. As a conventional matte white screen would neutralize this polarisation, a silver screen is required.

Shutter Glasses System (XpanD): The D-cinema projector signals a special sync box whether a right eye or a left eye picture is projected at the moment. The sync box controls the active shutter-glasses by infrared communication, dimming their lenses alternately so only one eye at a time can look at the screen. If the picture for the left eye is projected, the right glass becomes opaque, and vice versa.