3-D movies is the short name for a Stereoscopic 3-D film, a illusionary motion picture technology which has its roots based in stereoscopic photography. Based on the principle of depth perception (three-axis rule, also known as the third dimension), stereoscopic photography creates the 3 dimensional illusion by shooting the image at two slightly different angles. The glasses through which such images appear as 3-D are created on the cross-eyed view technique, the same principle as that of binoculars.
Such a film is generally shot using two perspectives which are not too different from each other. This can either be done using two cameras or a camera with dual lenses set a uniform distance and angle from each other. The two angles can also be computer generated graphics.
Since there are two sets of films, special projection hardware is used to display the film. The film appears as a single image with the help of special glasses. Such hardware is not only available for the 70mm movie screen, but can be used for television broadcasting too. There are several new technologies which use alternative techniques cut down on costs. One such technique is ‘RealD 3D cinema‘ technology.
Single Camera Projectors
‘RealD 3D cinema’ method uses a light based technique known as the circular polarization for creating the stereoscopic image-type projection of the film. It means that using this projection system, the film need not be shot using two lenses. This reduces the cost considerably as the film can be relayed as both a 3-D projection as well as a 2-D projection, because the film is shot as 2-D but projected as 3-D. Since it’s not a color imbalance but a light based simulation, the glasses for the two are different too.
Stereoscopic photography creates an image known as anaglyph. Although two lenses are used, a single image is created. These are generally superimposed through two color filters, one in red the other in cyan. Thus when a 3-D image is projected using a stereoscopic projector system, glasses with one red and another cyan lens create the cross-eyed effect, to make the image appear as one. Although this technique has become obsolete for movie viewing, it is still largely used for Blu-ray disk or DVD movies and for promotional purposes.
RealD Projector Glasses
The RealD projector alternates images 144 times per second between the right and left eye frames. This is the crux of the circular polarization method. Since the camera has a single scene shot at normal 24 frames per second, the RealD projector displays 48 frames per second to create the 3-D effect. The silver screen on which the film is finally projected absorbs the excessive light generated because of the high frame rate display. Thus the glasses used for such a viewing have a slightly dark set of lenses which absorb the unwanted light thrown by the projector lamp. If there are rapid transitions between scenes, viewers may experience motion sickness or nausea.