Rear projection

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Rear projection (background projection, process photography, etc.) is one of many in-camera effects cinematic techniques in

for combining foreground performances with pre-filmed backgrounds. It was widely used for many years in driving scenes, or to show other forms of "distant" background motion.

Technique

Actors stand in front of a screen while a projector positioned behind the screen casts a reversed image of the background. This requires a large space, as the projector needs to be placed some distance from the back of the screen. Frequently the background image may initially appear faint and washed out compared to the foreground. The image that is projected can be still or moving, but is always called the plate. One might hear the command "Roll plate" to instruct stage crew to begin projecting.

These so-called process shots were widely used to film actors as if they were inside a moving vehicle, who in reality are in a vehicle mock-up on a sound stage. In these cases the motion of the backdrop film and foreground actors and props were often different due to the lack of camera stabilizing in the filming from the moving vehicles used to produce the plate. This was most noticeable as bumps and jarring motions of the background image that would not be duplicated by the actors.

A major problem with rear projection use was that the image projected on the screen was always slightly less crisp than the action in front of it, an effect which was especially noticeable in sequences where footage with rear projection alternates with non-projection shots.

A major advance over rear projection is

(1968) that the modern version was fully developed. In this case it was used to avoid costly on-location shots in Africa during the opening scenes of the movie, but the effect was also used throughout the film for a variety of shots into the windows of spacecraft. 2001 also used rear projection to produce computer screen effects.

As front projection and

(1994) used the technique extensively throughout to emphasize characters' subconscious motivations.

History

Rear projection was conceived long before its actual usage; however, it was only made possible in the 1930s due to three necessary technical developments. The most important was the development of camera and projector motors that could be linked up for synchronization of their shutters, which were developed out of the unrelated needs of "talking" movies whose timing had to be carefully controlled. Secondly,

beginning to emerge in the late 1920s demanded more powerful projection lamps, which were subsequently available for making the rear projection screen brighter and thus more properly exposed.

In 1930,

In the late 1940s, David Rawnsley introduced the technique in four minor British films, when it was heavily criticized.

Alfred Hitchcock was a master at using process screenshots, mixing them with location shots so that the slight artificiality of the process screen shots does not distract from the action. He used the process to show Cary Grant's character being attacked by a crop duster plane in North by Northwest and throughout the film, but it was criticized when he used it extensively in Marnie.

Fantasy filmmaker

, whereby the rear screen was placed on a miniature set along with stop-motion creatures. Harryhausen figured out a way to synchronize the movement of the miniature figures with the background projection as a way to insert live-action humans in the same scene as the creatures.

See also

• Bipack
• Optical printer "The Hansard Process"
• Schüfftan process
• Traveling matte
• StageCraft

Notes

References

• Clarke, Charles G., A.S.C, Professional Cinematography, Los Angeles, 1964, pp. 153 ff.