Rear projection effect

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Rear projection effect is an in-camera special effects technique in film production for combining foreground performances with pre-filmed backgrounds. Rear projection was devised by Farciot Edouart in 1933. At the time, he was working for Paramount Studios.

The actor stands in front of a screen while a projector positioned behind the screen casts a reversed image of the background. The system was used in many old Hollywood movies, but required a large space to film as the projector had to be placed some distance from the back of the screen. Frequently the background image would appear faint and washed out compared to the foreground.

Alfred Hitchcock used the process successfully to show Cary Grant being attacked by a crop duster plane in North by Northwest, but was criticized when he used it extensively in Marnie.

Innovations such as bluescreen and front projection have rendered rear projection obsolete, though Quentin Tarantino used the process for the taxi ride sequence of Pulp Fiction, and James Cameron used rear projection for several special effects shots within Aliens, including the crash of the Dropship.

Such so-called "process shots" were widely used to film actors as if they were inside a moving vehicle, but who were, in reality, in a vehicle mock-up on a soundstage.

The film that is projected can be still or moving. It is called the "plate." One might hear the command "Roll plate." to instruct stage crew to begin projecting.