Rear projection

A filmmaking technique in which a background image is projected onto a translucent screen behind actors, allowing foreground action and a pre-recorded scene to be filmed together.

Front projection: A film technique that projects a background image onto a reflective screen from the camera side. It places projector and camera on the same side of the screen, unlike rear projection.
Process photography: A filmmaking method that combines foreground action with a separately photographed background during filming. Rear projection became one of the principal forms of this broader technique.
Car process shot: A film shot in which actors inside a stationary or controlled vehicle appear to travel through a projected background. Rear projection made moving scenery possible without filming actors on a road.
Chroma key: A compositing technique that removes a selected color from an image and replaces it with another image. It combines foreground and background in postproduction rather than photographing a projected image in camera.
Translucent screen: A screen that transmits diffused light while scattering it enough to display an image. It lets projected backgrounds appear behind performers while the camera films from the front.
Traveling matte: A compositing method that isolates moving foreground subjects to combine them with another image. It offered an alternative to projecting backgrounds behind actors during the original camera exposure.
Driving scene: A dramatic scene depicting a character operating or riding in a vehicle. Projected roads and landscapes let dialogue and close-ups be filmed safely on a controlled set.
Blue screen: A blue background used for chroma-key compositing in film and television. It became a practical alternative when rear projection could not convincingly match the scene.
Optical axis: The line through the centers of an optical system that defines its principal direction. Keeping projector, screen, and camera aligned helps preserve background geometry.
The Thief of Bagdad (1940 film): A 1940 British fantasy film directed by Michael Powell, Ludwig Berger, and Tim Whelan. Its effects work provides a notable early showcase of elaborate in-camera background techniques.

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