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
front projection, which uses a special screen material to allow the plate to be projected from the front of the screen. This results in a much sharper and more saturated image. Although the technique had been used experimentally for some time, it was during the filming of
2001: A Space Odyssey (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
bluescreen effects became more widespread and less costly, rear projection has been rendered largely obsolete.
Quentin Tarantino used the process for the taxi ride sequence in
Pulp Fiction (1994).
James Cameron also used rear projection for several special effects shots in
Aliens (1986), including the crash of the
dropship, as well as for several sequences in
Terminator 2: Judgment Day (1991) such as the car escape from the mental hospital and the
T-1000 hijacking the police helicopter; Cameron has been described as one of the few people in Hollywood still able to understand and use process photography as an effective technique. The
Austin Powers film series (1997–2002) frequently used rear projection to help recreate the feel of old spy movies, while
Natural Born Killers (1994) used the technique extensively throughout to emphasize characters' subconscious motivations. == History ==