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animatronics: puppets of human, animal, or creature form controlled by an operator manually or remotely via electronic or radio control.

blue-screen photography (also green-screen): technique of filming a subject in front of a blue- or green-screen; the blue or green background is then removed through optical or digital processes, allowing the subject, or element, to be isolated for compositing with another element. Often characters are filmed with a blue-screen in order to place them in a different scene, or on a miniature set.

composite: to combine two or more individual images onto one piece of film by photographic or digital means. Early compositing was accomplished in the camera by masking part of the scene when filming, rewinding the film and removing the matte and shooting again to expose the previously masked portion. The photographic technology of the optical printer revolutionized visual effects in the 1920s. In the 1990s, digital compositing is commonplace, in which multiple film images are scanned into the computer, combined digitally, and output to a single piece of film.

computer generated imagery (CGI): Images created with the use of a computer. Also called computer graphics (CG), computer animation, or digital animation.

element: one photographic image, which will be composited with others to create a complete visual effects shot.

gag (also trick): a special effect.

glass shot: background scenery painted on glass that is positioned in front of the camera and filmed so that it appears to be part of the scene.

hanging miniature: a miniature suspended in front of the camera. When viewed through the lens, it appears to be part of a structure in the scene. In the Ben Hur (1925) chariot race scene, only the lower part of the coliseum was built. The upper tiers, including thousands of tiny "spectators" mounted on rods to allow them to stand, was a hanging miniature.

matte (also mask): Early filmmakers created in-camera composites by covering part of the lens with a mask while filming, or placing a sheet of glass with a blacked-out area between the camera and the scene, to prevent a portion of the film from being exposed. The cameraman would then rewind the film, and shoot again with the mask removed and the previously exposed area covered, thus combining two images in one shot. In "The Playhouse," (1921), Buster Keaton used this method to put himself on-stage as nine different characters. A stationary matte marks off a static defined area; a travelling matte follows the silhouette of a moving character or object and changes shape from frame to frame.

matte painting: painting of elaborate background scenery that can be composited with live action or miniatures. They were originally painted on glass, but artists now often create them with the computer.

mechanical effects (also called practical or physical effects): special effects created on-set in front of the camera which may not require additional photographic manipulation. Includes pyrotechnics, animatronic creatures, make-up effects, flying with wires.

motion-control camera: a camera controlled by a computer, which can be programmed to precisely duplicate the same movement repeatedly. With motion control, multiple elements can be filmed in exactly the same way, allowing the images to be aligned for compositing.

multiple exposure: the photographing of two images onto the same piece of film.

optical printer: device consisting of a projector and camera with lenses facing each other; in the process called compositing, two or more pieces of film with elements of a scene are placed in the projector and photographed together onto a new piece of film in the camera.

pyrotechnics: the controlled use of incendiary materials to create explosions, fires, and smoke.

rear projection: a previously filmed background scene is projected behind actors on a screen in a studio, to create the illusion that they are on location.

stop-motion animation: technique in which a miniature puppet is moved incrementally through a range of motions and photographed one frame at a time with each movement. When the filmed scene is run at the conventional film speed of 24 frames per second, the illusion that the creature is moving is created. "King Kong," animated by Willis O'Brien, is an acclaimed example of the technique.

substitution shot: trick shot in which the camera is stopped and the actors freeze while an object or actor is exchanged for another. In "The Execution of Mary Queen of Scots," the actors froze while a dummy was substituted for the actress just as the ax is poised to fall; the camera was then re-started to capture the "beheading."

trick (also trick shot or gag): a special effect

visual effects (also called optical or photographic effects): special effects achieved with the aid of photographic or digital technology, occurring after the principal photography, or main shooting, of a film. Includes miniatures, optical and digital effects, matte paintings, stop-motion animation, and computer-generated imagery (CGI).

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