Process Photography

a form of motion-picture special-effects photography based on combining several previously filmed images by projecting them onto a single screen or by combining a single image with that of a live scene, mock-up, or illustration located in front of the screen. The images are projected frame by frame, that is, with pauses, or at the usual speed (24 frames per second) using special motion-picture projectors. Process photography makes it possible to incorporate in a single picture objects filmed at different times and places and in different scale relationships and spatial settings, as well as to supplement an image with illustrations, diagrams, captions, or arrows.

As a rule, frame-by-frame projection and filming are done on small screens, for example, 24 × 30 cm. The projected image is filmed from a reflecting screen by the front-projection method or from a translucent screen by the back-projection method. When projected frame by frame, the image can also be rephotographed directly from the film in the aperture of the projector (optical-printing method). Various mattes are used to prevent double exposure of sections of the frame (seeTRAVELING-MATTE METHOD and FIXED-MATTE METHOD).

Process photography is widely used in 24-frame-per-second motion-picture and television filming for combining a live scene with an image on large screens, for example, 5 × 7 m; this makes it possible to film outdoor scenes on a studio set, for example, by creating a moving background outside the windows of automobiles, trains, or aircraft.