A rotoscope is a device that enables animators to trace live action movement, frame by frame, for use in animation. It might be called a clumsy forerunner to digital motion capture. The device was invented by Max Fleischer, who used it in his series "Out of the Inkwell" starting around 1914. Fleischer used his brother Dave Fleischer , dressed in a clown outfit, as the live-film reference for the character Koko the Clown. The rotoscope was used in a number of later Fleischer cartoons as well, most notably the Cab Calloway dance routines in three Betty Boop cartoons from the early 1930s, and the animation of Gulliver in Gulliver's Travels.
Rotoscopy is decried by some animation purists, but has often been used to good effect. When used as an animator's reference tool, it can be a valuable time-saver. Walt Disney and his animators employed it carefully and very effectively in Snow White, primarily used in the animation of Prince Charming. By contrast, Ralph Bakshi used rotoscope quite slavishly in The Lord of the Rings and Wizards - by so doing, he could produce animation without hiring animators.
The rotoscope has also been used as a tool for special effects in live action movies. By tracing an object, a silhouette (called a matte) can be created that can be used to create an empty space in a background scene. This allows the object to be placed in the scene. Such a technique, of creating mattes by hand, was used in the movie 2001: A Space Odyssey. Because of this special-effects usage, in computer graphics, to rotoscope is to create an animated matte indicating the shape of an object or actor at each frame of a sequence, as would be used to composite a CGI element into the background of a live action shot.