A process of photographing a series of still images, each slightly different from the other, it gives the effect of movement when projected at the rate of about 24 frames per second. The Walt Disney Studios, creators of Donald Duck, Mickey Mouse, etc., used a system of painting each figure in a cartoon and the elements of the background or scene on separate sheets of transparent celluloid that were superimposed in the animation camera. When a character moved in these particular scenes, only the character had to be repainted, which saved much re-drawing. Walt Disney, persuaded that animation could be taught as a scientific method, listed the qualifications of a skilled animator: Good draftsmanship, knowledge of caricature, appreciation of acting, ability to think up gags, and understanding of mechanical aspects and detailed routine. Source: Fern and Kaplan, "Viewpoints: The Library of Congress Selection of Pictorial Treasures", 187; Bob Thomas, "Walt Disney", p. 124.