Rotoscoping is an animation technique that animators use to trace over motion picture footage, frame by frame, to produce realistic action. Originally, live-action movie images were projected onto a glass panel and traced onto paper. This projection equipment is referred to as a rotoscope, developed by Austrian-American animator Max Fleischer. This device was eventually replaced by computers, but the process is still called rotoscoping.
In the visual effects industry, Rotoscoping is the technique of manually creating a matte for an element on a live-action plate so it may be composited over another background. Chroma key is more often used for this, as it is faster and requires less work, but Rotoscoping provides a higher level of accuracy and is often used in conjunction with Chroma-keying. It may also be used if the subject is not in front of a green (or blue) screen, or for practical or economic reasons.
Technique
Rotoscoping has often been used as a tool for visual effects in live-action movies. By tracing an object, the moviemaker creates a silhouette (called a matte) that can be used to extract that object from a scene for use on a different background. While blue- and green-screen techniques have made the process of layering subjects in scenes easier, rotoscoping still plays a large role in the production of visual effects imagery. Rotoscoping in the digital domain is often aided by motion-tracking and onion-skinning software. Rotoscoping is often used in the preparation of garbage mattes for other matte-pulling processes.
Rotoscoping has also been used to create a special visual effect (such as a glow, for example) that is guided by the matte or rotoscoped line. A classic use of traditional rotoscoping was in the original three Star Wars movies, where the production used it to create the glowing lightsaber effect with a matte based on sticks held by the actors. To achieve this, effects technicians traced a line over each frame with the prop, then enlarged each line and added the glow.
History
Predecessors
Eadweard Muybridge had some of his famous chronophotographic sequences painted on glass discs for the zoopraxiscope projector that he used in his popular lectures between 1880 and 1895. The first discs were painted on the glass in dark contours. Discs made between 1892 and 1894 had outlines drawn by Erwin Faber photographically printed on the disc and then colored by hand, but these discs were probably never used in the lectures.
By 1902, Nuremberg toy companies Gebrüder Bing and Ernst Plank were offering chromolithographed film loops for their toy kinematographs. The films were traced from live-action film footage.
Early works and Fleischer's exclusivity
The rotoscope technique was invented by animator Max Fleischer in 1915, and used in his groundbreaking Out of the Inkwell animated series (1918–1927). It was known simply as the "Fleischer Process" on the early screen credits, and was essentially exclusive to Fleischer for several years. The live-movie reference for the character, later known as Koko the Clown, was performed by his brother (Dave Fleischer) dressed in a clown costume.
Conceived as a shortcut to animating, the rotoscope process proved time-consuming due to the precise and laborious nature of tracing. Rotoscoping is achieved by two methods, rear projection and front surface projection. In either case, the results can have slight deviations from the true line due to the separation of the projected image and the surface used for tracing. Misinterpretations of the forms cause the line to wiggle, and the roto tracings must be reworked over an animation disc, using the tracings as a guide where consistency and solidity are important.
Fleischer ceased to depend on the rotoscope for fluid action by 1924, when Dick Huemer became the animation director and brought his animation experience from his years on the Mutt and Jeff series. Fleischer returned to rotoscoping in the 1930s for referencing intricate dance movements in his Popeye and Betty Boop cartoons. The most notable of these are the dance routines originating from jazz performer Cab Calloway in Minnie the Moocher (1932), Snow-White (1933), and The Old Man of the Mountain (1933). In these examples, the roto tracing was used as a guide for timing and positioning, while the cartoon characters of different proportions were drawn to conform to those positions.