Some of the first instances of commercial computer animation were traditionally drawn animated sequences that used computer assistance. This could be in the form of the computer producing "in-betweens" or images that connect two similar images input by the artist (thus allowing the artist to draw fewer individual images). Computer assisted animation was first used in an animated feature film in Disney's "The Great Mouse Detective" in 1986. A scene in the film takes place inside of a clock, and the complex mechanical gears were actually rendered in a computer as wire-frame graphics before being transferred to cells, where they were united with the other elements of the scene. Similar techniques were used by Disney in later films such as "Beauty and the Beast" (1991), "Pocahontas" (1995) and "Tarzan" (1999) to reproduce smooth, complex motion in the traditional, two-dimensional animated style.
Most modern computer animation uses a motion control system that the animator manipulates to create an object, and then move that object through a series of poses. This produces the motion that will result in the final moving image. The first motion control animation was done with scripting systems such as ASAS (Actor Script Animation System). In these scenarios, the animator is a computer programmer who writes code in a computer language to produce an object and impart movement to that object. As computer animation evolved, more interactive systems were developed to allow animators to interact with their images and objects through a more abstract interface. Codes are now written automatically, based on input that the animator makes using a visual interface and manipulating the subject with a mouse, keyboard or other input device.
Computer animation is also used in place of older techniques of film animation. Since the early days of the cinema, animated elements have been added to photographed images. Other elements, such as models or painted backdrops, were also used and had to be painstakingly paired with the live-action footage. This involved a lengthy optical process in which the various elements were re-photographed several times in order to be composited together into a single image. Because of the complexity of the process, special effects were costly and seldom used in great quantity by all but the most highly financed films.
Computer generated imagery changed all that, allowing filmmakers to use blue or green screens to select portions of the film that can later easily be removed by computers and replaced with an image from another source, either a photograph or a piece animation. Computer animation compositing is even a function in many consumer-level video editing programs.
Motion capture is a type of computer animation that has gained much interest in recent years. It relies on small sensors that are placed on actors at various points around their body. The actors perform and their motions are captured by a camera that can locate the sensors and trace their movement. This motion can then be transferred to a computer-designed figure who will move in precisely the same way as the actors did.
Motion capture is significant for its bridging the gap between traditional film-making methods and new technology. Motion capture performances are often discussed in terms of their realism or emotion, just as live-action performances would be. Some notable examples of motion capture include Gollum in the "Lord of the Rings" films, the 2005 version of "King King" and the entire cast of 2007's "Beowulf."
One final type of computer animation is Flash animation. Flash animations are named for the Flash program from Adobe with which they are produced, though today there are other programs that also allow animators to create "flash" animation. Despite its limitations in terms of movement and style, Flash is inexpensive to produce and therefore growing in popularity. Flash animations are often used in advertising and are common as video content on websites.
Flash animation uses vectors to produce movement. This means that rather than containing an object in each of its states as it moves between points, the program simply stores relevant information about the characteristics of the object itself and then produces a mathematical formula that describes its movement. This process is useful for creating computer animations when file size is an issue, as in Web distribution or when animating on a personal computer.