The cel is an important innovation to traditional animation, as it allows some parts of each frame to be repeated from frame to frame, thus saving labor. A simple example would be a scene with two characters on screen, one of which is talking and the other standing silently. Since the latter character is not moving, it can be displayed in this scene using only one drawing, on one cel, while multiple drawings on multiple cels will be used to animate the speaking character.
For a more complex example, consider a sequence in which a boy sets a plate upon a table. The table will stay still for the entire sequence, so it can be drawn as part of the background. The plate can be drawn along with the character as the character places it on the table. However, after the plate is on the table, the plate will no longer move, although the boy will continue to move as he draws his arm away from the plate. In this example, after the boy puts the plate down, the plate can then be drawn on a separate cel from the boy. Further frames will feature new cels of the boy, but the plate does not have to be redrawn as it is not moving; the same cel of the plate can be used in each remaining frame that it is still upon the table. The cel paints were actually manufactured in shaded versions of each color to compensate for the extra layer of cel added between the image and the camera, in this example the still plate would be painted slightly brighter to compensate for being moved one layer down.
In very early cartoons made before the use of the cel, such as Gertie the Dinosaur (1914), the entire frame, including the background and all characters and items, were drawn on a single sheet of paper, then photographed. Everything had to be redrawn for each frame containing movements. This led to a "jittery" appearance; imagine seeing a sequence of drawings of a mountain, each one slightly different from the one preceding it. The pre-cel animation was later improved by using techniques like the slash and tear system invented by Raoul Barre; the background and the animated objects were drawn on separate papers. A frame was made by removing all the blank parts of the papers where the objects were drawn before being placed on top of the backgrounds and finally photographed. The cel animation process was invented by Earl Hurd and John Bray in 1915.
Limited animationIn lower-budget productions, shortcuts available through the cel technique are used extensively. For example, in a scene in which a man is sitting in a chair and talking, the chair and the body of the man may be the same in every frame; only his head is redrawn, or perhaps even his head stays the same while only his mouth moves. This is known as limited animation. The process was popularized in theatrical cartoons by United Productions of America and used in most television animation, especially that of Hanna-Barbera. The end result does not look very lifelike, but is inexpensive to produce, and therefore allows cartoons to be made on small television budgets.
"Shooting on twos"Moving characters are often shot "on twos", that is to say, one drawing is shown for every two frames of film (which usually runs at 24 frames per second), meaning there are only 12 drawings per second. Even though the image update rate is low, the fluidity is satisfactory for most subjects. However, when a character is required to perform a quick movement, it is usually necessary to revert to animating "on ones", as "twos" are too slow to convey the motion adequately. A blend of the two techniques keeps the eye fooled without unnecessary production cost.
Animation for television is usually produced on tight budgets. In addition to the use of limited animation techniques, television animation may be shot on "threes", or even "fours", i.e. three or four frames per drawing. This translates to only eight or six drawings per second.
Ryan Larkin's 1969 Academy Award nominated National Film Board of Canada short Walking makes creative use of loops. In addition, a promotional music video from Cartoon Network's Groovies featuring the Soul Coughing song "Circles" poked fun at animation loops as they are often seen in The Flintstones, in which Fred and Barney (along with various Hanna-Barbera characters that aired on Cartoon Network), supposedly walking in a house, wonder why they keep passing the same table and vase over and over again.
Multiplane cameraThe multiplane camera is a tool used to add depth to scenes in 2D animated movies, called the multiplane effect or the parallax process. The art is placed on different layers of glass plates, and as the camera moves vertically towards or away from the artwork levels, the camera's viewpoint appears to move through the various layers of artwork in 3D space. The panorama views in Pinocchio are examples of the effects a multiplane camera can achieve. Different versions of the camera have been made through time, but the most famous is the one developed by the Walt Disney studio beginning with their 1937 short The Old Mill. Another one, the "Tabletop", was developed by Fleischer Studios. The Tabletop, first used in 1934's Poor Cinderella, used miniature sets made of paper cutouts placed in front of the camera on a rotating platform, with the cels between them. By rotating the entire setup one frame at a time in accordance with the cel animation, realistic panoramas could be created. Ub Iwerks and Don Bluth also built multiplane cameras for their studios.
XerographyApplied to animation by Ub Iwerks at the Walt Disney studio during the late 1950s, the electrostatic copying technique called xerography allowed the drawings to be copied directly onto the cels, eliminating much of the "inking" portion of the ink-and-paint process. This saved time and money, and it also made it possible to put in more details and to control the size of the xeroxed objects and characters (this replaced the little known, and seldom used, photographic lines technique at Disney, used to reduce the size of animation when needed). At first it resulted in a more sketchy look, but the technique was improved upon over time.
The xerographic method was first tested by Disney in a few scenes of Sleeping Beauty, and was first fully used in the short film Goliath II, while the first feature entirely using this process was One Hundred and One Dalmatians (1961). The graphic style of this film was strongly influenced by the process. Some hand inking was still used together with xerography in this and subsequent films when distinct colored lines were needed. Later, colored toners became available, and several distinct line colors could be used, even simultaneously. For instance, in The Rescuers the characters outlines are gray. White and blue toners were used for special effects, such as snow and water.
The APT processInvented by Dave Spencer for the 1985 Disney film The Black Cauldron, the APT (Animation Photo Transfer) process was a technique for transferring the animators' art onto cels. Basically, the process was a modification of a repro-photographic process; the artists' work were photographed on high-contrast "litho" film, and the image on the resulting negative was then transferred to a cel covered with a layer of light sensitive dye. The cel was exposed through the negative. Chemicals were then used to remove the unexposed portion. Small and delicate details were still inked by hand if needed. Spencer received an Academy Award for Technical Achievement for developing this process.
Cel overlayA cel overlay is a cel with inanimate objects used to give the impression of a foreground when laid on top of a ready frame. This creates the illusion of depth, but not as much as a multiplane camera would. A special version of cel overlay is called line overlay, made to complete the background instead of making the foreground, and was invented to deal with the sketchy appearance of xeroxed drawings. The background was first painted as shapes and figures in flat colors, containing rather few details. Next, a cel with detailed black lines was laid directly over it, each line drawn to add more information to the underlying shape or figure and give the background the complexity it needed. In this way, the visual style of the background will match that of the xeroxed character cels. As the xerographic process evolved, line overlay was left behind.
Computers and traditional animationThe methods mentioned above describe the techniques of an animation process that originally depended on cels in its final stages, but painted cels are rare today as the computer moves into the animation studio, and the outline drawings are usually scanned into the computer and filled with digital paint instead of being transferred to cels and then colored by hand. The drawings are composited in a computer program on many transparent "layers" much the same way as they are with cels, and made into a sequence of images which may then be transferred onto film or converted to a digital video format.
It is now also possible for animators to draw directly into a computer using a graphics tablet, Cintiq or a similar device, where the outline drawings are done in a similar manner as they would be on paper. The Goofy short How To Hook Up Your Home Theater (2007) represented Disney's first project based on the paperless technology available today. Some of the advantages are the possibility and potential of controlling the size of the drawings while working on them, drawing directly on a multiplane background and eliminating the need of photographing line tests and scanning.
Though traditional animation is now commonly done with computers, it is important to differentiate computer-assisted traditional animation from 3D computer animation, such as Toy Story and Ice Age. However, often traditional animation and 3D computer animation will be used together, as in Don Bluth's Titan A.E. and Disney's Tarzan and Treasure Planet. Most anime still use traditional animation today. DreamWorks executive Jeffrey Katzenberg coined the term "tradigital animation" to describe films produced by his studio which incorporated elements of traditional and computer animation equally, such as Spirit: Stallion of the Cimarron and Sinbad: Legend of the Seven Seas.
Interestingly, many modern video games such as Viewtiful Joe, The Legend of Zelda: The Wind Waker and others use "cel-shading" animation filters or lighting systems to make their full 3D animation appear as though it were drawn in a traditional cel style. This technique was also used in the animated movie Appleseed, and cel-shaded 3D animation is typically integrated with cel animation in Disney films and in many television shows, such as the Fox animated series Futurama.
RotoscopingRotoscoping is a method of traditional animation invented by Max Fleischer in 1915, in which animation is "traced" over actual film footage of actors and scenery. Traditionally, the live action will be printed out frame by frame and registered. Another piece of paper is then placed over the live action printouts and the action is traced frame by frame using a lightbox. The end result still looks hand drawn but the motion will be remarkably lifelike. Waking Life is a full-length, rotoscoped animated movie, as is American Pop by Ralph Bakshi. The popular music video for A-ha's song "Take On Me" also featured rotoscoped animation, along with live action, in addition, Kanye West's music video for his song Heartless, in homage to American Pop is fully rotoscoped. In most cases, rotoscoping is mainly used to aid the animation of realistically rendered human beings, as in Snow White and the Seven Dwarfs, Peter Pan, and Sleeping Beauty.
A method related to conventional rotoscoping was later invented for the animation of solid inanimate objects, such as cars, boats, or doors. A small live action model of the required object was built and painted white, while the edges of the model were painted with thin black lines. The object was then filmed as required for the animated scene by moving the model, the camera, or a combination of both, in real time or using stop-motion animation. The film frames were then printed on paper, showing a model made up of the painted black lines. After the artists had added details to the object not present in the live-action photography of the model, it was xeroxed onto cels. A notable example is Cruella de Vil's car in Disney's One Hundred and One Dalmatians. The process of transferring 3D objects to cels was greatly improved in the 1980s when computer graphics advanced enough to allow the creation of 3D computer generated objects that could be manipulated in any way the animators wanted, and then printed as outlines on paper before being copied onto cels using Xerography or the APT process. This technique was used in Disney films such as Oliver and Company (1988) and The Little Mermaid (1989). This process has more or less been superseded by the use of cel-shading.
Related to rotoscoping are the methods of vectorizing live-action footage, in order to achieve a very graphical look, like in Richard Linklater's film A Scanner Darkly.
Live-action hybridsSimilar to the computer animation and traditional animation hybrids described above, occasionally a production will combine both live-action and animated footage. The live-action parts of these productions are usually filmed first, the actors pretending that they are interacting with the animated characters, props, or scenery; animation will then be added into the footage later to make it appear as if it has always been there. Like rotoscoping, this method is rarely used, but when it is, it can be done to terrific effect, immersing the audience in a fantasy world where humans and cartoons co-exist. Early examples include the silent Out of the Inkwell (begun in 1919) cartoons by Max Fleischer and Walt Disney's Alice Comedies (begun in 1923). Live-action and animation were later combined to successful effect in features such as The Three Caballeros (1944), Anchors Aweigh (1945), Song of the South (1946), Mary Poppins (1964), Bedknobs and Broomsticks (1971), Heavy Traffic (1973), Coonskin (1975) Pete's Dragon (1977), Who Framed Roger Rabbit (1988), Rock-a-Doodle (1992), Cool World (1992), The Pagemaster (1994) Space Jam (1996), and Looney Tunes: Back In Action (2003). Other significant live-action hybrids include the music video for Paula Abdul's hit song "Opposites Attract" and numerous television commercials, especially for breakfast cereals marketed to children. This technique was also recently used for the Geico commercial starring Foghorn Leghorn.
Special effects animationBesides traditional animated characters, objects and backgrounds, many other techniques are used to create special elements such as smoke, lightning and "magic", and to give the animation in general a distinct visual appearance.
Notable examples can be found in movies such as Fantasia, Wizards, The Lord of the Rings, The Little Mermaid, The Secret of NIMH and The Thief and the Cobbler. Today the special effects are mostly done with computers, but earlier they had to be done by hand. To produce these effects, the animators used different techniques, such as drybrush, airbrush, charcoal, grease pencil, backlit animation or, during shooting, the cameraman used multiple exposures with diffusing screens, filters or gels. For instance, the Nutcracker Suite segment in Fantasia has a fairy sequence where stippled cels are used, creating a soft pastel look.