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A key frame is a reference point in an animation providing information about the position, shape, and size of the subject. These frames help animators control the transition from one position to another, and also impose limits on the timing to determine the speed of the animation. Both traditional and computer animation rely on the use of key frames to outline the critical components of an animated sequence, and an animation may include any number of these references, depending on length.
In a simple example of a key frame, an animator could want to create a demonstration of a dot drifting from one side of the screen to the other. This would require two drawings to show the beginning and end position of the dot. With computer animation, the computer may be able to perform the rendering to show the dot in transition, using parameters set by the animator. More frames can create a smoother transition, while fewer frames and staggered timing may make it jerky.
Hand-drawn animations require animators to draw in each frame between the key frames. This can be a time consuming process. Historically, head animators focused on the key frame production, and passed their work on to assistants who handled the filler frames and any necessary adjustments. Traditional animation of this type is rare in most production facilities, although students may experiment with it as they learn about animation techniques and practices. Restoration of animated films may require insertion of new frames to replace damaged or missing frames, for example.
Users can control the blocking, the movement within an animation, with the use of a series of key frames. Each frame shows where people and objects should be positioned during the scene, and provides data about who and what should move. Creating and adjusting each key frame can require extensive labor, and requires continuity checks for consistency. A table, for example, should not move between key frames unless the angle is changing or a moving table is part of the action. Assistants may review frames for inconsistencies and other problems that might make the animation look abnormal.
Computer animation provides a number of options for people to use as they develop a key frame and animation sequence. This technology can be used for activities like filling in the background on a movie and making animated people and animals appear consistent with random, natural movements. Post-production companies can specialize in computer-generated textures and effects to add to film, or entirely animated pieces for shorts as well as advertisements and feature-length productions.