Tweening

Inbetweening, also known as tweening, is a process in animation that involves creating intermediate frames, called inbetweens, between two keyframes. The intended result is to create the illusion of movement by smoothly transitioning one image into another. Traditional inbetweening involves the use of a light table to draw a set of pencil and paper drawings. The process of inbetweening in traditional animation starts with a primary artist, who draws key frames to define movement. After the testing and approval of a rough animation, the scene is passed down to assistants, who perform clean-up and add necessary inbetweening. In large studios, assistants usually add breakdowns, which define the movement in more detail. The scene is then passed down to another assistant, the inbetweener, who completes the animation. In small animation teams, animators will often carry out the full inbetweening process themselves. Dick Huemer developed this system in the 1920s, and it has become widely used due to its efficiency. Art Davis is said to be the first Inbetweener. Typically, the key animator does not make drawings for all 24 frames required for one second of film length. In large studios, a specialized inbetweener artist fills in the gaps between the key drawings. Only very fast movements require 24 drawings per second, which is referred to as animating "on ones". Most movements can be done with 12 drawings per second—called animating "on twos", drawing one out of every two frames. When the number of in-betweens is too few, such as four drawings per second, an animation may begin to lose the illusion of the movement altogether. Computer-generated animation is usually animated "on ones." Frame frequency often varies depending on animation style and is an artistic choice. Animation "on twos" has been used for over 100 years; Fantasmagorie (1908), widely considered the first fully animated movie, was animated on twos. Modern animation uses various techniques to adapt frame rates. Slow movements may be animated on threes or fours.