Traditional Drawn or Puppet Animation

In [1], Thomas and Johnston enumerate the principles that guided the Disney animators as they created feature films and shorts. These principles address the tricks that the animator can use to create a caricature of real world physical motion. The principles can be applied to living characters or inanimate objects to give the drawn animation a life like quality. Lasseter, who worked at Disney under Johnston, later wrote about how the principles can be applied by the artist to computer animation [2][3].

Many of these principles guide the animator in ways to make the character appear to think and respond to its environment. These include staging, exaggeration and appeal. These principles rely heavily on the artist's ability to "act" the animated character. These principles are very difficult to encode in software and have only been recently tackled [4].

Some of the principles such as squash and stretch, arcs, slow in slow out, overlapping action, anticipation, follow through and timing are closely related to the physical constraints that guide real motion.

Anticipation is the preparation before the main motion that tells the audience what to expect. An example from Thomas and Johnston is the character coiling himself up like a spring before running. Squash and stretch is the emulation of the elastic properties of the object being animated. It is worthy of note that most characters in drawn animation undergo large amounts of squash and stretch even in the "rigid" links of their limbs. The principle of arcs comes out of the observation that most natural figure motions follow curved paths through space. Follow through and timing are both related closely to the mass and inertia of the figure. The higher the mass, the slower the start and the longer it takes to slow down. The character's motion is perceived as more natural if it does not suddenly stop at the end, there must be follow through. Overlapping action is the interleaving of two or more motions so that one does not stop before the other has begun.

Direct control is achieved easily in traditional animation. The artist simply draws the figure in the desired position. In the case of a three dimensional puppet, the animator moves the limb to its next position by direct manipulation.

These are some things that the traditional animator takes for granted that should be available in a computer graphics animation program. How do the three methods of computer animation address these control issues?