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418 17. Computer Animation
sequence until the end, pose-to-pose action, also known as keyframing,ismuch
more suitable for computer animation. In this technique, animation is carefully
Key frames (created first)
Time
Straight ahead order of frame creation
Figure 17.3. Keyfram-
ing (top) encourages de-
tailed action planning while
straight-ahead action (bot-
tom) leads to a more spon-
taneous result.
planned through a series of relatively sparsely spaced key frames with the rest
of the animation (in-between frames) filled in only after the keys are set (Fig-
ure 17.3). This allows more precise timing and allows the computer to take over
the most tedious part of the process—the creation of the in-between frames—
using algorithms presented in the next section.
Almost any of the techniques outlined above can be used with some reason-
able amount of exaggeration to achieve greater artistic effect or underscore some
specific property of an action or a character. The ultimate goal is to achieve some-
thing the audience will want to see, something which is appealing. Extreme com-
plexity or too much symmetry in a character or action tends to be less appealing.
To create good results, a traditional animator needs solid drawing skills.Analo-
gously, a computer animator should certainly understand computer graphics and
have a solid knowledge of the tools he uses.
17.1.4 Animator Control vs. Automatic Methods
In traditional animation, the animator has complete control over all aspects of the
production process and nothing prevents the final product to be as it was planned
in every detail. The price paid for this flexibility is that every frame is created by
hand, leading to an extremely time- and labor-consuming enterprise. In computer
animation, there is a clear tradeoff between, on the one hand, giving an animator
more direct control over the result, but asking him to contribute more work and,
on the other hand, relying on more automatic techniques which might require
setting just a few input parameters but offer little or no control over some of the
properties of the result. A good algorithm should provide sufficient flexibility
while asking an animator only the information which is intuitive, easy to provide,
and which he himself feels is necessary for achieving the desired effect. While
perfect compliance with this requirement is unlikely in practice since it would
probably take something close to a mind-reading machine, we do encourage the
reader to evaluate any computer-animation technique from the point of view of
providing such balance.
17.2 Keyframing
The term keyframing can be misleading when applied to 3D computer animation
since no actual completed frames (i.e., images) are typically involved. At any
given moment, a 3D scene being animated is specified by a set of numbers: the