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17
Michael Ashikhmin
Computer Animation
Animation is derived from the Latin anima and means the act, process, or result
of imparting life, interest, spirit, motion, or activity. Motion is a dening property
of life and much of the true art of animation is about how to tell a story, show
emotion, or even express subtle details of human character through motion. A
computer is a secondary tool for achieving these goals—it is a tool which a skillful
animator can use to help get the result he wants faster and without concentrating
on technicalities in which he is not interested. Animation without computers,
which is now often called traditional” animation, has a long and rich history of
its own which is continuously being written by hundreds of people still active in
this art. As in any established eld, some time-tested rules have been crystallized
which give general high-level guidance to how certain things should be done and
what should be avoided. These principles of traditional animation apply equally
to computer animation, and we will discuss some of them below.
The computer, however, is more than just a tool. In addition to making the
animator’s main task less tedious, computers also add some truly unique abil-
ities that were simply not available or were extremely difcult to obtain be-
fore. Modern modeling tools allow the relatively easy creation of detailed three-
dimensional models, rendering algorithms can produce an impressive range of
appearances, from fully photorealistic to highly stylized, powerful numerical sim-
ulation algorithms can help to produce desired physics-based motion for partic-
ularly hard to animate objects, and motion capture systems give the ability to
record and use real-life motion. These developments led to an exploding use
of computer animation techniques in motion pictures and commercials, automo-
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414 17. Computer Animation
tive design and architecture, medicine and scientic research among many other
areas. Completely new domains and applications have also appeared including
fully computer-animated feature lms, virtual/augmented reality systems and, of
course, computer games.
Other chapters of this book cover many of the developments mentioned above
(for example, geometric modeling and rendering) more directly. Here, we will
provide an overview only of techniques and algorithms directly used to create and
manipulate motion. In particular, we will loosely distinguish and briey describe
four main computer animation approaches:
Keyframing gives the most direct control to the animator who provides nec-
essary data at some moments in time and the computer lls in the rest.
Procedural animation involves specially designed, often empirical, mathe-
matical functions and procedures whose output resembles some particular
motion.
Physics-based techniques solve differential equation of motion.
Motion capture uses special equipment or techniques to record real-world
motion and then transfers this motion into that of computer models.
We do not touch upon the artistic side of the eld at all here. In general, we can
not possibly do more here than just scratch the surface of the fascinating subject
of creating motion with a computer. We hope that readers truly interested in the
subject will continue their journey well beyond the material of this chapter.
17.1 Principles of Animation
In his seminal 1987 SIGGRAPH paper (Lasseter, 1987), John Lasseter brought
key principles developed as early as the 1930’s by traditional animators of Walt
Disney studios to the attention of the then-edgling computer animation com-
munity. Twelve principles were mentioned: squash and stretch; timing; antic-
ipation; follow through and overlapping action; slow-in and slow-out; staging;
arcs; secondary action; straight-ahead and pose-to-pose action; exaggeration;
solid drawing skill; appeal. Almost two decades later, these time-tested rules,
which can make a difference between a natural and entertaining animation and a
mechanistic-looking and boring one, are as important as ever. For computer ani-
mation, in addition, it is very important to balance control and exibility given to
the animator with the full advantage of the computer’s abilities. Although these
principles are widely known, many factors affect how much attention is being

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