Introduction - Computer Animation: Algorithms and Techniques - page 15

Recording background and mood music can be added after the fact and usually require no precise
timing with the action. All the sounds other than voice are added after the live action or animation is
recorded.

1.4 Computer animation production
Computer animation production has borrowed most of the ideas from conventional animation produc-
tion, including the use of a storyboard, test shots, and pencil testing. The storyboard has translated
directly to computer animation production, although it may be done on-line. It still holds the same func-
tional place in the animation process and is an important component in planning animation. The use of
key frames, and interpolating between them, has become a fundamental technique in computer
animation.
While computer animation has borrowed the production approaches of conventional animation,
there are significant differences between how computer animation and conventional animation create
an individual frame of the animation. In computer animation, there is usually a strict distinction among
creating the models; creating a layout of the models including camera positioning and lighting; spec-
ifying the motion of the models, lights, and camera; and the rendering process applied to those models.
This allows for reusing models and lighting setups. In conventional animation, all of these processes
happen simultaneously as each drawing is created; the only exception is the possible reuse of back-
grounds, for example, with the multilayer approach.
The two main evaluation tools of conventional animation, test shots and pencil tests, have coun-
terparts in computer animation. A speed/quality trade-off can be made in several stages of creating
a frame of computer animation: model building, lighting, motion control, and rendering. By using
high-quality techniques in only one or two of these stages, that aspect of the presentation can be quickly
checked in a cost-effective manner. A test shot in computer animation is produced by a high-quality
rendering of a highly detailed model to see a single frame, a short sequence of frames of the final prod-
uct, or every n th frame of a longer sequence from the final animation. The equivalent of a pencil test can
be performed by simplifying the sophistication of the models used, by using low-quality and/or low-
resolution renderings, by eliminating all but the most important lights, or by using simplified motion.
Often, it is useful to have several representations of each model available at varying levels of detail.
For example, placeholder cubes can be rendered to present the gross motion of rigid bodies in space and
to see spatial and temporal relationships among objects. “Solids of revolution” objects (objects created
by rotating a silhouette edge at certain intervals around an axis and then defining planar surfaces to fill
the space between these silhouette slices) lend themselves quite well to multiple levels of detail for a
given model based on the number of slices used. Texture maps and displacement maps can be disabled
until the final renderings.
To simplify motion, articulated figures 7 can be kept in key poses as they navigate through an envi-
ronment in order to avoid interpolation or inverse kinematics. Collision detection and response can be
selectively “turned off” when not central to the effect created by the sequence. Complex effects such as
smoke and water can be removed or represented by simple geometric shapes during testing.

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Articulated figures are models consisting of rigid segments usually connected together in a tree-like structure; the connec-
tions are revolute or prismatic joints, allowing a segment to rotate or translate relative to the segment to which it is connected.