Introduction - Computer Animation: Algorithms and Techniques - page 10

and usually demands several iterations through multiple steps at various times. Even so, the production
of animation typically follows a standard pattern. First, a preliminary story is decided on, including a
script .A storyboard is developed that lays out the action scenes by sketching representative frames.
The frames are often accompanied by text that sketches out the action taking place. This is used to
present, review, and critique the action as well as to examine character development.
A model sheet is developed that consists of a number of drawings for each figure in various poses
and is used to ensure that each figure's appearance is consistent as it is repeatedly drawn during the
animation process. The exposure sheet records information for each frame such as sound track cues,
camera moves, and compositing elements. The route sheet records the statistics and responsibility for
each scene.
An animatic ,or story reel , may be produced in which the storyboard frames are recorded, each for
as long as the sequence it represents, thus creating a rough review of the timing. Often, a scratch track ,
or rough sound track , is built at the same time the storyboard is being developed and is included in the
animatic. Once the storyboard has been decided on (see Figure 1.5 ), the detailed story is worked out to
identify the actions in more detail. Key frames (also known as extremes ) are then identified and pro-
duced by master animators to aid in confirmation of timing, character development, and image quality.
Associate and assistant animators are responsible for producing the frames between the keys; this is
called in-betweening . Test shots , short sequences rendered in full color, are used to test the rendering
and motions. To completely check the motion, a pencil test may be shot, which is a full-motion ren-
dering of an extended sequence using low-quality images such as pencil sketches. Problems identified
in the test shots and pencil tests may require reworking of the key frames, detailed story, or even the
storyboard.
Inking refers to the process of transferring the penciled frames to cels. Opaquing , also called
painting , is the application of color to these cels.
1.3.1 Principles of animation
To study various techniques and algorithms used in computer animation, it is useful to first understand
their relationship to the animation principles used in hand-drawn animation. In an article by Lasseter
[ 22 ], the principles of animation, articulated by some of the original Disney animators [ 45 ], are related
to techniques commonly used in computer animation. The principles are squash and stretch, timing,
secondary action, slow in and slow out, arcs, follow through and overlapping action, exaggeration,
appeal, anticipation, staging, solid drawing, and straight ahead and pose to pose. Lasseter is a conven-
tionally trained animator who worked at Disney before going to Pixar. At Pixar, he was responsible for
many celebrated computer animations including Tin Toy that, in 1989, was the first computer animation
to win an Academy Award. Whereas Lasseter discusses each principle in terms of how it might be
implemented using computer animation techniques, the principles are organized here according to
the type of motion quality they contribute to in a significant way. Because several principles relate
to multiple qualities, some principles appear under more than one heading.
Simulating physics
Squash and stretch , timing , secondary action , slow in and slow out , and arcs establish the physical basis
of objects in the scene. A given object possesses some degree of rigidity and should appear to have
some amount of mass. This is reflected in the distortion (squash and stretch) of its shape during an