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In this example an abstract muscle model controls
facial expressions on a facial geometry. The muscle model provides a
direct linkage to muscle-based coding schemes, such as the Facial
Action Coding Scheme, and is independent of a specific facial
The underlying process is as follows:
- Muscles are described as belonging to one of three primary groups:
Linear, sphincter, and sheet. Each group describes a specific
geometric deformation function emulating muscle action on skin tissue.
- The muscles control parameters are (1) location on bone and skin,
(2) zones of influence, and (3) type of contraction profile (linear,
non-linear). Each muscle functions independently.
- Muscles are then labeled to correspond to Action Units (AU's) in
FACS. Consequently, facial expressions can be created by
orchestrating a sequence of muscle AU contractions.
- Muscle control parameters are then scripted into a keyframe
animation system. At each frame in the sequence, muscles are
contracted that in turn deform the facial geometry. The resulting
geometry is rendered in accordance with viewpoint, light source, and
skin reflectance information.