Next: Animation Control
Most facial modeling systems describe facial actions with
either muscle notation or FACS (Facial Action Coding System)
. FACS is based on anatomical studies and denotes any visible
- Libraries of expression and interpolation:
In early models, modeling was done by digitizing sculptures of the face with
various expressions (different lip shapes and expressions) and storing them in
a library . Animation was performed by linear
interpolation between given stored expressions. Such a method is really
tedious and time consuming since it is not automatically adaptable to any
other new model.
- Parametric models:
Some other systems  were based on a set of
parameters which affect not only the size and structure of the model (long
nose, short forehead) but also its expressions (opening of the mouth,
raising eyebrows). The separation between conformation parameters and
expression parameters forces the independence between facial features
and the production of an expression.
- Physically-based models:
These systems describe the skin as an elastic spring mesh where unit actions
are simulated by forces. The deformations are then performed by solving the
dynamic equations . Muscle movement
propagation is intrinsic to the model. Various layers of facial
tissue are integrated . It
succeeds in producing subtle facial actions with realism.
- Integration of additional features:
Texture mapping and hair modeling have been used to enhance realism of the
The consideration of wrinkles and of aging effects  adds much to
the rendering of facial skin and expressions.