Animating Facial Expressions
Platt, S. and Badler, N., Computer Graphics 1981
Abstract
Recognition and simulation of actions performable on rigidly-jointed
actors such as human bodies have been the subject of our research for
some time. One part of an ongoing effort towards a total human
movement simulator is to develop a system to perform the actions of
American Sign Language (ASL). However, one of the "channels"
of ASL communication, the face, presents problems which are not well
handled by a rigid model.
An integrated system for an internal representation and simulation of
the face is presented, along with a proposed image analysis model.
Results from an implementation of the internal model and simulation
modules are presented, as well as comments on the future of computer
controlled recognition of facial actions.
We conclude with a discussion on extensions of the system, covering
relations between flexible masses and rigid (jointed) ones. Applications
of this theory into constrained actions, such as across rigid nonmoving
sheets of bone (forehead, eyes) are also discussed.
Summary
The Facial Action Coding System (FACS) describes the set of all
possible basic actions performable on a human face. Each basic action,
called an action unit (AU), is a minimal action in the sense
that it cannot be broken down into a combination of smaller actions. The
FACS is not graphically oriented, and is considered more difficult for
human notators to learn, but simpler and more straightforward for the
computer to store.
The authors admit the model fails to handle muscle flowing over a bone
sheet ideally because bone structure was not modelled as a solid mass.
Jaw actions and cheek actions such as puffing and sucking are not handled.