Muscle Based Modeling

The goal of the research is to devise an efficient and accurate model of the human face and to develop a notational system to encode actions. This notation should be rich enough to make computer recognition possible.
It seems to be very convenient to have a separate notation for body and action representation:

Given the two separate notations, the authors propose a system that recognizes facial actions on a given face (using a camera) and simulate that face:

Both the high-level and the low-level representation (before and after the Internal Model Manipulator) can be used to store the face for further use, modification or reconstruction on another computer.

Design of the System

The authors have chosen the tension-net as structure-based representation. They believe it is the most usable (and general) approach since it is a naturally-based system. The FACS has been chosen as action-based notation as it is very compatible with the tension-nets.
The FACS - Tension-net approach offers the following features:



The basic structures used are:


When a fiber contracts, a force is applied to its fiber point. The direction of this force is towards the bone point. The displacement of the fiber point is relative to the elasticity of the flesh. The force is propagated through all the arcs adjacent to that point.
To simulate a muscle or a set of muscles, the sets of all fibers of all these muscles is considered.


When a force can be applied to a muscle as stated above, animation can be achieved simply by applying a force f/n n times. The animation becomes smoother as n increases, but at the same time, the computational cost becomes higher, so a tradeoff has to be found.



The choice of the representations was backed-up by the fact that the solution of several expected problems came naturally. The problem of one AU masking the existence of another (first smile, then raise cheek vs raise cheek: since the cheek is raised during a smile, the second action of the first case should not have any effect) is handled naturally as a result of the way skin elasticities are handled. A second problem involving the creation of bulges, wrinkles and furrows was again handled very will (these are all caused by two forces pushing points towards each other.


Several problems were not handled at the time of writing:
Back to home..