Anatomy based animation of facial expressions

This study presents a new physics based facial expression animation system based on anatomic data. Proposed system consists a face model and a new facial expression animation generation algorithm.The proposed system is a Mass-Spring-Damper (MSD) system. It consists single layer face model HIGEM and a set of facial muscles which are placed anatomically correct places. Non-linear viscoelastic characteristics of the human skin isapproximated with non-linear springs. The set of muscles triggers facial expressions.HIGEM does not include a skull to support the facial mesh, so it tends to collapse under muscle forces. A new algorithm proposed to prevent this. This algorithm uses back and forward projections for re-defining the muscle forces. Anotherproblem of MSD systems is individual element collapse under large forces. This is addressed with Edge Repulsion (ER) approach.Dynamics of the face is modelled with a quasi-implicit Ordinary Differential Equation (ODE). The regions of the face affected by the facial muscles were computed and marked offline in previous works to speed up the animations. It requiresoffline re-calculation whenever the activation level of the muscles or facial mesh topology changes. Thus, a new generic stack based approach which works at runtime is proposed.The proposed system is tested with eight facial expressions; happy, sad, angry, feared, surprised, disgusted, disgusted anger and happy surprise. Elapsed times for the facial expressions vary with number of contracting muscles, their region of inuence, and the time value for each timestep.