An inverse dynamics approach to face animation

Michel Pitermann (1) , Kevin Munhall (1)

1 Department of Psychology

Muscle-based models of the human face produce high quality animation but rely on recorded muscle activity signals or synthetic muscle signals that are often derived by trial and error. This paper presents a dynamic inversion of a muscle-based model Lucero and Munhall, 1999 that permits the animation to be created from kinematic recordings of facial movements. Using a nonlinear optimizer Powell's algorithm , the inversion produces a muscle activity set for seven muscles in the lower face that minimize the root mean square error between kinematic data recorded with OPTOTRAK and the corresponding nodes of the modeled facial mesh. This inverted muscle activity is then used to animate the facial model. In three tests of the inversion, strong correlations were observed for kinematics produced from synthetic muscle activity, for OPTOTRAK kinematics recorded from a talker for whom the facial model is morphologically adapted and finally for another talker with the model morphology adapted to a different individual. The correspondence between the animation kinematics and the three-dimensional OPTOTRAK data are very good and the animation is of high quality. Because the kinematic to electromyography EMG inversion is ill posed, there is no relation between the actual EMG and the inverted EMG. The overall redundancy of the motor system means that many different EMG patterns can produce the same kinematic output.

Mots clés: face modeling; inversion; biomechanical modeling; face animation

Mots clés: modele de visage; modele biomecanique; animation faciale

Domaines: Biomécanique [physics.med-ph]; Multimédia [cs.MM]; Interface homme-machine [cs.HC]; Linguistique

Michel Pitermann, Kevin Munhall. An inverse dynamics approach to face animation. Journal of the Acoustical Society of America, 2001, 110 (3), pp.1570-1580. ⟨hal-00142945⟩