Researchers: Vili Jussila, Kimmo Kaski, and Mikko Sams
In this project an anatomically-based model, which simulates the behaviour of real human face by modeling the actual physical mechanisms responsible for the facial movements, is being developed. The functionality of the head is based on three components: a skin model, a muscle model and a skull model. We have used Magnetic Resonance Images (MRIs) of a real person to obtain the head geometry. An image segmentation procedure is used to convert the volumetric MRI data to a polygonal representation of the head. The skin model is composed of a two-layered lattice of nodes, connected by viscoelastic springs. This imitates the real human skin, which also has a layered structure consisting of epidermis, dermis, sub-cutaneous connective tissue and fascia. Muscles are modeled as straight lines extending from skin to skull surface. A contracting muscle applies an attractive force, in direction of its tail, to the node it is attached to. This force is reflected through the spring lattice to all nearby nodes. The result is that the skin around the attachment point of the muscle is displaced towards the other end of the muscle, see figure 37.
|Figure 37: On the left: Anatomically-based model of a real person's face with geometry obtained from Magnetic Resonance imaging, is shown in its initial form. On the right: The muscles (white lines) at the corners of the mouth have contracted due to the smile of the face.|
A contracting muscle can easily make skin to collapse or sink inside the head. To avoid this, we have implemented a skull model, which restricts the movement of the skin nodes so that they cannot go through the skull. The present skull is a scaled-down version of the head. The movement path of each node is constantly checked against the surface of the skull. If a node penetrates the skull a penalizing force, perpendicular to the surface of the skull, is applied to the node in order push it back.