Inferring Facial Action Units with Causal Relations

A system that could automatically analyze the facial actions in real time have applications in a number of different fields. However, developing such a system is always a challenging task due to the richness, ambiguity, and dynamic nature of facial actions. Although a number of research groups attempt to recognize action units (AUs) by either improving facial feature extraction techniques, or the AU classification techniques, these methods often recognize AUs individually and statically, therefore ignoring the semantic relationships among AUs and the dynamics of AUs. Hence, these approaches cannot always recognize AUs reliably, robustly, and consistently. In this paper, we propose a novel approach for AUs classification, that systematically accounts for relationships among AUs and their temporal evolution. Specifically, we use a dynamic Bayesian network (DBN) to model the relationships among different AUs. The DBN provides a coherent and unified hierarchical probabilistic framework to represent probabilistic relationships among different AUs and account for the temporal changes in facial action development. Under our system, robust computer vision techniques are used to get AU measurements. And such AU measurements are then applied as evidence into the DBN for inferencing various AUs. The experiments show the integration of AU relationships and AU dynamics with AU image measurements yields significant improvements in AU recognition.