Linear subspaces for facial expression recognition

This paper presents a method for the recognition of the six basic facial expressions in images or in image sequences using landmark points. The proposed technique relies on the observation that the vectors formed by the landmark point coordinates belong to a different manifold for each of the expressions. In addition experimental measurements validate the hypothesis that each of these manifolds can be decomposed to a small number of linear subspaces of very low dimension. This yields a parameterization of the manifolds that allows for computing the distance of a feature vector from each subspace and consequently from each one of the six manifolds. Two alternative classifiers are next proposed that use the corresponding distances as input: the first one is based on the minimum distance from the manifolds, while the second one uses SVMs that are trained with the vector of all distances from each subspace. The proposed technique is tested for two scenarios, the subject-independent and the subject-dependent one. Extensive experiments for each scenario have been performed on two publicly available datasets yielding very satisfactory expression recognition accuracy.