Learning prototypes and similes on Grassmann manifold for spontaneous expression recognition

Video-based spontaneous expression recognition is a challenging task due to the large inter-personal variations of both the expressing manners and the executing rates for the same expression category. One of the key is to explore robust representation method which can effectively capture the facial variations as well as alleviate the influence of personalities. In this paper, we propose to learn a kind of typical patterns that can be commonly shared by different subjects when performing expressions, namely “prototypes”. Specifically, we first apply a statistical model (i.e. linear subspace) on facial regions to generate the specific expression patterns for each video. Then a clustering algorithm is employed on all these expression patterns and the cluster means are regarded as the “prototypes”. Accordingly, we further design “simile” features to measure the similarities of personal specific patterns to our learned “prototypes”. Both techniques are conducted on Grassmann manifold, which can enrich the feature encoding manners and better reveal the data structure by introducing intrinsic geodesics. Extensive experiments are conducted on both posed and spontaneous expression databases. All results show that our method outperforms the state-of-the-art and also possesses good transferable ability under cross-database scenario.