View and scale invariant action recognition using multiview shape-flow models

Actions in real world applications typically take place in cluttered environments with large variations in the orientation and scale of the actor. We present an approach to simultaneously track and recognize known actions that is robust to such variations, starting from a person detection in the standing pose. In our approach we first render synthetic poses from multiple viewpoints using Mocap data for known actions and represent them in a conditional random field (CRF) whose observation potentials are computed using shape similarity and the transition potentials are computed using optical flow. We enhance these basic potentials with terms to represent spatial and temporal constraints and call our enhanced model the shape, flow, duration-conditional random field (SFD-CRF). We find the best sequence of actions using Viterbi search in the SFD-CRF. We demonstrate our approach on videos from multiple viewpoints and in the presence of background clutter.