View-invariant action recognition using fundamental ratios

A moving plane observed by a fixed camera induces a fundamental matrix F across multiple frames, where the ratios among the elements in the upper left 2times2 submatrix are herein referred to as the Fundamental Ratios. We show that fundamental ratios are invariant to camera parameters, and hence can be used to identify similar plane motions from varying viewpoints. For action recognition, we decompose a body posture into a set of point triplets (planes). The similarity between two actions is then determined by the motion of point triplets and hence by their associated fundamental ratios, providing thus view-invariant recognition of actions. Results evaluated over 255 semi-synthetic video data with 100 independent trials at a wide range of noise levels, and also on 56 real videos of 8 different classes of actions, confirm that our method can recognize actions under substantial amount of noise, even when they have dynamic timeline maps, and the viewpoints and camera parameters are unknown and totally different.