Viewpoint Independent Action Recognition

Action recognition is a popular and important research topic in computer vision. However, it is challenging when facing viewpoint variance. So far, most researches in action recognition remain rooted in view-dependent representations. Some view invariance approaches have been proposed, but most of them suffer from some weaknesses, such as lack of abundant information for recognition, dependency on robust meaningful feature detection or point correspondence. To perform viewpoint and subject independent action recognition, this paper proposes a representation called "Envelop Shape" which is viewpoint insensitive. "Envelop Shape" is easy to acquire from silhouettes using two orthogonal cameras. It makes full use of two cameras' silhouettes to dispel influence caused by human body's vertical rotation, which is often the primary viewpoint variance. With the help of "Envelop Shape" representation and Hidden Markov Model, the inspiring results on action recognition independent of subject and viewpoint are obtained. Results indicate that "Envelop Shape" representation contains enough discriminating features for action recognition. Extension of "Envelop Shape" is also proposed to make it run under fewer restrictions of camera configurations, which increases its application value effectively.