Action Chart: A Representation for Efficient Recognition of Complex Activities

In this paper we propose an efficient method for the recognition of long and complex action streams. First, we design a new motion feature flow descriptor by composing low-level local features. Then a new data embedding method is developed in order to represent the motion flow as an one-dimensional sequence, whilst preserving useful motion information for recognition. Finally attentional motion spots (AMSs) are defined to automatically detect meaningful motion changes from the embedded one-dimensional sequence. An unsupervised learning strategy based on expectation maximization and a weighted Gaussian mixture model is then applied to the AMSs for each action class, resulting in an action representation which we refer to as Action Chart. The Action Chart is then used efficiently for recognizing each action class. Through comparison with the state-of-the-art methods, experimental results show that the Action Chart gives promising recognition performance with low computational load and can be used for abstracting long video sequences.