Classification of Human Actions Using 3-D Convolutional Neural Networks: A Hierarchical Approach

In this paper, we present a hierarchical approach for human action classification using 3-D Convolutional neural networks (3-D CNN). In general, human actions refer to positioning and movement of hands and legs and hence can be classified based on those performed by hands or by legs or, in some cases, both. This acts as the intuition for our work on hierarchical classification. In this work, we consider the actions as tasks performed by hand or leg movements. Therefore, instead of using a single 3-D CNN for classification of given actions, we use multiple networks to perform the classification hierarchically, that is, we first perform binary classification to separate the hand and leg actions and then use two separate networks for hand and leg actions to perform classification among target action categories. For example, in case of KTH dataset, we train three networks to classify six different actions, comprising of three actions each for hands and legs. The novelty of our approach lies in performing the separation of hand and leg actions first, thus making the subsequent classifiers to accept the features corresponding to either hands or legs only. This leads to better classification accuracy. Also, the use of 3-D CNN enables automatic extraction of features in spatial as well as temporal domain, avoiding the need for hand crafted features. This makes it one of the better approaches when it comes to video classification. We use the KTH, Weizmann and UCF-sports datasets to evaluate our method and comparison with the state of the art methods shows that our approach outperforms most of them.