Temporal Hierarchical Dictionary with HMM for Fast Gesture Recognition

In this paper, we propose a novel temporal hierarchical dictionary with hidden Markov model (HMM) for gesture recognition task. Dictionaries with spatio-temporal elements have been commonly used for gesture recognition. However, the existing spatio-temporal dictionary based methods need the whole pre-segmented gestures for inference, thus are hard to deal with non-stationary sequences. The proposed method combines HMM with Deep Belief Networks (DBN) to tackle both gesture segmentation and recognition by the inference at the frame level. Besides, we investigate the redundancy in dictionaries and introduce the relative entropy to measure the information richness of a dictionary. Furthermore, when inferring an element, a temporal hierarchy-flat dictionary will be searched entirely every time in which the temporal structure of gestures isn't utilized sufficiently. The proposed temporal hierarchical dictionary is organized in HMM states and can limit the search range to distinct states. Our framework includes three key novel properties: (1) a temporal hierarchical structure with HMM, which makes both the HMM transition and Viterbi decoding more efficient; (2) a relative entropy model to compress the dictionary with less redundancy; (3) an unsupervised hierarchical clustering algorithm to build a hierarchical dictionary automatically. Our method is evaluated on two gesture datasets and consistently achieves state-of-the-art performance. The results indicate that the dictionary redundancy has a significant impact on the performance which can be tackled by a temporal hierarchy and an entropy model.