Large-scale Continuous Gesture Recognition Using Convolutional Neural Networks

This paper addresses the problem of continuous gesture recognition from sequences of depth maps using convolutional neutral networks (ConvNets). The proposed method first segments individual gestures from a depth sequence based on quantity of movement (QOM). For each segmented gesture, an Improved Depth Motion Map (IDMM), which converts the depth sequence into one image, is constructed and fed to a ConvNet for recognition. The IDMM effectively encodes both spatial and temporal information and allows the fine-tuning with existing ConvNet models for classification without introducing millions of parameters to learn. The proposed method is evaluated on the Large-scale Continuous Gesture Recognition of the ChaLearn Looking at People (LAP) challenge 2016. It achieved the performance of 0.2655 (Mean Jaccard Index) and ranked $3^{rd}$ place in this challenge

Recurrent Attention Models for Depth-Based Person Identification

We present an attention-based model that reasons on human body shape and motion dynamics to identify individuals in the absence of RGB information, hence in the dark. Our approach leverages unique 4D spatio-temporal signatures to address the identification problem across days. Formulated as a reinforcement learning task, our model is based on a combination of convolutional and recurrent neural networks with the goal of identifying small, discriminative regions indicative of human identity. We demonstrate that our model produces state-of-the-art results on several published datasets given only depth images. We further study the robustness of our model towards viewpoint, appearance, and volumetric changes. Finally, we share insights gleaned from interpretable 2D, 3D, and 4D visualizations of our model's spatio-temporal attention.Comment: Computer Vision and Pattern Recognition (CVPR) 201

Simple and Complex Human Action Recognition in Constrained and Unconstrained Videos

Human action recognition plays a crucial role in visual learning applications such as video understanding and surveillance, video retrieval, human-computer interactions, and autonomous driving systems. A variety of methodologies have been proposed for human action recognition via developing of low-level features along with the bag-of-visual-word models. However, much less research has been performed on the compound of pre-processing, encoding and classification stages. This dissertation focuses on enhancing the action recognition performances via ensemble learning, hybrid classifier, hierarchical feature representation, and key action perception methodologies. Action variation is one of the crucial challenges in video analysis and action recognition. We address this problem by proposing the hybrid classifier (HC) to discriminate actions which contain similar forms of motion features such as walking, running, and jogging. Aside from that, we show and proof that the fusion of various appearance-based and motion features can boost the simple and complex action recognition performance. The next part of the dissertation introduces pooled-feature representation (PFR) which is derived from a double phase encoding framework (DPE). Considering that a given unconstrained video is composed of a sequence of simple frames, the first phase of DPE generates temporal sub-volumes from the video and represents them individually by employing the proposed improved rank pooling (IRP) method. The second phase constructs the pool of features by fusing the represented vectors from the first phase. The pool is compressed and then encoded to provide video-parts vector (VPV). The DPE framework allows distilling the video representation and hierarchically extracting new information. Compared with recent video encoding approaches, VPV can preserve the higher-level information through standard encoding of low-level features in two phases. Furthermore, the encoded vectors from both phases of DPE are fused along with a compression stage to develop PFR

Multimodal Prototype-Enhanced Network for Few-Shot Action Recognition

Current methods for few-shot action recognition mainly fall into the metric learning framework following ProtoNet. However, they either ignore the effect of representative prototypes or fail to enhance the prototypes with multimodal information adequately. In this work, we propose a novel Multimodal Prototype-Enhanced Network (MORN) to use the semantic information of label texts as multimodal information to enhance prototypes, including two modality flows. A CLIP visual encoder is introduced in the visual flow, and visual prototypes are computed by the Temporal-Relational CrossTransformer (TRX) module. A frozen CLIP text encoder is introduced in the text flow, and a semantic-enhanced module is used to enhance text features. After inflating, text prototypes are obtained. The final multimodal prototypes are then computed by a multimodal prototype-enhanced module. Besides, there exist no evaluation metrics to evaluate the quality of prototypes. To the best of our knowledge, we are the first to propose a prototype evaluation metric called Prototype Similarity Difference (PRIDE), which is used to evaluate the performance of prototypes in discriminating different categories. We conduct extensive experiments on four popular datasets. MORN achieves state-of-the-art results on HMDB51, UCF101, Kinetics and SSv2. MORN also performs well on PRIDE, and we explore the correlation between PRIDE and accuracy