Action Recognition, Temporal Localization and Detection in Trimmed and Untrimmed Video

Automatic understanding of videos is one of the most active areas of computer vision research. It has applications in video surveillance, human computer interaction, video sports analysis, virtual and augmented reality, video retrieval etc. In this dissertation, we address four important tasks in video understanding, namely action recognition, temporal action localization, spatial-temporal action detection and video object/action segmentation. This dissertation makes contributions to above tasks by proposing. First, for video action recognition, we propose a category level feature learning method. Our proposed method automatically identifies such pairs of categories using a criterion of mutual pairwise proximity in the (kernelized) feature space, and a category-level similarity matrix where each entry corresponds to the one-vs-one SVM margin for pairs of categories. Second, for temporal action localization, we propose to exploit the temporal structure of actions by modeling an action as a sequence of sub-actions and present a computationally efficient approach. Third, we propose 3D Tube Convolutional Neural Network (TCNN) based pipeline for action detection. The proposed architecture is a unified deep network that is able to recognize and localize action based on 3D convolution features. It generalizes the popular faster R-CNN framework from images to videos. Last, an end-to-end encoder-decoder based 3D convolutional neural network pipeline is proposed, which is able to segment out the foreground objects from the background. Moreover, the action label can be obtained as well by passing the foreground object into an action classifier. Extensive experiments on several video datasets demonstrate the superior performance of the proposed approach for video understanding compared to the state-of-the-art

Going Deeper into Action Recognition: A Survey

Understanding human actions in visual data is tied to advances in complementary research areas including object recognition, human dynamics, domain adaptation and semantic segmentation. Over the last decade, human action analysis evolved from earlier schemes that are often limited to controlled environments to nowadays advanced solutions that can learn from millions of videos and apply to almost all daily activities. Given the broad range of applications from video surveillance to human-computer interaction, scientific milestones in action recognition are achieved more rapidly, eventually leading to the demise of what used to be good in a short time. This motivated us to provide a comprehensive review of the notable steps taken towards recognizing human actions. To this end, we start our discussion with the pioneering methods that use handcrafted representations, and then, navigate into the realm of deep learning based approaches. We aim to remain objective throughout this survey, touching upon encouraging improvements as well as inevitable fallbacks, in the hope of raising fresh questions and motivating new research directions for the reader

Improving a 3-D Convolutional Neural Network Model Reinvented from VGG16 with Batch Normalization

It is challenging to build and train a Convolutional Neural Network model that can achieve a high accuracy rate for the first time. There are many variables to consider such as initial parameters, learning rate, and batch size. Unsuccessfully training a model is one of the most inevitable problems. In some cases, the model struggles to find a lower Loss Function value which results in a poor performance. Batch Normalization is considered as a remedy to overcome this problem. In this paper, two models reinvented from VGG16 are created with and without using Batch Normalization to evaluate their model performance. It is clear that the model using Batch Normalization provides a better result in terms of Loss Function value and model accuracy, which also achieves a very high accuracy rate. It also reaches the saturation point of the highest model accuracy faster than the model without Batch Normalization. This paper also finds that the accuracy of 3D Convolutional Neural Network model reinvented from VGG16 with Batch Normalization is at 91.2% which can beat many benchmarking results on UCF101 such as IDT [5], Two-Stream [10], and Dynamic Image Networks IDT [4]. The technique introduced in this paper shows a fast, reliable and accurate estimation of human activity type and could be used in smart environments