Natural Language Description of Images and Videos

Understanding visual media, i.e. images and videos, has been a cornerstone topic in computer vision research for a long time. Recently, a new task within the purview of this research area, that of automatically captioning images and videos, has garnered wide-spread interest. The task involves generating a short natural language description of an image or a video. This thesis studies the automatic visual captioning problem in its entirety. A baseline visual captioning pipeline is examined, including its two constituent blocks, namely visual feature extraction and language modeling. We then discuss the challenges involved and the methods available to evaluate a visual captioning system. Building on this baseline model, several enhancements are proposed to improve the performance of both the visual feature extraction and the language modeling. Deep convolutional neural network based image features used in the baseline model are augmented with explicit object and scene detection features. In the case of videos, a combination of action recognition and static frame-level features are used. The long-short term memory network based language model used in the baseline is extended by introduction of an additional input channel and residual connections. Finally, an efficient ensembling technique based on a caption evaluator network is presented. Results from extensive experiments conducted to evaluate each of the above mentioned enhancements are reported. The image and video captioning architectures proposed in this thesis achieve state-of-the-art performance on the corresponding tasks. To support these claims, results from two video captioning challenges organized over the last year are reported, both of which were won by the models presented in the thesis. We also quantitatively analyze the automatic captions generated and identify several shortcomings of the current system. After having identified the deficiencies, we briefly look at a few interesting problems which could take the automatic visual captioning research forward

Generating Natural Questions About an Image

There has been an explosion of work in the vision & language community during the past few years from image captioning to video transcription, and answering questions about images. These tasks have focused on literal descriptions of the image. To move beyond the literal, we choose to explore how questions about an image are often directed at commonsense inference and the abstract events evoked by objects in the image. In this paper, we introduce the novel task of Visual Question Generation (VQG), where the system is tasked with asking a natural and engaging question when shown an image. We provide three datasets which cover a variety of images from object-centric to event-centric, with considerably more abstract training data than provided to state-of-the-art captioning systems thus far. We train and test several generative and retrieval models to tackle the task of VQG. Evaluation results show that while such models ask reasonable questions for a variety of images, there is still a wide gap with human performance which motivates further work on connecting images with commonsense knowledge and pragmatics. Our proposed task offers a new challenge to the community which we hope furthers interest in exploring deeper connections between vision & language.Comment: Proceedings of the 54th Annual Meeting of the Association for Computational Linguistic

Cognitive visual tracking and camera control

Cognitive visual tracking is the process of observing and understanding the behaviour of a moving person. This paper presents an efficient solution to extract, in real-time, high-level information from an observed scene, and generate the most appropriate commands for a set of pan-tilt-zoom (PTZ) cameras in a surveillance scenario. Such a high-level feedback control loop, which is the main novelty of our work, will serve to reduce uncertainties in the observed scene and to maximize the amount of information extracted from it. It is implemented with a distributed camera system using SQL tables as virtual communication channels, and Situation Graph Trees for knowledge representation, inference and high-level camera control. A set of experiments in a surveillance scenario show the effectiveness of our approach and its potential for real applications of cognitive vision

Frame- and Segment-Level Features and Candidate Pool Evaluation for Video Caption Generation

We present our submission to the Microsoft Video to Language Challenge of generating short captions describing videos in the challenge dataset. Our model is based on the encoder--decoder pipeline, popular in image and video captioning systems. We propose to utilize two different kinds of video features, one to capture the video content in terms of objects and attributes, and the other to capture the motion and action information. Using these diverse features we train models specializing in two separate input sub-domains. We then train an evaluator model which is used to pick the best caption from the pool of candidates generated by these domain expert models. We argue that this approach is better suited for the current video captioning task, compared to using a single model, due to the diversity in the dataset. Efficacy of our method is proven by the fact that it was rated best in MSR Video to Language Challenge, as per human evaluation. Additionally, we were ranked second in the automatic evaluation metrics based table

Describing Videos by Exploiting Temporal Structure

Recent progress in using recurrent neural networks (RNNs) for image description has motivated the exploration of their application for video description. However, while images are static, working with videos requires modeling their dynamic temporal structure and then properly integrating that information into a natural language description. In this context, we propose an approach that successfully takes into account both the local and global temporal structure of videos to produce descriptions. First, our approach incorporates a spatial temporal 3-D convolutional neural network (3-D CNN) representation of the short temporal dynamics. The 3-D CNN representation is trained on video action recognition tasks, so as to produce a representation that is tuned to human motion and behavior. Second we propose a temporal attention mechanism that allows to go beyond local temporal modeling and learns to automatically select the most relevant temporal segments given the text-generating RNN. Our approach exceeds the current state-of-art for both BLEU and METEOR metrics on the Youtube2Text dataset. We also present results on a new, larger and more challenging dataset of paired video and natural language descriptions.Comment: Accepted to ICCV15. This version comes with code release and supplementary materia

Generating a 3D Simulation of a Car Accident from a Written Description in Natural Language: the CarSim System

This paper describes a prototype system to visualize and animate 3D scenes from car accident reports, written in French. The problem of generating such a 3D simulation can be divided into two subtasks: the linguistic analysis and the virtual scene generation. As a means of communication between these two modules, we first designed a template formalism to represent a written accident report. The CarSim system first processes written reports, gathers relevant information, and converts it into a formal description. Then, it creates the corresponding 3D scene and animates the vehicles.Comment: 8 pages, ACL 2001, Workshop on Temporal and Spatial Information Processin