Distributed algorithms have recently gained immense popularity. With regards to computer vision applications, distributed multi-target tracking in a camera network is a fundamental problem. The goal is for all cameras to have accurate state estimates for all targets. Distributed estimation algorithms work by exchanging information between sensors that are communication neighbors. Vision-based distributed multi-target state estimation has at least two characteristics that distinguishes it from other applications. First, cameras are directional sensors and often neighboring sensors may not be sensing the same targets, i.e., they are naive with respect to that target. Second, in the presence of clutter and multiple targets, each camera must solve a data association problem. This paper presents an information-weighted, consensus-based, distributed multi-target tracking algorithm referred to as the Multi-target Information Consensus (MTIC) algorithm that is designed to address both the naivety and the data association problems. It converges to the centralized minimum mean square error estimate. The proposed MTIC algorithm and its extensions to non-linear camera models, termed as the Extended MTIC (EMTIC), are robust to false measurements and limited resources like power, bandwidth and the real-time operational requirements. Simulation and experimental analysis are provided to support the theoretical results.

Due to their high fault-tolerance, ease of installation and scalability to large networks, distributed algorithms have recently gained immense popularity in the sensor networks community, especially in computer vision. Multi-target tracking in a camera network is one of the fundamental problems in this domain. Distributed estimation algorithms work by exchanging information between sensors that are communication neighbors. Since most cameras are directional sensors, it is often the case that neighboring sensors may not be sensing the same target. Such sensors that do not have information about a target are termed as ``naive'' with respect to that target. In this paper, we propose consensus-based distributed multi-target tracking algorithms in a camera network that are designed to address this issue of naivety. The estimation errors in tracking and data association, as well as the effect of naivety, are jointly addressed leading to the development of an information-weighted consensus algorithm, which we term as the Multi-target Information Consensus (MTIC) algorithm. The incorporation of the probabilistic data association mechanism makes the MTIC algorithm very robust to false measurements/clutter. Experimental analysis is provided to support the theoretical results.

Distributed algorithms in the sensors networks community usually require each sensor to have its own measurement. In practice, this constraint can not always be met. For example, in a camera network, all cameras might not observe a particular target as cameras are directional sensors and have a limited field-of-view (FOV). Moreover, different sensors might provide different quality measures related to different elements of the measurement vector depending on various factors as directionality, occlusion etc. This requires the designing of a new type of distributed algorithm that considers the quality and/or absence of measurements. In this paper, we present a distributed algorithm to compute the maximum likelihood estimate of the state of a target viewed by the network of cameras, taking into account the above-mentioned factors. We provide step-by-step derivation along with theoretical guarantee of optimality and convergence of the method. Experimental results are provided to show the performance of the proposed algorithm.

In this work, we consider a camera network where processing is distributed across the cameras. Our goal is to recognize actions of multiple targets consistently observed over the entire network. To obtain consistent and better results we need to properly fuse the action scores from multiple cameras. There have been multiple works on distributed tracking and distributed data association for multiple targets in a camera network. We can use the data association results and tracking confidence scores to improve the action recognition results. We propose a consensus based framework for solving this problem in an integrated manner and with a completely distributed camera network architecture. We propose a novel method for weighting the action scores based on tracking confidences and show how the cameras can reach a consensus about the action of a target using belief consensus. We show real life experiments and performance metrics with multiple cameras and targets.

Identification of motion patterns in video is an important problem because it is the first step towards analysis of complex multi-person behaviors to obtain long-term interaction models. In this paper, we will present a flow based technique to identify spatio-temporal motion patterns in a multi-object video. We use the Helmholtz decomposition of optical flow and compute singular points corresponding to component fields. We will show that the optical flow can be used to identify regions which correspond to different moving entities in the video. The singular points in these regions capture the characteristics of the field around them and can be used to identify these regions. This representation would provide us with a framework to analyze activities of individual entities in the scene as well as the global interactions between them. We demonstrate our algorithm on a dataset composed of multi-object videos recorded in a realistic environment.

Camera networks are being deployed for various applications like security and surveillance, disaster response and environmental modeling. However, there is little automated processing of the data. Moreover, most methods for multicamera analysis are centralized schemes that require the data to be present at a central server. In many applications, this is prohibitively expensive, both technically and economically. In this paper, we investigate distributed scene analysis algorithms by leveraging upon concepts of consensus that have been studied in the context of multiagent systems, but have had little applications in video analysis. Each camera estimates certain parameters based upon its own sensed data which is then shared locally with the neighboring cameras in an iterative fashion, and a final estimate is arrived at in the network using consensus algorithms. We specifically focus on two basic problems-tracking and activity recognition. For multitarget tracking in a distributed camera network, we show how the Kalman-Consensus algorithm can be adapted to take into account the directional nature of video sensors and the network topology. For the activity recognition problem, we derive a probabilistic consensus scheme that combines the similarity scores of neighboring cameras to come up with a probability for each action at the network level. Thorough experimental results are shown on real data along with a quantitative analysis.