A generic framework for video understanding applied to group behavior recognition

This paper presents an approach to detect and track groups of people in video-surveillance applications, and to automatically recognize their behavior. This method keeps track of individuals moving together by maintaining a spacial and temporal group coherence. First, people are individually detected and tracked. Second, their trajectories are analyzed over a temporal window and clustered using the Mean-Shift algorithm. A coherence value describes how well a set of people can be described as a group. Furthermore, we propose a formal event description language. The group events recognition approach is successfully validated on 4 camera views from 3 datasets: an airport, a subway, a shopping center corridor and an entrance hall.Comment: (20/03/2012

Automatic Parameter Adaptation for Multi-object Tracking

Object tracking quality usually depends on video context (e.g. object occlusion level, object density). In order to decrease this dependency, this paper presents a learning approach to adapt the tracker parameters to the context variations. In an offline phase, satisfactory tracking parameters are learned for video context clusters. In the online control phase, once a context change is detected, the tracking parameters are tuned using the learned values. The experimental results show that the proposed approach outperforms the recent trackers in state of the art. This paper brings two contributions: (1) a classification method of video sequences to learn offline tracking parameters, (2) a new method to tune online tracking parameters using tracking context.Comment: International Conference on Computer Vision Systems (ICVS) (2013

Online Tracking Parameter Adaptation based on Evaluation

Parameter tuning is a common issue for many tracking algorithms. In order to solve this problem, this paper proposes an online parameter tuning to adapt a tracking algorithm to various scene contexts. In an offline training phase, this approach learns how to tune the tracker parameters to cope with different contexts. In the online control phase, once the tracking quality is evaluated as not good enough, the proposed approach computes the current context and tunes the tracking parameters using the learned values. The experimental results show that the proposed approach improves the performance of the tracking algorithm and outperforms recent state of the art trackers. This paper brings two contributions: (1) an online tracking evaluation, and (2) a method to adapt online tracking parameters to scene contexts.Comment: IEEE International Conference on Advanced Video and Signal-based Surveillance (2013

An Unsupervised Framework for Online Spatiotemporal Detection of Activities of Daily Living by Hierarchical Activity Models

International audienceAutomatic detection and analysis of human activities captured by various sensors (e.g. 1 sequence of images captured by RGB camera) play an essential role in various research fields in order 2 to understand the semantic content of a captured scene. The main focus of the earlier studies has 3 been widely on supervised classification problem, where a label is assigned for a given short clip. 4 Nevertheless, in real-world scenarios, such as in Activities of Daily Living (ADL), the challenge is 5 to automatically browse long-term (days and weeks) stream of videos to identify segments with 6 semantics corresponding to the model activities and their temporal boundaries. This paper proposes 7 an unsupervised solution to address this problem by generating hierarchical models that combine 8 global trajectory information with local dynamics of the human body. Global information helps in 9 modeling the spatiotemporal evolution of long-term activities and hence, their spatial and temporal 10 localization. Moreover, the local dynamic information incorporates complex local motion patterns of 11 daily activities into the models. Our proposed method is evaluated using realistic datasets captured 12 from observation rooms in hospitals and nursing homes. The experimental data on a variety of 13 monitoring scenarios in hospital settings reveals how this framework can be exploited to provide 14 timely diagnose and medical interventions for cognitive disorders such as Alzheimer's disease. The 15 obtained results show that our framework is a promising attempt capable of generating activity 16 models without any supervision. 1

A multi-feature tracking algorithm enabling adaptation to context variations

We propose in this paper a tracking algorithm which is able to adapt itself to different scene contexts. A feature pool is used to compute the matching score between two detected objects. This feature pool includes 2D, 3D displacement distances, 2D sizes, color histogram, histogram of oriented gradient (HOG), color covariance and dominant color. An offline learning process is proposed to search for useful features and to estimate their weights for each context. In the online tracking process, a temporal window is defined to establish the links between the detected objects. This enables to find the object trajectories even if the objects are misdetected in some frames. A trajectory filter is proposed to remove noisy trajectories. Experimentation on different contexts is shown. The proposed tracker has been tested in videos belonging to three public datasets and to the Caretaker European project. The experimental results prove the effect of the proposed feature weight learning, and the robustness of the proposed tracker compared to some methods in the state of the art. The contributions of our approach over the state of the art trackers are: (i) a robust tracking algorithm based on a feature pool, (ii) a supervised learning scheme to learn feature weights for each context, (iii) a new method to quantify the reliability of HOG descriptor, (iv) a combination of color covariance and dominant color features with spatial pyramid distance to manage the case of object occlusion.Comment: The International Conference on Imaging for Crime Detection and Prevention (ICDP) (2011

Gesture Recognition by Learning Local Motion Signatures

International audienceThis paper overviews a new gesture recognition framework based on learning local motion signatures (LMSs) introduced by [5]. After the generation of these LMSs computed on one individual by tracking Histograms of Oriented Gradient (HOG) [2] descriptor, we learn a codebook of video-words (i.e. clusters of LMSs) using k-means algorithm on a learning gesture video database. Then the videowords are compacted to a codebook of code-words by the Maximization of Mutual Information (MMI) algorithm. At the final step, we compare the LMSs generated for a new gesture w.r.t. the learned codebook via the k-nearest neighbors (k-NN) algorithm and a novel voting strategy. Our main contribution is the handling of the N to N mapping between code-words and gesture labels with the proposed voting strategy. Experiments have been carried out on two public gesture databases: KTH [16] and IXMAS [19]. Results show that the proposed method outperforms recent state-of-the-art methods

Global tracker: An online evaluation framework to improve tracking quality

International audienceEvaluating the quality of tracking outputs is an important task in video analysis. This paper presents a new framework for estimating both detection and tracking quality during runtime. If anomalies are detected in the tracking output results, they are categorized as natural phenomena or real errors using contextual information. As this framework should be generic and work on any kind of system (single camera, camera network), a re-acquisition step using a constrained clustering algorithm is also performed in order to keep track of the object even if it leaves the scene and comes back or appears on another camera. The framework is evaluated on two datasets using different kinds of tracking algorithms

Body parts detection for people tracking using trees of Histogram of Oriented Gradient descriptors

International audienceVision algorithms face many challenging issues when it comes to analyze human activities in video surveillance applications. For instance, occlusions makes the detection and tracking of people a hard task to perform. Hence advanced and adapted solutions are required to analyze the content of video sequences. We here present a people detection algorithm based on a hierarchical tree of Histogram of Oriented Gradients referred to as HOG. The detection is coupled with independently trained body part detectors to enhance the detection performance and to reach state of the art performances. We adopt a person tracking scheme which calculates HOG dissimilarities between detected persons throughout a sequence. The algorithms are tested in videos with challenging situations such as occlusions. False alarms are further reduced by using 2D and 3D information of moving objects segmented from a background reference frame

Multi-camera Tracklet association and fusion using ensemble of visual andgeometric cues

International audienceData association and fusion is pivot for object trackingin multi-camera network. We present a novel frameworkfor solving online multi-object tracking in partially overlappingmulti-camera network by modelling tracklet associationas combinatorial optimization problem hypothesizedon ensemble of cues such as appearance, motion and geometryinformation. Our method learns discriminant weightas a measure of consistency and discriminancy of featurepatterns to make ensemble feature selection and combinationbetween local and global tracking information. Ourapproach contributes uniquely in the way tracklet selection,association and fusion is done. Once multi-view correspondencesare established using planar homography, DynamicTime Warping algorithm is used to make tracklet selectionfor which similarity has to be calculated i.e overlappingtracklets and subtracklets. Then trajectory similarities arecomputed for these selective tracklets and subtracklets usingensemble of appearance and motion cues weighted byonline learnt discriminative function. Later on, we tacklethe association problem by building a k-partite graph andassociation rules to match all the pair-wise trackets. Finally,from outcome of hungarian algorithm, the associatedtrajectories are later fused. Fusion is done based on calculatedindividual tracklet reliability criteria. Experimentalresults demonstrate our system achieve performance thatsignificantly improve the state of the art on PETS 2009

Optimized Cascade of Classifiers for People Detection Using Covariance Features

International audiencePeople detection on static images and video sequences is a critical task in many computer vision applications, like image retrieval and video surveillance. It is also one of most challenging task due to the large number of possible situations, including variations in people appearance and poses. The proposed approach optimizes an existing approach based on classification on Riemannian manifolds using covariance matrices in a boosting scheme, making training and detection faster while maintaining equivalent performances. This optimisation is achieved by clustering negative samples before training, providing a smaller number of cascade levels and less weak classifiers in most levels in comparison with the original approach. Our work was evaluated and validated on INRIA Person dataset