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

Reinforcement Learning of User Preferences for a Ubiquitous Personal Assistant

Open access book: http://www.intechopen.com/books/advances-in-reinforcement-learningInternational audienceNew technologies bring a multiplicity of new possibilities for users to work with computers. Not only are spaces more and more equipped with stationary computers or notebooks, but more and more users carry mobile devices with them (smart-phones, personal digital assistants, etc.). Ubiquitous computing aims at creating smart environments where devices are dynamically linked in order to provide new services to users and new human-machine interaction possibilities. The most profound technologies are those that disappear. They weave themselves into the fabric of everyday life until they are indistinguishable from it (Weiser, 1991). This network of devices must perceive the context in order to understand and anticipate the user's needs. Devices should be able to execute actions that help the user to fulfill his goal or that simply accommodate him. Actions depend on the user's context and, in particular, on the situation within the context. The objective of this work is to construct automatically a context model by applying reinforcement learning techniques. Rewards are given by the user when expressing his degree of satisfaction towards actions proposed by the system. A default context model is used from the beginning in order to have a consistent initial behavior. This model is then adapted to each particular user in a way that maximizes the user's satisfaction towards the system's actions

Towards Unsupervised Sudden Group Movement Discovery for Video Surveillance

International audienceThis paper presents a novel and unsupervised approach for discovering "sudden" movements in video surveillance videos. The proposed approach automatically detects quick motions in a video, corresponding to any action. A set of possible actions is not required and the proposed method successfully detects potentially alarm-raising actions without training or camera calibration. Moreover, the system uses a group detection and event recognition framework to relate detected sudden movements and groups of people, and provide a semantical interpretation of the scene. We have tested our approach on a dataset of nearly 8 hours of videos recorded from two cameras in the Parisian subway for a European Project. For evaluation, we annotated 1 hour of sequences containing 50 sudden movements

Group Tracking and Behavior Recognition in Long Video Surveillance Sequences

International audienceThis paper makes use of recent advances in group tracking and behavior recognition to process large amounts of video surveillance data from an underground railway station and perform a statistical analysis. The most important advantages of our approach are the robustness to process long videos and the capacity to recognize several and different events at once. This analysis automatically brings forward data about the usage of the station and the various behaviors of groups in different hours of the day. This data would be very hard to obtain without an automatic group tracking and behavior recognition method. We present the results and interpretation of one month of processed data from a video surveillance camera in the Torino subway

Improving Person Re-identification by Viewpoint Cues

International audienceRe-identifying people in a network of cameras requires an invariant human representation. State of the art algorithms are likely to fail in real-world scenarios due to serious perspective changes. Most of existing approaches focus on invariant and discriminative features, while ignoring the body alignment issue. In this paper we propose 3 methods for improving the performance of person re-identification. We focus on eliminating perspective distortions by using 3D scene information. Perspective changes are minimized by affine transformations of cropped images containing the target (1). Further we estimate the human pose for (2) clustering data from a video stream and (3) weighting image features. The pose is estimated using 3D scene information and motion of the target. We validated our approach on a publicly available dataset with a network of 8 cameras. The results demonstrated significant increase in the re-identification performance over the state of the art

Group interaction and group tracking for video-surveillance in underground railway stations

International audienceIn this paper we propose an approach to recognize behaviors of groups of people in the subway. Violent behavior or vandalism performed by a group can be detected in order to alert subway security. The proposed system is composed of 3 main layers: the detection of people in the video, the detection and tracking of groups among the detected individuals and the detection of events and scenarios of interest based on tracked actors (groups). The main focus of this paper are the group tracking and event detection layers

Apprentissage par renforcement de modeles de contexte pour l'informatique ambiante

This thesis studies the automatic acquisition by machine learning of a context model for a user in a ubiquitous environment. In such an environment, devices can communicate and cooperate in order to create a consistent computerized space. Some devices possess perceptual capabilities. The environment uses them to detect the user's situation - his context. Other devices are able to execute actions. Our problematics consists in determining the optimal associations, for a given user, between situations and actions. Machine learning seems to be a sound approach since it results in a customized environment without requiring an explicit specification from the user. A life long learning lets the environment adapt itself continuously to world changes and user preferences changes. Reinforcement learning can be a solution to this problem, as long as it is adapted to some particular constraints due to our application setting.Cette thèse étudie l'acquisition automatique par apprentissage d'un modèle de contexte pour un utilisateur dans un environnement ubiquitaire. Dans un tel environnement, les dispositifs peuvent communiquer et coopérer afin de former un espace informatique cohérent. Certains appareils ont des capacités de perception, utilisées par l'environnement pour détecter la situation - le contexte - de l'utilisateur. D'autres appareils sont capables d'exécuter des actions. La problématique que nous nous sommes posée est de déterminer les associations optimales pour un utilisateur donné entre les situations et les actions. L'apprentissage apparaît comme une bonne approche car il permet de personnaliser l'environnement sans spécification explicite de la part de l'usager. Un apprentissage à vie permet, par ailleurs, de toujours s'adapter aux modifications du monde et des préférences utilisateur. L'apprentissage par renforcement est un paradigme d'apprentissage qui peut être une solution à notre problème, à condition de l'adapter aux contraintes liées à notre cadre d'application

Apprentissage par renforcement de modeles de contexte pour l'informatique ambiante

This thesis studies the automatic acquisition by machine learning of a context model for a user in a ubiquitous environment. In such an environment, devices can communicate and cooperate in order to create a consistent computerized space. Some devices possess perceptual capabilities. The environment uses them to detect the user's situation - his context. Other devices are able to execute actions. Our problematics consists in determining the optimal associations, for a given user, between situations and actions. Machine learning seems to be a sound approach since it results in a customized environment without requiring an explicit specification from the user. A life long learning lets the environment adapt itself continuously to world changes and user preferences changes. Reinforcement learning can be a solution to this problem, as long as it is adapted to some particular constraints due to our application setting.Cette thèse étudie l'acquisition automatique par apprentissage d'un modèle de contexte pour un utilisateur dans un environnement ubiquitaire. Dans un tel environnement, les dispositifs peuvent communiquer et coopérer afin de former un espace informatique cohérent. Certains appareils ont des capacités de perception, utilisées par l'environnement pour détecter la situation - le contexte - de l'utilisateur. D'autres appareils sont capables d'exécuter des actions. La problématique que nous nous sommes posée est de déterminer les associations optimales pour un utilisateur donné entre les situations et les actions. L'apprentissage apparaît comme une bonne approche car il permet de personnaliser l'environnement sans spécification explicite de la part de l'usager. Un apprentissage à vie permet, par ailleurs, de toujours s'adapter aux modifications du monde et des préférences utilisateur. L'apprentissage par renforcement est un paradigme d'apprentissage qui peut être une solution à notre problème, à condition de l'adapter aux contraintes liées à notre cadre d'application

Learning User Preferences in Ubiquitous Systems: A User Study and a Reinforcement Learning Approach

Abstract. Our study concerns a virtual assistant, proposing services to the user based on its current perceived activity and situation (ambient intelligence). Instead of asking the user to define his preferences, we acquire them automatically using a reinforcement learning approach. Experiments showed that our system succeeded the learning of user preferences. In order to validate the relevance and usability of such a system, we have first conducted a user study. 26 non-expert subjects were interviewed using a model of the final system. This paper presents the methodology of applying reinforcement learning to a real-world problem with experimental results and the conclusions of the user study