Théorie de l’évidence pour suivi de visage

Le suivi de visage par caméra vidéo est abordé ici sous l’angle de la fusion évidentielle. La méthode proposée repose sur un apprentissage sommaire basé sur une initialisation supervisée. Le formalisme du modèle de croyances transférables est utilisé pour pallier l’incomplétude du modèle a priori de visage due au manque d’exhaustivité de la base d’apprentissage. L’algorithme se décompose en deux étapes. La phase de détection de visage synthétise un modèle évidentiel où les attributs du détecteur de Viola et Jones sont convertis en fonctions de croyance, et fusionnés avec des fonctions de masse couleur modélisant un détecteur de teinte chair, opérant dans un espace chromatique original obtenu par transformation logarithmique. Pour fusionner les sources couleur dépendantes, nous proposons un opérateur de compromis inspiré de la règle prudente de Denœux. Pour la phase de suivi, les probabilités pignistiques issues du modèle de visage garantissent la compatibilité entre les cadres crédibiliste et probabiliste. Elles alimentent un filtre particulaire classique qui permet le suivi du visage en temps réel. Nous analysons l’influence des paramètres du modèle évidentiel sur la qualité du suivi.This paper deals with real time face detection and tracking by a video camera. The method is based on a simple and fast initializing stage for learning. The transferable belief model is used to deal with the prior model incompleteness due to the lack of exhaustiveness of the learning stage. The algorithm works in two steps. The detection phase synthesizes an evidential face model by merging basic beliefs elaborated from the Viola and Jones face detector and from colour mass functions. These functions are computed from information sources in a logarithmic colour space. To deal with the colour information dependence in the fusion process, we propose a compromise operator close to the Denœux cautious rule. As regards the tracking phase, the pignistic probabilities from the face model guarantee the compatibility between the believes and the probability formalism. They are the inputs of a particle filter which ensures face tracking at video rate. The optimal parameter tuning of the evidential model is discussed

Robust face tracking using colour Dempster-Shafer fusion and particle filter

International audienceThis paper describes a real time face detection and tracking system. The method consists in modelling the skin face by a pixel fusion process of three colour sources within the framework of the Demster-Shafer theory. The algorithm is composed of two phases. In a simple and fast initialising stage, the user selects successively on an image, a shadowy, an overexposed and a zone of mean intensity of the face. Then the fusion process models the face skin colour. Next, on the video sequence, a tracking phase uses the key idea that the face exterior edges are well approximated as an ellipse including the skin colour blob resulting from the fusion process. As ellipse detection gets easily disturbed in cluttered environnements by edges caused by non-face objects, a simple and fast efficient least squares method for ellipse fitting is used. The ellipse parameters (center, minor axis, major axis, orientation) are taken into account by a stochastic algorithm using a particle filter in order to realise a robust face tracking in position, size and pose. The originality of the method consists in modelling the face skin by a pixel fusion process of three independant cognitive colour sources. Moreover, mass sets are determined from a priori models taking into account contextual variables specific to the face under study. Hence, the face particularity which is to present shadowy (neck) and overexposed (nose, front) zones is considered, sosensitivity to lighting conditions decreases. Results of face skin modelling, fusion, ellipse fitting and tracking are illustrated and discussed in this paper. The limits of the method and future works are also commented in conclusion

A Dempster-Shafer Method for Multi-Sensor Fusion

The Dempster-Shafer Theory, a generalization of the Bayesian theory, is based on the idea of belief and as such can handle ignorance. When all of the required information is available, many data fusion methods provide a solid approach. Yet, most do not have a good way of dealing with ignorance. In the absence of information, these methods must then make assumptions about the sensor data. However, the real data may not fit well within the assumed model. Consequently, the results are often unsatisfactory and inconsistent. The Dempster-Shafer Theory is not hindered by incomplete models or by the lack of prior information. Evidence is assigned based solely on what is known, and nothing is assumed. Hence, it can provide a fast and accurate means for multi-sensor fusion with ignorance. In this research, we apply the Dempster-Shafer Theory in target tracking and in gait analysis. We also discuss the Dempster-Shafer framework for fusing data from a Global Positioning System (GPS) and an Inertial Measurement Unit (IMU) sensor unit for precise local navigation. Within this application, we present solutions where GPS outages occur