A multi-resolution outdoor dual camera system for robust video-event metadata extraction

This paper describes a cooperative distributed system for outdoor surveillance based on fixed and mobile cameras. In order to continuously monitor the entire scene, a fixed unidirectional sensor has been used, mounted on the roof of a building in front of the guarded area. To obtain higher resolution images of a particular region in the scene, an active pan-tilt-zoom camera has been used. The low resolution images are used to detect and locate moving objects in a scene. The estimated object position is used in order to evaluate pan-tilt movements that are necessary in order to focus the attention of the mobile-head camera on the considered object at a higher zoom level. The system is able to provide automatic change detection at multiple zoom levels. A video shot with a small zoom factor is used to monitor the entire scene from a fixed camera, while a medium and high zoom factor are used to improve interpretation of the scene. The use of a mobile camera allows one to exceed the limitations of the bounded field of view of the sensor imposed by a fixed camera. In this case it is not possible to provide a priori knowledge about the background of the scene. The proposed method for solving the non-fixed background problem for mobile cameras involves realization of a multilevel structure obtained by the acquisition of several images. The panoramic image of the whole scene is generated using a mosaicing technique. Both sensors are used to detect and estimate the precise location of a given object at different zoom levels in order to obtain a better position estimation.