Time to contact from active tracking of motion boundaries

This paper addresses the problem of recovering time-to-contact by actively tracking motion boundaries. Unlike previous approaches which use image features, we use the camera's own motion to both detect and track object boundaries. First we develop a framework in which the boundaries of objects are automatically detected using the motion parallax caused by the motion of an active camera. We use a correlation-based method to locate motion boundaries and our work has focused on detecting the motion boundaries early and robustly. A confidence field, which expresses the likelihood that a point lies on a motion boundary, is constructed from the shape of the correlation surface. Spatial coherence of object boundaries is modeled with dynamic contours which are automatically initialized using an attentional mechanism. Then, as the camera moves, the shapes of the dynamic contours are held fixed and they are tracked under an assumption of affine deformation. The affine parameters are recovered from the active tracking over time and are used to compute time-to-contact. We illustrate the behavior of this active approach with experiments on both synthetic and real image sequences.

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