Real-time object tracking based on optical flow and active rays

A real-time system for tracking multiple quasi-rigid objects is presented. To enable the tracking of objects having similar gray-level intensity during contacts, we use dynamic information extracted by computing sparse optical flow along the object contours. Optical flow vectors are used for updating the positions of the tracked contours in a sequence of image frames. The local properties of optical flow enable the system to track the objects during and after contact, when parts of object contours become hidden. The missing dynamic information is reconstructed by using a model of constant optical flow along an object contour. To deal with the contours of changing-shape, a contour-correcting procedure based on an active contour model is added. The robustness of the tracking algorithm is improved by adding a supervision module, which detects tracking failures and reinitializes the lost contours. The system has been tested on real sequences with laboratory animals during pharmacological experiments and has been shown to be sufficiently robust and efficient.