A Two Stage Real-Time Object Tracking System

Abstract

Active contour models (snakes) can be used for contour description and extraction, as well as for object tracking in image sequences. Two unsolved problems for real time object tracking are the problem of an automatic initialization of the snake on the object and the proof of robustness of this object tracking method.

In this paper we describe a two stage real time object tracking system. In the first stage, the moving object is detected and the active contour is initialized. In the second stage, the object is tracked by active contour models. The parameters of the camera and the frame grabbing device are continuously updated in such a way, that the moving object will always be kept in the center of the image. We show how features can be extracted out of the snake tracking the object which are used for detection of errors in the tracking stage. In this case the system switches back to the first stage for object localization.

We illustrate through examples that a robust tracking over long image sequences in real time is possible within this two stage system. For experimental evaluation of the tracking result, we present a formal error measure. Using this measure, the moving object is correctly in the center of the image in up to 95 percent of all images.