Figure 5 presents six frames from a 2 minute sequence

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Unformatted text preview: on from the moment she enters the subway platform till she gets on the train ( 3600 frames). The tracking performance is remarkable, taking into account the low quality of the processed sequence, due to the compression artifacts. A thorough evaluation of the tracker, however, is subject to our current work. The minimum value of the distance (18) for each frame is shown in Figure 6. The compression noise determined the distance to increase from 0 (perfect match) to a stationary value of about 0:3. Signi cant deviations from this value correspond to occlusions generated by other persons or rotations in depth of the target. The large distance increase at the end signals the complete occlusion of the target. Figure 4: Subway1 sequence: The frames 500, 529, 600, 633, and 686 are shown (left-right, top-down). histogram of a face model onto the incoming frame. However, the direct projection of the model histogram onto the new frame can introduce a large bias in the estimated location of the target, and the resulting measure is scale variant. Gradient based region tracking has been formulated in 2] by minimizing the energy of the deformable region, but no real-time claims were made. 6 Discussion By exploiting the spatial gradient of the statistical measure (18) the new method achieves real-time tracking performance, while e ectively rejecting background clutter and partial occlusions. Note that the same technique can be employed to derive the measurement vector for optimal prediction schemes such as the (Extended) Kalman lter 1, p.56, 106], or multiple hypothesis tracking approaches 5, 9, 17, 18]. In return, the prediction can determine the priors (de ning the presence of the target in a given neighborhood) assumed equal in this paper. This connection is however beyond the scope of this paper. A patent application has been led covering the tracking algorithm together with the Kalman extension and various applications 29]. We nally observe that the idea of centroid computation is also employed in 22]. The mea...
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