An iir lter is used to derive the new radius based on

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Unformatted text preview: rrent measurements and old radius. 5 Experiments The proposed method has been applied to the task of tracking a football player marked by a hand-drawn ellipsoidal region ( rst image of Figure 1). The sequence has 154 frames of 352 240 pixels each and the initial normalization constants (determined from the size of the target model) were (hx hy ) = (71 53). The Epanechnikov pro le (4) has been used for histogram computation, therefore, the mean shift iterations were computed with the uniform pro le. The target histogram has been derived in the RGB space with 32 32 32 bins. The algorithm runs comfortably at 30 fps on a 600 MHz PC, Java implementation. The tracking results are presented in Figure 1. The mean shift based tracker proved to be robust to partial occlusion, clutter, distractors (frame 140 in Figure 1), 2. Derive the weights fwi gi=1:::nh according to (25). 3. Based on the mean shift vector, derive the new location of the target (14) ^ y1 = Pnh i=1 xi wi g Pnh i=1 wi g 2 ^ y 0 ;x i h ^ y0;xi h 2 : (26) 4 and camera motion. Since no motion model has been assumed, the tracker adapted well to the nonstationary character of the player's movements, which alternates abruptly between slow and fast action. In addition, the intense blurring present in some frames and due to the camera motion, did not in uence the tracker performance (frame 150 in Figure 1). The same e ect, however, can largely perturb contour based trackers. 18 16 Mean Shift Iterations 14 12 10 8 6 4 2 0 50 100 150 Frame Index Figure 2: The number of mean shift iterations function of the frame index for the Football sequence. The mean number of iterations is 4:19 per frame. The number of mean shift iterations necessary for each frame (one scale) in the Football sequence is shown in Figure 2. One can identify two central peaks, corresponding to the movement of the player to the center of the image and back to the left side. The last and largest peak is due to the fast movement from the left to the right...
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