'**SUMMARY**
Get each Pixel Velocity of the tracked object in pixel/frames.
**PARAMETERS**
No Parameters required.
**RETURNS**
* *numpy array* * - array of pixel velocity tuple.
>>> while True:
... img1 = cam.getImage()
... ts = img1.track("camshift", ts1, img, bb)
... img = img1
>>> print ts.pixelVelocity()'

def pixelVelocity(self):

    return np.array([f.vel for f in self])
