Understanding Sports Video Using Players Trajectories - Intelligent Video Event Analysis and Understanding - page 137

Fig. 6 Two frames taken from the squash video used for experiments (the entire video is
composed of 15508 frames). Ground truth activity for left and right images are respectively
“rally” and “passive”.
Fig. 7 Left: training trajectories of 2 squash players in the video plane (in green and ma-
genta) during the first half (corresponding to 7422 images) of a squash video. Right: test
trajectories of 2 squash players (in blue and red) during the second half of the squash video
(corresponding to 8086 images).
player hits the ball out). The “passive” phase corresponds to periods between the end
of a point and the beginning of the following point, and contains (despite its name)
an important activity. Indeed between two points, one of the player has to reach
and take the ball and then players may change positions whether the server won the
point or not. Furthermore, on the contrary to beginners that do not have efficient
displacements, professional players (such that those in the processed squash video)
usually only have low motion activity during the “rally” phase. Position of the play-
ers are more important than their mobility, i.e. , they place themselves to optimize
their displacements in order to easily and quickly reach the ball while keeping from
tiredness.