Exertion Interfaces: Sport over a Distance for Social bonding ...
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3 D E S I G N A N D I M P L E M E N T A T I O N
3.6.1.2.3 Detection Algorithm
The detection algorithm to determine the ball in the image is
identical for both cameras. Firstly, an image subtraction is performed
between the current and the previous frame to detect differences in
the image. These differences can be seen in Figure 17, which shows
the ball. If the ball was detected in the previous frame, the difference
image would also detect the non-existence of the ball at its previous
location, resulting in two detected balls in the picture: where the ball
is in the current frame, and where it used to be in the previous frame.
To avoid this ambiguity, the difference frame is only calculated
using the previous frame if there was no ball detected in it. If there
was a ball detected, the most recent frame that did not contain a ball
was used. Alternatively, one could compare each frame to the very
first one, which could be deliberately arranged to be noise free.
However, if during the game the background or the lighting changes,
these differences will be continuously detected in every frame,
causing wrong detections. Therefore, the former design was favored,
and the resulting detection software is very robust against these
Figure 17
Ball detected from
the top view
camera
Exertion Interfaces: Sports over a Distance for Social Bonding and Fun
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Summary :
If the ball was detected in the previous frame, the difference image would also detect the non-existence of the ball at its previous location, resulting in two detected balls in the picture: where the ball is in the current frame, and where it used to be in the previous frame.
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ball,frame,detected,preious,image,differences,detection,difference,detect,current,resulting,figure,ery