  Electronic Line Calling is an auxiliary referee system used for tennis
matches based on binocular vision technology. While ELC has been widely used,
there are still many problems, such as complex installation and maintenance,
high cost and etc. We propose a monocular vision technology based ELC method.
The method has the following steps. First, locate the tennis ball's trajectory.
We propose a multistage tennis ball positioning approach combining background
subtraction and color area filtering. Then we propose a bouncing point
prediction method by minimizing the fitting loss of the uncertain point.
Finally, we find out whether the bouncing point of the ball is out of bounds or
not according to the relative position between the bouncing point and the court
side line in the two dimensional image. We collected and tagged 394 samples
with an accuracy rate of 99.4%, and 81.8% of the 11 samples with bouncing
points.The experimental results show that our method is feasible to judge if a
ball is out of the court with monocular vision and significantly reduce complex
installation and costs of ELC system with binocular vision.
