2.1.4. Service Fault Detection Algorithm

The service height is determined by the maximum height of the shuttlecock when it is being hit by the racket during a badminton service. The hitting instant refers to the moment when the racket first comes into contact with the shuttlecock. Thus, the determination of the hitting instant is of utmost importance. In this work, the hitting instant (N^th frame) is determined by the large horizontal displacement of the shuttlecock as compared to the next frame (N+1^th frame). Since the rule of badminton mandates the whole of a shuttlecock to be below the 1.15 m height limit upon being hit, the highest point of the shuttlecock should then be used to evaluate whether the shuttlecock has exceeded the height limit. The highest point of the shuttlecock can be evaluated based on the N^th frame, as depicted in Figure 7.

Image sequences (acquired at 70 fps) showing the hitting instants in (a) backhand low serve and (b) forehand high serve situations and the determination of the shuttlecock’s maximum height at the hitting instant (N^th frame). The hitting instant (N^th frame) is determined by the large horizontal displacement of the shuttlecock as compared to the next frame (N+1^th frame).

An overview of the service fault detection system algorithm is depicted in Figure 8. Essentially, the acquired image from the camera is first resized to a dimension of 640 pixels × 640 pixels before feeding into the object detection model. This is vital because running inferences with the object detection model at the native image dimensions can severely slow down the inference speed. The output from the object detection model such as the label and the bounding box of the shuttlecock will be obtained and used to determine the displacement of the shuttlecock. The hitting event is then determined when a large horizontal displacement is detected. The height information about the shuttlecock at the hitting instant can then be evaluated based on the bounding box of the shuttlecock at the N^th frame, as depicted in Figure 7.

Overview of service fault detection algorithm.

The algorithm for detecting SFTH in badminton matches involves a series of steps: