Automatic spin measurements for pitched Baseballs via consumer-grade high-speed cameras

Abstract

Controlling the spin of a ball is important in a variety of sports, especially baseball. For an athlete to properly train, it is necessary to know spin information immediately after throwing or hitting a baseball. This paper presents a fully automatic and marker-free technique to measure both the spin rate and spin axis of a pitched baseball using a consumer-grade high-speed camera. After tracking a ball from the high-speed video, our technique measures spin rate by detecting periods in which similar ball images appear, and then estimates spin axis by performing rigid registration that considers three-dimensional rotation. By separating the spin rate measurement and spin axis estimation processes, we achieve reasonable computational efficiency and robustness for small blurred baseball images extracted from video. We evaluated the accuracy of our presented technique by using synthesized videos. To illustrate the feasibility of our technique, we applied it to a variety of breaking ball pitches captured under normal outdoor lighting conditions.