PTZ Camera Network Calibration from Moving People in Sports Broadcasts

Abstract

In sports broadcasts, networks consisting of pan-tilt-zoom (PTZ) cameras usually exhibit very wide baselines, making standard matching techniques for camera calibration very hard to apply. If, additionally, there is a lack of texture, finding corresponding image regions becomes almost impossible. However, such networks are often set up to observe dynamic scenes on a ground plane. Corresponding image trajectories produced by moving objects need to fulfill specific geometric constraints, which can be leveraged for camera calibration. We present a method which combines image trajectory matching with the self-calibration of rotating and zooming cameras, effectively reducing the remaining degrees of freedom in the matching stage to a 2D similarity transformation. Additionally, lines on the ground plane are used to improve the calibration. In the end, all extrinsic and intrinsic camera parameters are refined in a final bundle adjustment. The proposed algorithm was evaluated both qualitatively and quantitatively on four different soccer sequences.