Sports camera calibration using flexible intersection selection and refinement

Abstract

Sports scene analysis is an important technology to quantify a player’s action and visualize game statistics. To realize such technology, camera calibration is required to recognize the player’s position from a video. In this paper, we propose an automatic camera calibration method by using intersection resorting and refinement. Our contributions are 1) flexible intersection selection and 2) intersection refinement to improve accuracy in calibration. A homography matrix is used to convert world coordinates to image coordinates for the calibration. Sports scenes can be estimated by using a priori information such as length and position of field lines and their intersections. Conventional methods using the field lines and intersections cannot realize sufficient calibration accuracy because the intersections are selected from the combination of horizontal and vertical lines. Moreover, displacement at the intersections occurs between the detected position and a real one on the input image. Our proposed method can solve these problems by flexible intersection selection and refinement. As a result, a player’s position in the real world is identified from the video by using the estimated homography matrix. Our experimental results show that the proposed method achieves higher accuracy than that by conventional methods.