Color CCD camera calibration in virtual studio

摘要

In this paper, we describe some new methods to perform color CCD camera calibration in virtual studio. Our work is based on the pinhole camera model with lens radial distortion. Generally, the calibration problem consists of two steps: control points extraction from images and calibration algorithm implementation. For control point extraction, the usual way is relatively simple and can be easily done. But because of the poor quality of grabbed images and the lens distortion, the usual method has two main disadvantages in our virtual studio application. Hence we present an effective and robust method to perform control points extraction. Generally, the calibration experiments are implemented by Tsai's two-stage algorithm. But in our experiments, we find that the calibration problem is ill-conditioned, for the result is very sensible to tiny changes of calibration points' coordinates. To solve this problem, we present a new strategy to improve the accuracy of calibration results of focal length and depth. Then we obtain a focal length look-up-table (LUT) relative to the lens zoom rings. In virtual studio application, when the real camera pans or tilts, the background picture lags behind the foreground picture. Then a motion compensation model is presented to compensate the difference between the optical center and the real rotation center to overcome the problem.