说明：  先用sobel算子对图像进行预处理，提取边缘。对于不连续的圆，在利用hough算法检测圆心坐标和半径，再将圆进行重画，得到完整的圆并显示。
(First with sobel operator for image pre-processing, edge extraction. For discontinuous circle detection algorithm using hough the center coordinates and radius, and then re-draw the circle, and displayed a complete circle.)