cv2.rectangle(image,p1,p2,color,thickness) 参数：thickness线宽，当为正值时函数在图上绘制宽度为thickness的矩形框，为负值绘制填充的矩形。

cv2.rectangle(board, (min_x, min_y), (max_x, max_y), (255, 255, 255), thickness=-1)