解决:ValueError: not enough values to unpack (expected 3, got 2)
错误原因:cv2.findContours的opencv旧版本返回3个值:im2,contours,hierarchy=cv2.findContours(mask,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE),新版本返回2个值:contours,hierarchy=cv2.findContours(mask,cv2.RETR_TREE,cv2.CHAIN_APPRO