python调用cv2.findContours时报错：ValueError: not enough values to unpack (expected 3, got 2)

OpenCV旧版，返回三个参数：

im2, contours, hierarchy = cv2.findContours(mask, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
要想返回三个参数：

把OpenCV 降级成3.4.3.18 就可以了，在终端输入pip install opencv-python==3.4.3.18

OpenCV 新版调用，返回两个参数：

 contours, hierarchy = cv2.findContours(mask, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
---------------------
ref：https://blog.csdn.net/miao0967020148/article/details/88623631