[Opencv-python] cv2.threshold(...) Image threshold processing(2)

1. Background

Before reading this blog, please read the following blog:
[opencv-python] cv2.threshold(...) Image threshold processing (1)
https://blog.csdn.net/jn10010537/article/details/113811213

The python and cv2 versions of this blog are as follows:

python:3.6.8 (tags/v3.6.8:3c6b436a57, Dec 24 2018, 00:16:47) [MSC v.1916 64 bit (AMD64)]
opencv-python:4.5.1.48

Note: At present, the Otsu algorithm and the TRIANGLE algorithm only support single-channel image arrays of uint8 data type;