[Opencv-python] cv2.flip(...) Image flip

1. Background

For detailed documentation, please refer to official information.
This blog is as simple and clear as possible. If there are any errors, please correct me.

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

Opencv provides the api for image flip:
you can flip a 2D array around the vertical axis (x axis), the horizontal axis (y axis) or two axes (xy axis).

cv2.flip(src, flipCode[, dst]