use sol2 to bind the opencv library

[libaineu2004]

https://opencv.org/

I want to use sol2 to bind the opencv library.
But I don't know how to implement it?
For example, reading and binarizing images.

cv::Mat src = cv::imread("demo.png", IMREAD_GRAYSCALE);
cv::Mat dst;
cv::threshold(src, dst, 128, 255, THRESH_BINARY);
cv::imshow("binary", dst);

Could you please write an example? How to bind opencv? I want to use lua to implement this C++ source code.
Thank you!