OpenCV build steps:
download opencv and contrib
1, CMake 3.16.1, python 3.7
2, Create build folder
3, Click Configure
4, Search test and java, remove
5, Search "free", select OPENCV_ENABLE_NOFREE
6, Search extra_modules_path, select to opencv_contrib path to module folder
7, search world, select to build dll one for all, otherwise don't select
8, Click configure again and again.
9, click Generate
10, open vs project such as Opencv.sln
11, Build->batch build-> select build all(debug and release) and install(debug and release)
12, usefull file in install folder