In PowerShell run:
$ pip3 install numpy
$ pip3 install matplotlib
Download OpenCV for Windows/Python here https://www.lfd.uci.edu/~gohlke/pythonlibs/#opencv I've tested 'https://download.lfd.uci.edu/pythonlibs/t4jqbe6o/opencv_python-4.1.0-cp37-cp37m-win_amd64.whl'
$ pip3 install ./opencv_python-4.1.0-cp37-cp37m-win_amd64.whl