History, I have been running OpenCV on Raspbian Stretch in a virtual environment for a couple of years. Due to the requirement to add functionality for a PS4 controller I switched to Raspbian Buster. I re-installed OpenCV 4.5.1 (opencv-contrib-python) using the PyImageSearch pip guide here
Now, I have been tryinig to run some of my known working OpenCV python programs, remote headless using vncserver and vncviewer (Mac) and with a monitor and kbd attached, but keep getting the following error:
cv2.error: OpenCV(4.5.1) /tmp/pip-install-hyt7ii05/opencv-contrib-python_3f506ec0b739451b84e2498020092625/opencv/modules/highgui/src/window.cpp:651: error: (-2:Unspecified error) The function is not implemented. Rebuild the library with Windows, GTK+ 2.x or Cocoa support. If you are on Ubuntu or Debian, install libgtk2.0-dev and pkg-config, then re-run cmake or configure script in function 'cvShowImage'
Any ideas on the correct way to solve this - I understand I need to install libgtk and pkg-config, but want to do it correctly.