cv2.error: OpenCV(4.4.0) /private/var/folders/nz/vv4_9tw56nv9k3tkvyszvwg80000gn/T/pip-req-build-gi6lxw0x/opencv/modules/imgcodecs/src/loadsave.cpp:738: error: (-215:Assertion failed) !_img.empty() in function 'imwrite' code example

Example: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'

This error happened because the image didn't load properly.
So you have problem with the previous line cv2.imread my suggestion is :

check if the images exist in the path you give

check the count variable if he have valid number