在运行opencv的python代码时，调用cv2.imshow时报错，如下所示
cv2.imshow(opencv_title, out)
cv2.error: OpenCV(4.5.5) D:\a\opencv-python\opencv-python\opencv\modules\highgui\src\window.cpp:1268: 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'
先用以下命令，查看opencv安装情况
pip list结果如图所示，opencv和contrib库都有安装，且版本一致。
几经周折，查到问题解决方法，参考https://github.com/opencv/opencv-python/issues/18
卸载掉opencv-python-headless即可
pip uninstall opencv-python-headless卸载完应该就可以正常运行了。
如果仍然无法运行，如以下报错：
AttributeError: module 'cv2' has no attribute 'imread'
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则先全卸载
pip uninstall opencv-python
pip uninstall opencv-contrib-python再安装
pip install opencv-contrib-python
pip install opencv-python应该就不会再报错了。
注意再安装时的版本最好与之前一致，否者可能导致与其它库版本不兼容的情况。