opencv-contrib-python的安装：Set OPENCV_ENABLE_NONFREE CMake option and rebuild the library in function

问题描述

前往本页，可查看opencv-python和opencv-contrib-python的区别。
https://docs.opencv.org/master/

比如，SIFT就需要用到opencv-contrib-python包中的cv2.xfeatures2d。

解决方案

安装方式可见网址：
https://pypi.org/project/opencv-contrib-python/

1. 卸载opencv-python
   pip uninstall opencv-python
2. 安装opencv-contrib-python
   pip install opencv-contrib-python==3.4.2.17

注意第二步要指定版本，安装新版本有风险，可能有错误：Set OPENCV_ENABLE_NONFREE CMake option and rebuild the library in function 'create'等。