opencv下载地址
opencv以及opencv_contrib在github上面的下载地址：
使用github clone下载
git clone https://github.com/opencv/opencv.git
cd opencv
git checkout 3.4.0
git clone https://github.com/opencv/opencv_contrib.git
cd opencv_contrib
git checkout 3.4.0对应版本号：3.4.0（修改想要的就行）
https://github.com/opencv/opencv_contrib/tree/3.4.0
https://github.com/opencv/opencv/tree/3.4.0
最新版本号：
https://github.com/opencv/opencv_contrib/tree/master/
https://github.com/opencv/opencv/tree/master/
下载离线包：
https://github.com/Itseez/opencv/archive/3.4.0.zip
https://github.com/Itseez/opencv_contrib/archive/3.4.0.zip
最后将opencv_contrib解压到opencv文件夹，网上教程大多是嵌套，其实可直接合并再编译。
安装参考地址：
https://www.learnopencv.com/install-opencv3-on-ubuntu/
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