# Ubuntu install c++ version of OpenCV + opencv_contrib

* simple install OpenCV (不能指定版本-->不推薦)

sudo apt-get install libopencv-dev

* install dependency package

sudo apt-get install gcc g++ cmake pkg-config build-essential
sudo apt-get install libgtk2.0-dev libavcodec-dev libavformat-dev libtiff5-dev libswscale-dev libjasper-dev

* download the opencv package (use 3.4 version)

cd ~
git clone https://github.com/opencv/opencv.git

* configure OpenCV

cd opencv 
mkdir build
cd build
cmake -D CMAKE_BUILD_TYPE=Release -D OPENCV_GENERATE_PKGCONFIG=YES -D CMAKE_INSTALL_PREFIX=/usr/local ..

* make OpenCV

make -j4
sudo make install

* configure pkg-config

sudo vim /etc/ld.so.conf
加入: /usr/local/lib
sudo ldconfig -v
export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/local/lib/pkgconfig

* check opencv version

pkg-config --modversion opencv4

* configure opencv_contrib

cmake -D CMAKE_BUILD_TYPE=RELEASE -D OPENCV_EXTRA_MODULES_PATH=../opencv_contrib-3.4.5/modules ..

* make opencv_contrib

make -j4
sudo make install

___
* libopencv_core.so.3.4: cannot open shared object file: No such file or directory

sudo find / -name "libopencv_core.so.3.4"
sudo vim /etc/ld.so.conf.d/opencv.conf
加入: /usr/local/lib or /usr/local/lib/x86_64-linux-gnu
sudo ldconfig -v

___
* sample code

#include <opencv2/highgui.hpp>
#include <iostream>
int main( int argc, char** argv )
{
    cv::Mat image;
    image = cv::imread("lena.jpg",cv::IMREAD_COLOR);
    if(! image.data)
        {
            std::cout<<"Could not open file" << std::endl;
            return -1;
        }
    cv::namedWindow("lena", cv::WINDOW_AUTOSIZE);
    cv::imshow("lena", image);
    cv::waitKey(0);
    return 0;
}

___

* Reference
https://hackmd.io/@xpg109/H1wZiRUNF
https://bbs.huaweicloud.com/blogs/375024
https://blog.csdn.net/weixin_37950717/article/details/125222006
https://blog.csdn.net/DSK_981029/article/details/111143231
https://blog.csdn.net/jiexijihe945/article/details/126163341