Linux

Let's see how to install OpenCV on Ubuntu. We need to install some dependencies before we begin. Let's install them using the package manager by running the following command in your Terminal:

$ sudo apt-get -y install libopencv-dev build-essential cmake libdc1394-22 libdc1394-22-dev libjpeg-dev libpng12-dev libtiff5-dev libjasper-dev libavcodec-dev libavformat-dev libswscale-dev libxine2-dev libgstreamer0.10-dev libgstreamer-plugins-base0.10-dev libv4l-dev libtbb-dev libqt4-dev libmp3lame-dev libopencore-amrnb-dev libopencore-amrwb-dev libtheora-dev libvorbis-dev libxvidcore-dev x264 v4l-utils 

Now that you have installed the dependencies, let's download, build, and install OpenCV:

$ wget "https://github.com/opencv/opencv/archive/4.0.0.tar.gz" -O opencv.tar.gz 
$ wget "https://github.com/opencv/opencv_contrib/archive/4.0.0.tar.gz" -O opencv_contrib.tar.gz 
$ tar -zxvf opencv.tar.gz 
$ tar -zxvf opencv_contrib.tar.gz 
$ cd opencv-4.0.0 
$ mkdir build 
$ cd build 
$ cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/full/path/to/opencv-4.0.0/build -D INSTALL_C_EXAMPLES=ON -D BUILD_EXAMPLES=ON -D OPENCV_EXTRA_MODULES_PATH=/full/path/to/opencv_contrib-4.0.0/modules ../ 
$ make -j4 
$ sudo make install 

Let's copy the pkgconfig file in opencv.pc to /usr/local/lib/pkgconfig, and name it opencv4.pc:

$ cp /full/path/to/opencv-4.0.0/build/lib/pkgconfig/opencv.pc /usr/local/lib/pkgconfig/opencv4.pc 

We're finished! We will now be able to use it to compile our OpenCV programs from the command line. Also, if you already have an existing OpenCV 3.x.x installation, there will be no conflict.

Let's check the installation is working properly:

$ cd /full/path/to/opencv-4.0.0/samples/cpp 
$ g++ -ggdb `pkg-config --cflags --libs opencv4` opencv_version.cpp -o /tmp/opencv_version && /tmp/opencv_version 

If you see Welcome to OpenCV 4.0.0 printed on your Terminal, you should be good to go. In the following chapters, we will learn how to use CMake to build our OpenCV projects.