Install OpenCV 4.5 on Ubuntu 22.04

OpenCV (Open Source Computer Vision Library) is a library of programming functions mainly for real-time computer vision.

But its installation can be very tricky in an environment like Linux, so let’s follow a correct installation process.

Download the sources

The most recent release at the time of writing is 4.5.1.

Create a tmp folder for all the archives:

mkdir ~/opencv4.5-tmp && cd ~/opencv4.5-tmp

Download the OpenCV sources and the opencv-contrib sources:

wget https://github.com/opencv/opencv/archive/4.5.1.zip -O opencv.zip
wget https://github.com/opencv/opencv_contrib/archive/4.5.1.zip -O opencv_contrib.zip

Unzip both archives:

unzip opencv.zip
unzip opencv_contrib.zip

Move the files to simpler directory names:

mv opencv-4.5.1/ opencv
mv opencv_contrib-4.5.1/ opencv_contrib

Build and install

Make a build directory:

cd opencv && mkdir build && cd build

Copy and run the following command (install cmake first if it is not available on your system):

cmake -D CMAKE_BUILD_TYPE=DEBUG \
      -D CMAKE_INSTALL_PREFIX=~/opencv4.5-custom \
      -D OPENCV_EXTRA_MODULES_PATH=~/opencv4.5-tmp/opencv_contrib/modules \
      -D OPENCV_GENERATE_PKGCONFIG=ON \
      -D BUILD_EXAMPLES=ON ..

Make the project:

make -j4

Install OpenCV:

sudo make install

Ensure it is updated in the library storage:

sudo ldconfig

Configure a C++ project to work with OpenCV

Open your editor of choice (vim in my case), create a folder ~/projects/HelloOpenCV, and put your code in main.cpp.

First, let’s try to compile the application with g++ as usual:

g++ -Wall -o main main.cpp

We see that it cannot find our library headers.

For that we need to provide the path to the headers and the linker flags. The best way to find them all in one place is the pkg-config utility. Remember we provided an additional argument to our cmake generation? So let’s execute the following:

export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/home/parallels/opencv4.5-custom/lib/pkgconfig
pkg-config --cflags --libs opencv4

Now add all the flags to the compilation command:

g++ -Wall -o main main.cpp $(pkg-config --cflags --libs opencv4)

Or a more explicit version for our particular sample:

g++ -Wall -o main main.cpp \
   -I/home/parallels/opencv4.5-custom/include/opencv4 \
   -L/home/parallels/opencv4.5-custom/lib \
   -lopencv_highgui -lopencv_videoio -lopencv_imgcodecs -lopencv_core