Install OpenCV4 from the source
Install OpenCv 4
Prerequisites
You need install some dep:
sudo apt install build-essential cmake git pkg-config libgtk-3-dev \
libavcodec-dev libavformat-dev libswscale-dev libv4l-dev \
libxvidcore-dev libx264-dev libjpeg-dev libpng-dev libtiff-dev \
gfortran openexr libatlas-base-dev python3-dev python3-numpy \
libtbb2 libtbb-dev libdc1394-22-dev
Install OpenCv 4
Go where you need to install opencv 4 lib
mkdir -p ~/dev/libs && cd ~/dev/libs/
git clone https://github.com/opencv/opencv.git -b 4.3.0
git clone https://github.com/opencv/opencv_contrib.git -b 4.3.0
mkdir opencv/build && cd opencv/build
cmake -DOPENCV_EXTRA_MODULES_PATH=../../opencv_contrib/modules ..
make -j$(nproc --all) && sudo make install
If you need to test
Let's imagin you have your code opencv files, go inside the folder.
mkdir build
cd build
cmake ..
make