There're lots of guides out there but I'm gonna go ahead and point out this one. It worked for me and it's got a script, which you can modify and (re)use for a personalized install.
If you're on a Raspberry Pi, you might want to expand your swap space first, otherwise your make -j4 command might cause the system to run out if memory and stall:
sudo dphys-swapfile swapoff
As root, edit the file /etc/dphys-swapfile and modify the variable CONF_SWAPSIZE
sudo dphys-swapfile swapon
I prefer using cmake-gui, replacing the cmake command in the script. When installing OpenCV on my Pi, I had to disable all python and java related flags (because python and java modules were causing errors and I didn't need them anyway) and using cmake with GUI can help find and unset flags.
If you plan on using g++ or make to compile then make sure to set OPENCV_GENERATE_PKGCONFIG flag when running cmake during setup, so the opencv.pc file is generated (inside /usr/local/lib/pkgconfig).
Make sure that the line
export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig
is in your .bashrc file(and reboot).
You can use a Makefile like this (keep in mind there are better ones out there):
OPENCV = $(shell pkg-config --cflags --libs opencv4)
opencv_test:
g++ -std=c++11 -o opencv_test opencv_test.cpp $(OPENCV)
.PHONY: opencv_test
pkg-config will include what's inside /usr/local/include/opencv4 so you can use them in your code, for example:
#include "opencv2/aruco.hpp"
#include "opencv2/highgui/highgui.hpp"
since the opencv2 dir is inside the above path.
Below there are some specific notes for stuff I had to use or errors I ran into:
/** Notes
* dpkg -L <package_name> helps find packages
*/
-- Cmake can't find Qt5 --
CMake Error at cmake/OpenCVFindLibsGUI.cmake:18 (find_package): Could
not find a package configuration file provided by "Qt5" with any of
the following names:
Qt5Config.cmake qt5-config.cmake
Add the installation prefix of "Qt5" to CMAKE_PREFIX_PATH or set
"Qt5_DIR" to a directory containing one of the above files. If "Qt5"
provides a separate development package or SDK, be sure it has been
installed.
Solution from
https://askubuntu.com/questions/374755/what-package-do-i-need-to-build-a-qt-5-cmake-application
// install dev package
sudo apt install qtbase5-dev
