OpenCV integration with Qt6

[Christian Ehrlicher]

D:\opencv-build != D:\opencv-4.x.build

[Catman]

@Christian-Ehrlicher Act like they are the same, I tried to install OpenCV like 20 times after the original post and this CMake Image is just more recent.

[Christian Ehrlicher]

You Selected the wrong generator (Visual Studio) and not the Makefile generator and therefore a VS solution file was created. Remove the build dir, make sure no vsvars*.bat is not called so cmake does not pick up MSVC and call cmake with '-G MinGW Makefiles'

[Catman]

@Christian-Ehrlicher I'm new to Cmake what do you mean by
"make sure no vsvars*.bat is not called"

I think what you mean is that I just have to change my generator to MinGW Makefile, but then:
In the console above ^
'Release' build type is used by default. Use CMAKE_BUILD_TYPE to specify build type (Release or Debug)
CMake Error: CMake was unable to find a build program corresponding to "MinGW Makefiles". CMAKE_MAKE_PROGRAM is not set. You probably need to select a different build tool.
CMake Error: CMake was unable to find a build program corresponding to "MinGW Makefiles". CMAKE_MAKE_PROGRAM is not set. You probably need to select a different build tool.
Configuring incomplete, errors occurred!

[cristian-adam]

The https://wiki.qt.io/How_to_setup_Qt_and_openCV_on_Windows page is outdated and doesn't apply to Qt6 anymore.

That page needs to be rewritten to deal with CMake, Qt6 and having a OpenCV CMake example.

I think the easiest way of dealing with 3rd party dependencies would be to use a source package manager like conan, vcpkg or cpp-pm.

[mchinand]

In a terminal, add the MinGW's bin directory to your path and then start the cmake_gui from that terminal. e.g., set PATH=D:\Qt\Tools\mingw1120_64\bin;%PATH%. That way, CMake should be able to find the compiler, make, etc.

[cristian-adam]

I just tested Qt 6.2.3, OpenCV 4.5.5 with MinGW 11.2.0, and everything worked as expected 🙂

I used CMake 3.21.3 (but any recent version should be fine) and Ninja 1.10.2.

Compiling OpenCV

I've extracted the OpenCV source package into c:\Projects\opencv\opencv-4.5.5.

Then I've opened a command prompt window and set the environment:

set PATH=c:\mingw64\bin;c:\tools\ninja;c:\tools\cmake\bin;%PATH%

Your paths might vary so update accordingly.

Then configured OpenCV:

cd c:\Projects\opencv
cmake -G Ninja -D CMAKE_BUILD_TYPE=Release -S opencv-4.5.5 -B build-opencv -D WITH_QT=ON -D CMAKE_PREFIX_PATH=C:/Qt/6.2.3/mingw_64

Then built OpenCV:

cmake --build build-opencv

And installed OpenCV

cmake --install build-opencv --prefix opencv-install

Using OpenCV

I've created test-qt CMake Qt Widgets example.

In CMakeLists.txt I have added:

find_package(OpenCV REQUIRED)

This command finds the OpenCV CMake package and sets some CMake variables which I used for the test-qt executable target:

target_include_directories(test-qt PRIVATE ${OpenCV_INCLUDE_DIRS})
target_link_libraries(test-qt PRIVATE ${OpenCV_LIBS})

And in the CMake project settings I have changed the CMAKE_PREFIX_PATH in Initial Configuration to:

%{Qt:QT_INSTALL_PREFIX};c:\Projects\opencv\opencv-install

Then in mainwindow.cpp I've added the OpenCV headers:

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>

and in the constructor the OpenCV usage:

    // read an image
    cv::Mat image = cv::imread("c:/Windows/Web/Wallpaper/Windows/img0.jpg", 1);
    // create image window named "Wallpaper"
    cv::namedWindow("Wallpaper");
    // show the image on window
    cv::imshow("Wallpaper", image);

Then compiled and run my application in Qt Creator 7.0.1. 🎉

[Catman]

@cristian-adam
It really works and it wasn't that hard, your instructions were simple and clear.
I Highly appreciate your effort, and I hope you wonderful day/night :).

[Morgan7794]

@cristian-adam said in OpenCV integration with Qt6:

Using OpenCV
I've created test-qt CMake Qt Widgets example.
In CMakeLists.txt I have added:
find_package(OpenCV REQUIRED)

This command finds the OpenCV CMake package and sets some CMake variables which I used for the test-qt executable target:
target_include_directories(test-qt PRIVATE ${OpenCV_INCLUDE_DIRS})
target_link_libraries(test-qt PRIVATE ${OpenCV_LIBS})

And in the CMake project settings I have changed the CMAKE_PREFIX_PATH in Initial Configuration to:
%{Qt:QT_INSTALL_PREFIX};c:\Projects\opencv\opencv-install

Hey brother, I don't quite understand the specific operation here. Could you please guide me? Thank you

[Bondrusiek]

@Morgan7794 hi please see this example: https://github.com/FelgoSDK/Qt-Felgo-OpenCV maybe it helps you.

[DeSa]

@cristian-adam After spending 6 hours trying to set up OpenCV with Qt6 while following several tutorials (only to find out that it all does not apply to Qt6), your solution worked perfectly fine.

I should only add that I struggled with Qt Creator GUI looking for cmake project settings to change CMAKE_PREFIX_PATH. but finally got it (CTRL+5) ,
Just bookmarked this thread for good.

many thanks for this!