OpenCV integration with Qt6

Catman

Hello I've wasted several hours searching web to find solution for my problem and couldn't find anything useful

I've been following this tutorial: https://wiki.qt.io/How_to_setup_Qt_and_openCV_on_Windows and I don't understand what is not working

every single time I tried no matter if I've used Qt6/Qt5, CMake 3.7.2/CMake3.23.1, OpenCV3.4.15/Open4.5.5, Nothing seems to work at all. every single time I get Stuck on this part.
help

SGaist

Hi and welcome to devnet,

From what you show in your screenshot, cmake was not run.

cmake is required to setup the build instructions then make to execute these instructions.

Catman

@SGaist As far as I understand how it all works, I configured and generated everything in Cmake succesfuly
asdasdasdasdasdasdasddsaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.png ]

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The https://wiki.qt.io/How_to_setup_Qt_and_openCV_on_Windows page is outdated and doesn't apply to Qt6 anymore.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

QtWS: Super Early Bird Tickets Available!

OpenCV integration with Qt6

Compiling OpenCV

Using OpenCV