This single template allows to use OpenCV into a QT applicatio (QMainWindow based). Some aspects to be considered:

• Initially, the project was created using QT Creator. However, I am not fan of that IDE/environment (actually I hate it). That is the reason that project contains a .pro file
• Next, the QT Designer was used it just to place a single Label widget
• Project is generated to work using Visual Studio. Then a CMake file is created manually (don't worry, it works)
• Files mainview.* are related to the graphical interface

File mainview.cpp contains the code to display an image, loading a simple image

You need an image called small.png in the same location of the source/headers files (aka, the root). Actually, you must to change that!

OpenCVinQT requires CMake to create the environment (I used the version 3.10). Also, I used Visual Studio 2017 as IDE, and QT version 5.10, and VTK version 8.0.1 (December, 2017).

Using a label to render/display an OpenCV image, is not a good approach (actually is a very bad approach! due that is slow and not resizable).

Walter Lucetti offers a better approach using OpenGL to render the image getting a faster, adjustable and coherent way to do that.

Of course, that is not the only approach available. Google has a simple multithreaded OpenCV example application using the Qt framework which looks very nice to test and to incorporate into projects.