Qt - Display topic image_raw on GUI

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A possible solution:

Your Qt program needs to to also be a ROS node, which is not a problem in principle. A caveat is that Qt needs to run in the main thread, so you need to put ros::spin() into it's own thread:

auto t = std::thread([&]() {
    ros::spin();
});

You may need not make sure you t.join() at the end of you main(...) and also handle ros::shutdown() and QCoreApplication::quit() in a custom signal handler.

Then I would recommend to convert the image into a cv::Mat with opencv_bridge and after that to a QImage by using the data pointer of cv::Mat. Something like that:

    QImage dest((const uchar *) cvmat.data, cvmat.cols, cvmat.rows, QImage::Format_RGB888);

The RGB888 assumes it is already debayered, image_raw is NOT debayered. You need to do it yourself, or use image_proc for that.

I also think that QImage takes owenership of the image data, so make sure you give it a copy that is not destroyed by some other destructor.

How to display a QImage in Qt is a question for a Qt forum. ;)