JKQtPlotter/examples/rgbimageplot_qt/README.md

Example (JKQTPlotter): QImage as a Graph

This project (see ./examples/rgbimageplot_qt/) simply creates a JKQTPlotter widget (as a new window) and adds an image plot with an image taken from a QImage object.

The source code of the main application is (see rgbimageplot_qt.cpp. the main parts are:

    // 2. now we open a BMP-file and load it into an OpenCV cv::Mat
    QImage image(":/example.bmp");

    // 3. create a graph (JKQTPImage) with a pointer to the QImage-object, generated above
    JKQTPImage* graph=new JKQTPImage(&plot);
    graph->setTitle("");
    // copy the image into the graph (optionally you could also give a pointer to a QImage,
    // but then you need to ensure that the QImage is available as long as the JKQTPImage
    // instace lives)
    graph->setImage(image);
    // where does the image start in the plot, given in plot-axis-coordinates (bottom-left corner)
    graph->setX(0);
    graph->setY(0);
    // width/height of the image in plot coordinates
    graph->setWidth(image.width());
    graph->setHeight(image.height());

    // 4. add the graphs to the plot, so it is actually displayed
    plot.addGraph(graph);

The result looks like this:

The image is upside-down, because computer images use a coordinate system with 0 at the top-left (left-handed coordinate system) and the JKQTPlotter has its 0 at the bottom-left (right-handed coordinate system).

You can modify the program above to display the image in the correct orientation, by adding the line

    // 6.1 invert y-axis, so image is oriented correctly
    plot.getYAxis()->setInverted(true);

This will reorient the y-axis to point from top to bottom (for increasing positive coordinates):