Emgu/OpenCV: Event for VideoCapture.QueryFrame() finished.

Question

Here is the basic idea of my code:

    private void CaptureCameraFrame()
    {
        Capture = new VideoCapture();
        CameraModel.Instance.CameraViewMat = Capture.QueryFrame();

        // do stuff with queried matrix here

        if(noAbortCondition)
        {
            CaptureCameraFrame();
        }
    }

The method should run in a separate thread updating my GUI with the current image after processing. Only Problem is, that I get two different kinds of error:

1. Attempt to read/write protected memory: This happens on the second runthrough of the method.
2. I get an null-reference error using `CameraModel.Instance.CameraViewMat right after querying the frame.

The two issues seem to be connected, seems like QueryFrame() runs asynchronously from the rest of the code and isn't done when the program jumps to the next step. Question is: How can I make sure, that querying the image from the camera is finished, and I can use the information in the matrix as well as start a new query?

In all the examples I have found this is done by using time, but I would like to start with a new frame as soon as processing on the last frame is done.

I haven't really done much in C# when it comes to threading, but what I understand in such cases one would use the asyncand awaitkeywords to make sure a method in an asynchronous method is finished. However I wasn't able to make a working implementation in this case.

Answer 1

You are creating VideoCapture class instance repeatedly and even not disposing of it. Create your VideoCapture instance only once and use them for your task. At the end dispose it.

public YourConstructor()
{
    Capture = new VideoCapture();
}
private void CaptureCameraFrame()
{
    CameraModel.Instance.CameraViewMat = Capture.QueryFrame();

    // do stuff with queried matrix here

    if(noAbortCondition)
    {
        CaptureCameraFrame();
    }
}

Hopefully, it will work for you!