how to use matrices with asynctasks?

Question

I am relative new to java and i need help to use matrix with async Task. I am using input frame from onCameraFrame to analysis in background. I will provide the method and async Task.

 public int recognize(Mat inputFrame) {
    int detector=0;
    Mat gray= inputFrame;
    if (startedFrame){
        BRISK.detect(inputFrame,keypoints1);
        BRISK.compute(inputFrame,keypoints1,deskriptor1);
        startedFrame=false;
        return 0;
    }

    BRISK.detect(inputFrame,keypoints2);
    BRISK.compute(inputFrame,keypoints2,deskriptor2);

    List<MatOfDMatch> matches = new LinkedList<MatOfDMatch>();
    matcher.knnMatch(deskriptor1, deskriptor2, matches,2);
    //Calculating good match list...
    LinkedList<DMatch> goodMatchesList = new LinkedList<DMatch>();

    for (int i = 0; i < matches.size(); i++) {
        MatOfDMatch matofDMatch = matches.get(i);
        DMatch[] dmatcharray = matofDMatch.toArray();
        DMatch m1 = dmatcharray[0];
        DMatch m2 = dmatcharray[1];

        if (m1.distance <= m2.distance * nndrRatio) {
            goodMatchesList.addLast(m1);

        }
    }
    if (goodMatchesList.size() >= 7) {

        List<KeyPoint> controlKeypointlist = keypoints1.toList();
        List<KeyPoint> liveKeypointlist = keypoints2.toList();

        LinkedList<Point> objectPoints = new LinkedList<>();
        LinkedList<Point> scenePoints = new LinkedList<>();

        for (int i = 0; i < goodMatchesList.size(); i++) {
            objectPoints.addLast(controlKeypointlist.get(goodMatchesList.get(i).queryIdx).pt);
            scenePoints.addLast(liveKeypointlist.get(goodMatchesList.get(i).trainIdx).pt);
        }

        MatOfPoint2f objMatOfPoint2f = new MatOfPoint2f();
        objMatOfPoint2f.fromList(objectPoints);
        MatOfPoint2f scnMatOfPoint2f = new MatOfPoint2f();
        scnMatOfPoint2f.fromList(scenePoints);
        detector=1;
        keypoints2.release();
        deskriptor2.release();
        return 2;

    }
    return 1;
}
class MyTask extends AsyncTask<Mat, Void, Integer> {


    @Override
    protected Integer doInBackground(Mat... mats) {
        return recognize(mats);
    }
}

And problem is in return recognize(mats); ,in parametar mats where it say:recognize (org.opencv.core.Mat) in MainActivity cannot be applied to (org.opencv.core.Mat[]) and i do not know how to solve it?Thanks in advance.

Answer 1

The parameter Mat... is a varargs parameter and acts like an array. (ie Mat[] ).

To get the first Mat of the arguments use mats[0] :

@Override
protected Integer doInBackground(Mat... mats) {
    return recognize(mats[0]);
}

Answer 2

In Java Mat... represents an array of Mat class type. If you look at the error

recognize (org.opencv.core.Mat) in MainActivity cannot be applied to (org.opencv.core.Mat[])

You'll notice that it says exactly the same thing ie you are passing an Array to a method which takes a single instance. So all you need to do is:

return recognize(mats[0]);

get the Mat at the first index of this array.