I am new to OpenCV and trying to detect aruco marker from https://chev.me/arucogen/ using android Java

Question

Hi i am new to OpenCV and trying to to detect aruco marker from https://chev.me/arucogen/

but corner.size() always returns 4 if there is only 3 markers in picture.

 Log.d("testCorner: "," hitted image capture "+image);
                    final Bitmap bitmap = textureView.getBitmap();

                    if (bitmap == null)
                        return;

                    Mat rgba = new Mat();
                    Utils.bitmapToMat(bitmap, rgba);

                    rgb = new Mat();
                    Imgproc.cvtColor(rgba, rgb, Imgproc.COLOR_RGBA2RGB);

                    gray = new Mat();
                    Imgproc.cvtColor(rgba, gray, Imgproc.COLOR_RGBA2GRAY);

                    Utils.matToBitmap(rgb, bitmap);
                    image.close();
                    detectArucoCode(gray, bitmap);
Detecting Aruoco code() ->function
   ids = null;
    ids = new MatOfInt();
    if (corners != null)
        corners.clear();
    Aruco.detectMarkers(mat, dictionary, corners, ids, parameters);
    Log.d("ITC: IDs", ids.dump());
    Log.d("ITC: corners", ""+corners.size());
    if (corners != null)
        Log.d("testCorner: "," "+corners.size());

Its really appreciable for all replies