Android Canny problem No implementation found

edit

can you please explain how to install opencv 3.3.1 or higher using adb ? i can't even find the apk to install and neither a tuto ti do it.

Unfortunately I think it is not the problem. My code is:

public List<MatOfPoint> biggestContourSegmentation(Mat img) {
    edges = new Mat();
    Imgproc.Canny(img, edges, 30.0, 200.0);

I do believe that it uses

//javadoc: Canny(image, edges, threshold1, threshold2)
public static void Canny(Mat image, Mat edges, double threshold1, double threshold2)
{

    Canny_3(image.nativeObj, edges.nativeObj, threshold1, threshold2);

    return;
}

form Imgproc package and the native class that java calls is actually taking long values:

private static native void Canny_3(long image_nativeObj, long edges_nativeObj, double threshold1, double threshold2);