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OpenCV (Java) : Draw a rectangle region on Camera View

I 'm trying to create a bank card scanner on android using OpenCV, first, I'm creating a region where the user can scan their cards then crop it after, I'm struggling with the rectangle region and place it on the center, Any suggestion on how I can do it? Thank you so much

Here's what I've done so far:

It's doing a rectangle and its centered but the size isn't enough I tried to change the numbers but the position isn't centering.

 public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
        Mat mrgba = inputFrame.rgba();

        int w = mrgba.width();
        int h = mrgba.height();

        Imgproc.rectangle(mrgba, new Point(w * 1 / 3, h * 1 / 3), new Point(
                w * 2 / 3, h * 2 /  3 ), new Scalar( 255, 0, 0 ), 5

        return mrgba;


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