Android : OpenCv android : Copy part of an image to new Mat

I am new to OpenCv and trying to learn by implementing. I need to draw the contours i have detected in new Mat so I can work with them.

This is my Original image

After doing some work I achieved this by finding and drawing contours

Here's my code

                m = Utils.loadResource(MainActivity.this, R.drawable.sheet1, Highgui.CV_LOAD_IMAGE_COLOR);
                Bitmap bm = Bitmap.createBitmap(m.cols(), m.rows(),Bitmap.Config.ARGB_8888);

                Imgproc.cvtColor(m, m, Imgproc.COLOR_BGR2GRAY);
                Imgproc.medianBlur(m, m, 3);
                Imgproc.threshold(m, m, 0, 255, Imgproc.THRESH_OTSU);
                Core.bitwise_not(m, m);
                Imgproc.dilate(m, m, Imgproc.getStructuringElement(Imgproc.MORPH_RECT, new Size(1,118)));

                //Contours detection

                java.util.List<MatOfPoint> contours = new ArrayList<MatOfPoint>();

                Imgproc.findContours(m, contours, new Mat() ,Imgproc.RETR_EXTERNAL , Imgproc.CHAIN_APPROX_SIMPLE);
                Imgproc.cvtColor(m, m, Imgproc.COLOR_GRAY2BGR);

                //Contour drawing

                Mat matArray = new Mat();

                Imgproc.drawContours(m, contours, -1, new Scalar(153,255,204), 3);

                Utils.matToBitmap(m, bm);
                ImageView iv = (ImageView) findViewById(R.id.imageView1);
                iv.setImageBitmap(bm);

Now, I want to save every MCQ in new Mat.How can this be implemented in android Java?