extractdigits

    Imgproc.findContours(cont, contours, hierarchy, Imgproc.RETR_CCOMP, Imgproc.CHAIN_APPROX_SIMPLE, new Point(0, 0));
        //cleanedMatList = new ArrayList<Mat>();
        //int c = 0;

    // points of the contours whose heights are bigger than the threshold
    List<Point> digits = new ArrayList<Point>();

    // don't iterate the hierarchy here. iterate the contours instead
        //for (int i = 0; i >= hierarchy.cols(); i++) {
    for (int i = 0; i < contours.size(); i++)
            Rect rect = Imgproc.boundingRect(contours.get(i));
            if (rect.height > HTRESH) {
        // this rectangle drawing in the binary image is only for visualization. it has nothing to do with final result
                Imgproc.rectangle(binary, new Point(rect.x, rect.y), new Point(rect.x + rect.width - 1, rect.y + rect.height - 1), new Scalar(0, 0, 255), 3);
                //cleanedMatList.add(c, binary);
                //c++;

        // append this contour points to digits list
        digits.addAll(contours.get(i).toList());
            }
        }
    // now we have all the digit contour points in digits list. now we can find the convexhull of these points

    // we dont need a convexhull for each contour. we need only one convexhull for the points in the digits list
        /*List<MatOfInt> digitsHull = new ArrayList<MatOfInt>();
        for(int i=0; i < contours.size(); i++){
            digitsHull.add(new MatOfInt());
        }
        for(int i=0; i < contours.size(); i++){
            Imgproc.convexHull(contours.get(i), digitsHull.get(i));
        }*/

    // get the convex hull
    MatOfInt digitsHullIdx = new MatOfInt();        // this contains the indices
    MatOfPoint hullPoints = new MatOfPoint();
    hullPoints.fromList(digits);
    Imgproc.convexHull(hullPoints, digitsHullIdx);

    // now you have to convert the convexhull digitsHullIdx into points to use it in a Imgproc.drawContours
    MatOfPoint digitsHullPoints = new MatOfPoint();
    // TODO: please find out how you can extract the points indexed by digitsHullIdx and add them to digitsHullPoints and do it here

    // now we have filled digitsHullPoints with points in the convexhull
        List<MatOfPoint> digitRegions = new ArrayList<MatOfPoint>();
    // digitsHullPoints to regions so we can use Imgproc.drawContours to create a mask
    digitRegions.add(digitsHullPoints);

    // digitRegions was just created and is empty, but you are iterating it. this has no effect
        /*for (int i = 0; i< digitRegions.size(); i++) {
            MatOfPoint dr = digitRegions.get(i);
            dr.push_back(digitsHull.get(i));
        }*/

        Mat digitsMask = new Mat(srcImage.rows(), srcImage.cols(), CvType.CV_8U);
        Imgproc.drawContours(digitsMask, digitRegions, 0, new Scalar(255, 255, 255), -1);
        Imgproc.morphologyEx(digitsMask, digitsMask, Imgproc.MORPH_DILATE, kernal);

        Mat cleaned = new Mat(srcImage.rows(), srcImage.cols(), CvType.CV_8U);
        diwb.copyTo(cleaned, digitsMask);

        return diwb;