// Hilditch
        public void getHilditchThinningImage(Bitmap img) {
        int a, b;
        boolean hasChange;

        int width = img.getWidth();
        int height = img.getHeight();

        getBlackAndWhite(img, 128);

        do {
            hasChange = false;

            for (int i = 1; (i + 2) < width; i++) {
                for (int j = 1; (j + 2) < height; j++) {
                    a = getA(img, i, j);
                    b = getB(img, i, j);

                    int p1 = get01Pixel(img.getPixel(i, j));
                    int p2 = get01Pixel(img.getPixel(i, j - 1));
                    int p4 = get01Pixel(img.getPixel(i + 1, j));
                    int p6 = get01Pixel(img.getPixel(i, j + 1));
                    int p8 = get01Pixel(img.getPixel(i - 1, j));

                    if (p1 == 1 && b >= 2 && b <= 6 && a == 1
                            && ((p2 * p4 * p8) == 0 || getA(img, i, j - 1) != 1)
                            && ((p2 * p4 * p6) == 0 || getA(img, i + 1, j) != 1))
                    {
                        int color = Color.rgb(255, 255, 255);
                        img.setPixel(i, j, color);

                        hasChange = true;
                    }
                }
            }
        } while (hasChange);
    }

// ZhangSuen
    public void getZhangSuenThinningImage(Bitmap img) {
        int a, b;
        ArrayList<Point> pointsToChange = new ArrayList<>();
        boolean hasChange;

        int width = img.getWidth();
        int height = img.getHeight();

        getBlackAndWhite(img, 128);

        do {
            hasChange = false;

            for (int i = 1; (i + 1) < width; i++) {
                for (int j = 1; (j + 1) < height; j++) {
                    a = getA(img, i, j);
                    b = getB(img, i, j);

                    int p1 = get01Pixel(img.getPixel(i, j));
                    int p2 = get01Pixel(img.getPixel(i, j - 1));
                    int p4 = get01Pixel(img.getPixel(i + 1, j));
                    int p6 = get01Pixel(img.getPixel(i, j + 1));
                    int p8 = get01Pixel(img.getPixel(i - 1, j));

                    if (p1 == 1 && b >= 2 && b <= 6 && a == 1
                            && ((p2 * p4 * p6) == 0)
                            && ((p4 * p6 * p8) == 0))
                    {
                        pointsToChange.add(new Point(i, j));
                        hasChange = true;
                    }
                }
            }

            for (Point point : pointsToChange) {
                int color = Color.rgb(255, 255, 255);
                img.setPixel(point.getI(), point.getJ(), color);
            }

            pointsToChange.clear();

            for (int i = 1; (i + 1) < width; i++) {
                for (int j = 1; (j + 1) < height; j++) {
                    a = getA(img, i, j);
                    b = getB(img, i, j);

                    int p1 = get01Pixel(img.getPixel(i, j));
                    int p2 = get01Pixel(img.getPixel(i, j - 1));
                    int p4 = get01Pixel(img.getPixel(i + 1, j));
                    int p6 = get01Pixel(img.getPixel(i, j + 1));
                    int p8 = get01Pixel(img.getPixel(i - 1, j));

                    if (p1 == 1 && b >= 2 && b <= 6 && a == 1
                            && ((p2 * p4 * p8) == 0)
                            && ((p2 * p6 * p8) == 0))
                    {
                        pointsToChange.add(new Point(i, j));
                        hasChange = true;
                    }
                }
            }

            for (Point point : pointsToChange) {
                int color = Color.rgb(255, 255, 255);
                img.setPixel(point.getI(), point.getJ(), color);
            }

            pointsToChange.clear();
        } while (hasChange);
    }