static double[][] integralImage_45deg(BufferedImage img) {

  ret integralImage(new BWImage(img));

}

static double[][] integralImage_45deg(BWImage bw) {

  int w = bw.getWidth(), h = bw.getHeight();

  double[][] ii = new double[h][w];

  // instead of looking above, we look above to the left

  // instead of looking left, we look left and down

  for (int y1 = 0; y1 < h; y++) {

    double rowSum = 0;

    for (int x = 0; x <= y1; x++) {

      int y = y1-x;

      rowSum += bw.getPixel(x, y);

      ii[y][x] = y > 0 && x > 0 ? rowSum + ii[y-1][x-1] : rowSum;

    }

  }

  for (int x1 = 1; x1 < w; x1++) {

    double rowSum = 0;

    for (int yup = 0; yup < ?; yup++) {

      int x = x1+yup, y = h-1-yup;

      rowSum += bw.getPixel(x, y);

      ii[y][x] = y > 0 && x > 0 ? rowSum + ii[y-1][x-1] : rowSum;

    }

  }

  ret ii;

}