static BufferedImage grayImageFromIBWIntegralImage(IBWIntegralImage img) {
  int w = img.getWidth(), h = img.getHeight();
  byte[] pixels = new[w*h];
  int i = 0;
  for y to h:
    for x to w: {
      int pixel = img.getPixelBrightness(x, y);
      ifdef grayImageFromIBWIntegralImage_debug
        if (x == 0 && y == 0) print(+pixel);
      endifdef
      pixels[i++] = clampToUByte(pixel;
    }
  ret newGrayBufferedImage(w, h, pixels);
}