// doesn't clean the coordinates
static BufferedImage ii_clip(IntegralImage img, int x1, int y1, int w, int h) {
  if (img == null) null;
  BufferedImage out = newBufferedImage(w, h);
  for y to h:
    for x to w:
      out.setRGB(x, y, ii_getPixel(img, x1+x, y1+y));
  ret out;
}

static BufferedImage ii_clip(IntegralImage ii, DoubleRect r) {
  ret ii_clip(ii, toRect(r));
}

static BufferedImage ii_clip(IntegralImage ii, Rect r) {
  ret r == null ? null : ii_clip(ii, r.x, r.y, r.w, r.h);
}