static L<Rect> bwAutoCropClips(BWImage bw, L<Rect> clips) {
  new L<Rect> l;
  for (Rect clip : clips) {
    Rect r2 = autoCropOfBWImage(bw.clip(clip));
    l.add(translateRect(r2, clip.x, clip.y));
  }
  ret l;
}