static BWImage bwAutoContrastAllRects(BWImage bw, L<Rect> rects, float def) {
  int w = bw.getWidth(), h = bw.getHeight();
  BWImage bw2 = new BWImage(bw);
  for (Rect r : rects) {
    BWImage c = bwAutoContrast(bw.clip(r), def);
    copyBWImage(c, 0, 0, bw2, r.x, r.y, r.w, r.h);
  }
  ret bw2;
}