static L<Pt> listOfBrightestPixels(BWImage img) {
  int w = img.getWidth(), h = img.getHeight();
  new LPair<Pt, Int> l;
  for y to h:
    for x to w:
      l.add(pair(pt(x, y), img.getInt(x, y));
  ret sortBySecondOfPairsDesc_inPlace(l);
}