static L<Pt> pixelsByBrightness(IBWImage image) {
  float[] data = image.toFloatArray();
  int n = l(data);
  int[] indices = new[n];
  for i to n: indices[i] = i;
  timSortIntArrayWithComparator(indices, (i, j) -> cmp(data[i], data[j]));
  int w = image.w();
  ret listFromFunction(n, i -> ptFromPixelIndex(indices[i], w));
}