static L<Int> pixelColorsWithNonZeroSaturation(BufferedImage img) {
  if (img == null) null;
  int w = img.getWidth(), h = img.getHeight();
  new L<Int> out;
  int rgb;
  for y to h: for x to w:
    if (saturationFromRGB(rgb = img.getRGB(x, y)) != 0)
      out.add(rgb);
  ret out;
}