static int colorCount332(BufferedImage img) {
  ret colorCount332(RGBImage(img));
}

static int colorCount332(RGBImage img) {
  int w = img.w(), h = img.h();
  new BitSet bs;
  for y to h: for x to w:
    setBit(bs, to332(img.getInt(x, y)));
  ret bitCount(bs);
}