static BWImage transformBufferedImageToBWImage(IF1<Int, Float> f, BufferedImage img) {
  if (img == null) null;
  int w = img.getWidth(), h = img.getHeight();
  BWImage img2 = new(w, h);
  for y to h: for x to w:
    img2.setPixel(x, y, f.get(img.getRGB(x, y)));
  ret img2;
}