static RGBImage rgb111(RGBImage rgb) {
  int w = rgb.width, h = rgb.height;
  RGBImage img = new(w, h);
  for y to h:
    for x to w:
      img.setPixel(x, y, rgbPixelTo111(rgb.getInt(x, y)));
  ret img;
}

static RGBImage rgb111(BufferedImage img) {
  ret rgb111(new RGBImage(img));
}