static RGBImage rgbImageFromLLLDouble255(L<LL<Double>> l) {
  int h = l(l), w = l(first(l));
  RGBImage img = new(w, h);
  for y to h:
    for x to w: {
      L<Double> pix = l.get(y).get(x);
      img.setRGB(x, y, (int) pix.get(0), (int) pix.get(1), (int) pix.get(2));
}