static Image2B iBinaryImageToImage2B(IBinaryImage img) {
  if (img == null) null;
  if (img cast Image2B) ret img;
  int w = img.getWidth(), h = img.getHeight();
  byte[] pixels = new[(w*h+7)/8];
  int i = 0;
  for y to h:
    for x to w: {
      if (img.getBoolPixel(x, y))
        pixels[i/8] |= 1 << (i & 7);
      i++;
    }
    
  ret new Image2B(w, h, pixels);
}