srecord noeq PosterizeBWImage(int brightnessLevels, BWImage img) is PixelPreservingImageOpResult<BWImage> {

  BWImage result;

  run {

    if (brightnessLevels >= 256 || img == null) ret with result = img;

    byte[] pixels = img.getBytes();

    int w = img.getWidth(), h = img.getHeight(), n = pixels.length;

    byte[] pixels2 = new[n];

    var posterizer = cachePosterizer(SinglePixelPosterizer(brightnessLevels));

    for i to n:

      pixels2[i] = (byte) posterizer.get(ubyteToInt(pixels[i]));

    result = new BWImage(w, h, pixels2);

  }

  public BWImage pixelPreservingSrcImage() { ret img; }

  BWImage get() { if (result == null) run(); ret result; }

}