// same brightness level count for each channel for now
srecord noeq PosterizeBufferedImage(int brightnessLevels, BufferedImage img) is PixelPreservingImageOpResult<BufferedImage> {
  BufferedImage result;
  
  run {
    if (brightnessLevels >= 256 || img == null) ret with result = img;
    
    GrabbableIntPixels gp = grabbableIntPixels_fastOrSlow(img);
    int w = img.getWidth(), h = img.getHeight(), n = w*h;
    int[] pixels = gp.data;
    int[] pixels2 = new[n];
    var posterizer = cachePosterizer(SinglePixelPosterizer(brightnessLevels));

    int iOut = 0, iIn = gp.offset;
    for y to h: {
      for x to w: {
        int rgb = pixels[iIn+x];
        pixels2[iOut++] = rgbInt(
          posterizer.get(rgbRed(rgb)),
          posterizer.get(rgbGreen(rgb)),
          posterizer.get(rgbBlue(rgb)));
      }
      iIn += gp.scanlineStride;
    }
  
    result = bufferedImageWithoutAlpha(w, h, pixels2);
  }
  
  public BufferedImage pixelPreservingSrcImage() { ret img; }
  
  BufferedImage get() { if (result == null) run(); ret result; }
}