// same brightness level count for each channel for now
sclass PosterizeBufferedImageToHi15 {
  BufferedImage img;
  Hi15Image result;
  IPosterizer posterizer;

  *(int brightnessLevels, BufferedImage *img) {
    if (brightnessLevels >= 256 || img == null)
      posterizer = new DummyPosterizer;
    posterizer = SinglePixelPosterizer(brightnessLevels);
  }
  
  *(IPosterizer *posterizer, BufferedImage *img) {}
  
  run {
    if (img == null) ret;
    if (posterizer cast DummyPosterizer)
      ret with result = new Hi15Image(img);
    
    GrabbableRGBBytePixels gp = grabbableRGBBytePixels(img);
    if (gp != null)
      ret with run(gp);
      
    GrabbableIntPixels gp2 = grabbableIntPixels_fastOrSlow(img);
    run(gp2);
  }
  
  void run(GrabbableIntPixels gp) {
    int w = img.getWidth(), h = img.getHeight(), n = w*h;
    int[] pixels = gp.data;
    short[] pixels2 = new[n];
    byte[] cache = cachePosterizer();
    int extraStride = gp.scanlineStride-w;

    int iOut = 0, iIn = gp.offset;
    for y to h: {
      for x to w: {
        int rgb = pixels[iIn++];
        pixels2[iOut++] = (short)
          ((cache[(rgb >> 16) & 0xFF] << 10) |
          (cache[(rgb >> 8) & 0xFF] << 5) |
          cache[rgb & 0xFF]);
      }
      iIn += extraStride;
    }
  
    result = new Hi15Image(w, h, pixels2);
  }
  
  void run(GrabbableRGBBytePixels gp) {
    int w = img.getWidth(), h = img.getHeight(), n = w*h;
    byte[] pixels = gp.data;
    short[] pixels2 = new[n];
    byte[] cache = cachePosterizer();
    int extraStride = gp.scanlineStride-w*3;

    int iOut = 0, iIn = gp.offset;
    for y to h: {
      for x to w: {
        int r = pixels[iIn++] & 0xFF;
        int g = pixels[iIn++] & 0xFF;
        int b = pixels[iIn++] & 0xFF;
        pixels2[iOut++] = (short)
          ((cache[r] << 10) |
          (cache[g] << 5) |
          cache[b]);
      }
      iIn += extraStride;
    }
  
    result = new Hi15Image(w, h, pixels2);
  }
  
  public BufferedImage pixelPreservingSrcImage() { ret img; }
  
  Hi15Image get() { if (result == null) run(); ret result; }
  
  byte[] cachePosterizer() {
    byte[] cache = new[256];
    for i to 256:
      cache[i] = (byte) (posterizer.get(i) >> 3);
    ret cache;
  }
}

Began life as a copy of #1035253