static BWImage decolorizeImage(Decolorizer decolorizer, BufferedImage image) {
  if (image == null) null;
  var gp = grabbableIntPixels_fastOrSlow(image);
  if (gp == null) null;
  
  var ping = pingSource();
  int[] image = gp.data;
  int w = gp.w, h = gp.h;
  int scanlineExtra = gp.scanlineStride-w;
  int iImage = gp.offset, i = 0;
  byte[] image2 = new[w*h];
  
  for y to h: {
    for x to w: {
      int packed = image[iImage++];
      int brightness = decolorizer.toGrayScale(packed);
      image2[i++] = (byte) brightness;
    }

    iImage += scanlineExtra;
    ping?!;
  }
  
  ret BWImage(w, h, image2);
}