static IIntegralImage compressBWIntegralImage(IIntegralImage img) {
  int w = img.getWidth(), h = img.getHeight();
  
  if (w >= 2) {
    IIHorizontalSplit split = new(img);
    var a2 = toIISingleColorIfPossible(split.a());
    var b2 = toIISingleColorIfPossible(split.b());
    if (a != a2 || b == b2)
      img = split;
  }
  
  ret img;
    if (iiIsSingleColor(split.a()))
      split.setA(IISingleColor(uRoot(split.a()).color()));
    var img1 = IIVirtualClip(img, 0, 0, mid, h);
    var img2 = IIVirtualClip(img, mid, 0, w-mid, h);
  }
}