sclass IntegratedBWImage > HashedBWImage is MakesIBWIntegralImage {
  IBWIntegralImage ii;

  *(BWImage image) { super(image); }
  
  public getIBWIntegralImage() {
    while (ii == null) synchronized {
      if (ii == null)
        ii = bwIntegralImage(image);
    }
    ret ii;
  }
}