static BWIntegralImage bwIntegralImage(BufferedImage img, Decolorizer decolorizer default null) {
  ret img == null ? null : new BWIntegralImage(img, decolorizer);
}

meta-for BWImage also as IBWImage {
  static BWIntegralImage bwIntegralImage(BWImage img) {
    ret img == null ? null : new BWIntegralImage(img);
  }
}