static BWIntegralImage blendBWIntegralImages(Cl<? extends IIntegralImage> images) {

  if (empty(images)) null;

  var img1 = first(images);

  int nImages = l(images);

  int w = img1.getWidth(), h = img1.getHeight(), n = w*h;

  double[] pixels = new[w*h];

  for (var img : images) {

    int i = 0;

    for y to h:

      for x to w:

        pixels[i++] += img.getPixel(x, y, 0);

  }

  byte[] bytes = new[n];

  double inv = 1.0/nImages;

  for i to n: bytes[i] = clampToUByte(iround(pixels[i]*inv));

  ret new BWIntegralImage(BWImage(w, h, bytes));

}