meta-for IBWIntegralImage in IBWIntegralImage, BWIntegralImage {

  // clip is in output coordinates

  static BufferedImage scaledGrayImageFromBWIntegralImage_clip(IBWIntegralImage img, double scalingFactor, Rect clip) {

    int w = clip.w, h = clip.h;

    int w1 = img.getWidth(), h1 = img.getHeight();

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

    int i = 0;

    int xx2 = clip.x2(), yy2 = clip.y2();

    for (int y = clip.y; y < yy2; y++)

      for (int x = clip.x; x < xx2; x++) {

        // TODO: optimize

        double x1 = x/scalingFactor, x2 = (x+1)/scalingFactor;

        double y1 = y/scalingFactor, y2 = (y+1)/scalingFactor;

        int pixel = iround(img.getPixelAverage(x1, y1, x2, y2));

        pixels[i++] = clampToUByte(pixel);

      }

    ret newGrayBufferedImage(w, h, pixels);

  }

}