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
        int x1 = ifloor(x/scalingFactor), x2 = ifloor(max(x1+1, (x+1)/scalingFactor));
        int y1 = ifloor(y/scalingFactor), y2 = ifloor(max(y1+1, (y+1)/scalingFactor));
        int pixel = iround(img.getPixelAverage(x1, y1, x2, y2));
        pixels[i++] = clampToUByte(pixel);
      }
    ret newGrayBufferedImage(w, h, pixels);
  }
  
}