static BufferedImage scaledGrayImageFromBWIntegralImage(int w, BWIntegralImage img) {
  ret scaledGrayImageFromBWIntegralImage(img, w);
}

static BufferedImage scaledGrayImageFromBWIntegralImage(BWIntegralImage img, int w, int h default heightForWidth(img.w, img.h, w)) {
  int w1 = img.w, h1 = img.h;
  byte[] pixels = new[w*h];
  int i = 0;
  for y to h:
    for x to w: {
      // TODO: optimize
      int x1 = x*w1/w, x2 = max(x1+1, (x+1)*w1/w);
      int y1 = y*h1/h, y2 = max(y1+1, (y+1)*h1/h);
      int pixel = iround(img.getPixelAverage(x1, y1, x2, y2));
      pixels[i++] = clampToUByte(pixel;
    }
  ret newGrayBufferedImage(w, h, pixels);
}