meta-for IIntegralImage in IIntegralImage, IntegralImage {
  // one channel
  static int integralImage_sumRect(IIntegralImage img, int x1, int y1, int x2, int y2, int channel) {
    ret iround(img.rectSum(x1, y1, x2, y2, channel));
  }
  
  // sum all channels. TODO: might exceed int range on huge images
  static int integralImage_sumRect(IIntegralImage img, int x1, int y1, int x2, int y2) {
    ret iround(img.rectSum(x1, y1, x2, y2));
  }
}