meta-for IIntegralImage in IIntegralImage, IntegralImage {
  static double ii_averageBrightnessOfArea(IIntegralImage img, int x1, int y1, int x2, int y2) {
    ret doubleRatio(img.rectSum(x1, y1, x2, y2), (x2-x1)*(y2-y1)*3);
  }
  
  static double ii_averageBrightnessOfArea(IIntegralImage img, int x1, int y1, int x2, int y2, int channel) {
    ret doubleRatio(img.rectSum(x1, y1, x2, y2, channel), (x2-x1)*(y2-y1));
  }
  
  static double ii_averageBrightnessOfArea(IIntegralImage img, Rect r) {
    ret ii_averageBrightnessOfArea(img, r.x, r.y, r.x2(), r.y2());
  }
  
  static double ii_averageBrightnessOfArea(IIntegralImage img, Rect r, int channel) {
    ret ii_averageBrightnessOfArea(img, r.x, r.y, r.x2(), r.y2(), channel);
  }
}