static double averageSaturation(BufferedImage img) {
  if (img == null) ret 0;
  int w = img.getWidth(), h = img.getHeight();
  double sum = 0;
  for y to h: for x to w:
    sum += saturationFromRGB(img.getRGB(x, y));
  ret doubleRatio(sum, w*h);
}

Began life as a copy of #1020181