code: private static double calculateSaturationHsl(double chroma, double lightness) {
  
      double d = 1 - Math.abs(2 * lightness - 1);
      if (d == 0) {
        return 0;
      }
      return chroma / d;
    }
docs: Calculate the {@link Saturation} for {@link ColorModel#HSL}.
  
  @param chroma is the {@link Chroma} value.
  @param lightness is the {@link Lightness} value.
  @return the {@link Saturation}.