// Another minor generalization over Haar features allowing multiple
// black and white areas at the same time

// (It's only actually different from combining multiple Haar features
// when l(rBlack) != l(rWhite).)
//
// Result classification, as always:
//
//   positive = match
//   0        = non-match  (indifferent/not applicable)
//   negative = anti-match (inverted Haar feature found)

srecord MultiHaar(IIntegralImage img, L<DoubleRect> rBlack, L<DoubleRect> rWhite) {
  double get() {
    double blackArea = totalAreaOfDoubleRects(rBlack);
    double whiteArea = totalAreaOfDoubleRects(rWhite);

    double whiteSum = 0, blackSum = 0;
    for (DoubleRect r : rWhite) whiteSum += img.pixelSum(r);
    for (DoubleRect r : rBlack) blackSum += img.pixelSum(r);

    ret (doubleRatio(whiteSum, whiteArea) - doubleRatio(blackSum, blackArea))/255.0;
  }
}