compare method
Calculates histogram similarity using standard intersection
Implementation
@override
double compare(Image src1, Image src2) {
// Delegates histogram initialization to parent
super.compare(src1, src2);
var sum = 0.0;
var alphaBit = (ignoreAlpha) ? 0 : 1;
sum += _diff(_histograms._first.redHist, _histograms._second.redHist) +
_diff(_histograms._first.greenHist, _histograms._second.greenHist) +
_diff(_histograms._first.blueHist, _histograms._second.blueHist) +
(alphaBit * _diff(_histograms._first.alphaHist, _histograms._second.alphaHist));
return 1 - (sum / (3 + alphaBit));
}