code: private void sort(FastQueue<BrightFeature> input ,
  					  FastQueue<Helper> pos , FastQueue<Helper> neg ) {
  		pos.reset();
  		neg.reset();
  
  		for( int i = 0; i < input.size; i++ ) {
  			BrightFeature f = input.get(i);
  			if( f.white) {
  				pos.grow().wrap(f,i);
  			} else {
  				neg.grow().wrap(f,i);
  			}
  		}
  	}
docs: Splits the set of input features into positive and negative laplacian lists.
  Keep track of the feature's index in the original input list.  This is
  the index that needs to be returned.