code: public ImageScale lookup( double sigma ) {
  		ImageScale best = null;
  		double bestValue = Double.MAX_VALUE;
  
  		for (int i = 0; i < usedScales.size(); i++) {
  			ImageScale image = usedScales.get(i);
  			double difference = Math.abs(sigma-image.sigma);
  			if( difference < bestValue ) {
  				bestValue = difference;
  				best = image;
  			}
  		}
  		return best;
  	}
docs: Looks up the image which is closest specified sigma