Extract Local Interest Points from a spectrogram

Audio Interest Point

package processing.signals;

import java.util.ArrayList;

/**
 * Extract all local features from current spectrogram
 * 
 * @author Daniel Kohlsdorf
 */
public class LocalFeatureExtractor {	

	public ArrayList<LocalFeature> keypoints(ArrayList<double[]> spec, int offset, int r, double th) {
		ArrayList<LocalFeature> points = new ArrayList<LocalFeature>();
		int T = spec.size();
		for (int t = r; t < T - r; t+= 2) {
			for (int f = Math.max(r, 0); f < spec.get(t).length - r; f++) {
				double sumNeighborhoodT = 0;
				double sumNeighborhoodF = 0;
				double maxT = 0;
				for (int d = t - r; d < t + r; d++) {
					sumNeighborhoodT += spec.get(t)[f];
					if(spec.get(d)[f] > maxT) {
						maxT = spec.get(d)[f];
					}
				}
				
				double maxF = 0;
				for (int d = f - r; d < f + r; d++) {
					sumNeighborhoodF += spec.get(t)[d];
					if(spec.get(t)[d] > maxT) {
						maxF = spec.get(t)[d];
					}
				}
				double noise = (1.0 / (2 * r)) * Math.min(sumNeighborhoodT, sumNeighborhoodF);
				if (spec.get(t)[f] > Math.max(maxT, maxF) || spec.get(t)[f] > noise + th) {
					points.add(new LocalFeature(t + offset, f));
				} 
			}
		}

		return points;
	}

}