public boolean detect(byte[] data, int width, int height) {
 
 		// half width and height to reduce loops
		int half_height = height / 2;
		int half_width = width / 2;
 
		// boolean map to hold our threshold pic
		boolean[] map = new boolean[half_height * half_width];
		for (int y = 0, i = 0, ii = 0; y < half_height; y++) {
			for (int x = 0; x < half_width; x++, i+=2,ii++) {
				int l = (0xff & ((int) data[i])) - 16;
				if (previous_frame != null) {
					int pl = (0xff & ((int) previous_frame[i])) - 16;
					int d = pl;
					// merge 50% of each frame, lets not use division
					d = ((int)((5 * l) + (5 * d))-(d*10));
					// if theres a negative diff, lets reverse it
					if (d < 0){
						d = -d;
					}
					//build up our threshold map
					map[ii] = d > 150;
				}
			}
		}
		previous_frame = data;
		boolean erode = false;
		for (int y = 0, i = 0; y < half_height; y++) {
			for (int x = 0; x < half_width; x++, i++) {
				erode = false;
				if (map[i]) {
					loop through the pixels around it
					for (int yi=-2;yi<=2;yi++){
						for (int xi=-2;xi<=2;xi++){
							int px = (y+yi) * half_width + (x+xi);
							if (px >= 0 && px < map.length) {
								// if a pixel is eroded, carry on
								if (!map[px]) {
									erode = true;
									break;
								}
							}
						}
					}
					// if no pixels around this pixel have been eroded, we know there's probably some motion
					if (!erode) {
						return true;
					}
				}
			}
		}
		return false;
	}