1 /** 2 * Copyright (c) 2011, The University of Southampton and the individual contributors. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without modification, 6 * are permitted provided that the following conditions are met: 7 * 8 * * Redistributions of source code must retain the above copyright notice, 9 * this list of conditions and the following disclaimer. 10 * 11 * * Redistributions in binary form must reproduce the above copyright notice, 12 * this list of conditions and the following disclaimer in the documentation 13 * and/or other materials provided with the distribution. 14 * 15 * * Neither the name of the University of Southampton nor the names of its 16 * contributors may be used to endorse or promote products derived from this 17 * software without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 21 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 22 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR 23 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 24 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 25 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON 26 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 28 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 */ 30 package org.openimaj.video.processing.pixels; 31 32 import org.openimaj.image.FImage; 33 import org.openimaj.video.analyser.VideoAnalyser; 34 import org.openimaj.video.processing.shotdetector.HistogramVideoShotDetector; 35 36 /** 37 * Compute the mean and variance fields from a video of {@link FImage} frames. 38 * The generated fields could be used to analyse which parts of a video are 39 * stationary or change a lot. If your video consists of multiple shots, between 40 * which there are large changes in the content, then it probably makes sense to 41 * segment the video using a {@link HistogramVideoShotDetector} and apply a new 42 * analyser to each shot independently. 43 * 44 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk) 45 */ 46 public class FMeanVarianceField 47 extends 48 VideoAnalyser<FImage> 49 { 50 private FImage mean; 51 private FImage m2; 52 private int n; 53 54 @Override 55 public void analyseFrame(FImage frame) { 56 final int width = frame.width; 57 final int height = frame.height; 58 59 if (mean == null || mean.width != width || mean.height != height) { 60 n = 0; 61 mean = new FImage(width, height); 62 m2 = new FImage(width, height); 63 } 64 65 final float[][] mp = mean.pixels; 66 final float[][] m2p = m2.pixels; 67 final float[][] fp = frame.pixels; 68 for (int y = 0; y < height; y++) { 69 for (int x = 0; x < width; x++) { 70 final float v = fp[y][x]; 71 final float delta = v - mp[y][x]; 72 73 n++; 74 mp[y][x] = mp[y][x] + delta / n; 75 m2p[y][x] = m2p[y][x] + delta * (v - mp[y][x]); 76 } 77 } 78 } 79 80 /** 81 * Reset the accumulated field data. 82 * 83 * @see org.openimaj.video.processor.VideoProcessor#reset() 84 */ 85 @Override 86 public void reset() { 87 this.mean = null; 88 this.m2 = null; 89 } 90 91 /** 92 * Get the mean field of all the frames that have been analysed so far. 93 * 94 * @return the mean field. 95 */ 96 public FImage getMean() { 97 return mean; 98 } 99 100 /** 101 * Get the variance field of all the frames that have been analysed so far. 102 * 103 * @return the variance field. 104 */ 105 public FImage getVariance() { 106 if (m2 == null) 107 return null; 108 109 return m2.divide((float) (n - 1)); 110 } 111 }