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 }