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.image.processing.algorithm;
31
32 import org.openimaj.image.FImage;
33 import org.openimaj.image.processor.ImageProcessor;
34 import org.openimaj.image.processor.SinglebandImageProcessor;
35
36 /**
37 * An {@link ImageProcessor} that performs histogram equalisation (projecting
38 * the colours back into the image).
39 *
40 * @author David Dupplaw (dpd@ecs.soton.ac.uk)
41 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
42 *
43 * @created 31 Mar 2011
44 */
45 public class EqualisationProcessor implements SinglebandImageProcessor<Float, FImage> {
46 /**
47 * Equalise the colours in the image. Creates a histogram that contains as
48 * many bins as colours, equalises it, then back-projects it into an image.
49 * The resulting image has equalised values between 0 and 1. It assumes the
50 * image has already been normalised such that its values are also between 0
51 * and 1.
52 *
53 * It is assumed that there are 256 discrete grey-levels.
54 *
55 * @see "http://www.generation5.org/content/2004/histogramEqualization.asp"
56 */
57 @Override
58 public void processImage(FImage image) {
59 // This will be a histogram of all intensities
60 final int[] hg = new int[256];
61
62 // Create the histogram
63 for (int r = 0; r < image.height; r++) {
64 for (int c = 0; c < image.width; c++) {
65 final int i = Math.round(255 * image.pixels[r][c]);
66 hg[i]++;
67 }
68 }
69
70 // Create cumulative histogram
71 for (int i = 1; i < 256; i++) {
72 hg[i] += hg[i - 1];
73 }
74
75 // The assumption is that the max value will be 1
76 final float alpha = 255f / (image.getWidth() * image.getHeight());
77
78 // Back-project into the new image
79 for (int r = 0; r < image.height; r++) {
80 for (int c = 0; c < image.width; c++) {
81 final int i = Math.round(255 * image.pixels[r][c]);
82 image.pixels[r][c] = Math.round(hg[i] * alpha) / 255.0f;
83 }
84 }
85 }
86 }