001/*******************************************************************************
002 * This software is provided as a supplement to the authors' textbooks on digital
003 * image processing published by Springer-Verlag in various languages and editions.
004 * Permission to use and distribute this software is granted under the BSD 2-Clause
005 * "Simplified" License (see http://opensource.org/licenses/BSD-2-Clause).
006 * Copyright (c) 2006-2023 Wilhelm Burger, Mark J. Burge. All rights reserved.
007 * Visit https://imagingbook.com for additional details.
008 ******************************************************************************/
009package Ch03_Point_Operations;
010
011import ij.ImagePlus;
012import ij.plugin.filter.PlugInFilter;
013import ij.process.ImageProcessor;
014import imagingbook.common.ij.DialogUtils;
015import imagingbook.core.jdoc.JavaDocHelp;
016import imagingbook.sampleimages.GeneralSampleImage;
017
018import static imagingbook.common.ij.IjUtils.noCurrentImage;
019
020/**
021 * <p>
022 * This ImageJ plugin performs linear histogram equalization on the selected grayscale image, which is modified. See
023 * Sec. 3.5 (Prog. 3.2) of [1] for additional details.
024 * </p>
025 * <p>
026 * [1] W. Burger, M.J. Burge, <em>Digital Image Processing &ndash; An Algorithmic Introduction</em>, 3rd ed, Springer
027 * (2022).
028 * </p>
029 *
030 * @author WB
031 */
032public class Equalize_Histogram implements PlugInFilter, JavaDocHelp {
033
034        /** Constructor, asks to open a predefined sample image if no other image is currently open. */
035        public Equalize_Histogram() {
036                if (noCurrentImage()) {
037                        DialogUtils.askForSampleImage(GeneralSampleImage.IrishManor);
038                }
039        }
040
041        @Override
042        public int setup(String arg, ImagePlus im) {
043                return DOES_8G;
044        }
045    
046        @Override
047        public void run(ImageProcessor ip) {
048                int M = ip.getWidth();
049                int N = ip.getHeight();
050                int K = 256; // number of intensity values
051
052                int[] H = ip.getHistogram();
053                // compute the cumulative histogram H (recursively and in-place):
054                for (int j = 1; j < H.length; j++) {
055                        H[j] = H[j - 1] + H[j];
056                }
057
058                // equalize the image:
059                for (int v = 0; v < N; v++) {
060                        for (int u = 0; u < M; u++) {
061                                int a = ip.get(u, v);
062                                int b = H[a] * (K - 1) / (M * N);
063                                ip.set(u, v, b);
064                        }
065                }
066        }
067        
068}