001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.image.processing.edges;
031
032import org.openimaj.image.FImage;
033import org.openimaj.image.combiner.ImageCombiner;
034
035/**
036 * Non-maximum suppression using magnitude and orientation images.
037 * 
038 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
039 */
040public class NonMaximumSuppression implements ImageCombiner<FImage, FImage, FImage> {
041        /**
042         * Perform non-maximum suppression.
043         * 
044         * @param mag Gradient magnitudes
045         * @param ori Gradient orientations
046         * @return non-maximum suppressed magnitude image.
047         */
048        public static FImage computeSuppressed(FImage mag, FImage ori) {
049                int height = mag.getHeight(), width = mag.getWidth();
050        
051                FImage suppressed = new FImage(width, height);
052
053                float p8 = (float) (Math.PI / 8.0);
054                
055                //Compute max suppresion        
056                for (int y=1; y<height-1; y++) {
057                        for (int x=1; x<width-1; x++) {
058                                if (mag.pixels[y][x] > 0) {
059                                        float t = (float) (ori.pixels[y][x] - Math.PI/2);   //angle of edge in -pi to pi
060                                        
061                                        if ((t>=-p8 && t<=p8) || (t<=-7*p8 || t>=7*p8)) { //zero degrees or 180 degrees
062                                                if (mag.pixels[y][x] > mag.pixels[y+1][x] && mag.pixels[y][x] >= mag.pixels[y-1][x]) {
063                                                        suppressed.pixels[y][x] = mag.pixels[y][x];
064                                                }
065                                        } else if ((t>=3*p8 && t<=5*p8) || (t>=-5*p8 && t<=-3*p8)) { //+/-90 degrees
066                                                if (mag.pixels[y][x] >= mag.pixels[y][x+1] && mag.pixels[y][x] > mag.pixels[y][x-1]) {
067                                                        suppressed.pixels[y][x] = mag.pixels[y][x];
068                                                }
069                                        } else if ((t>=p8 && t<=3*p8) || (t>=-7*p8 && t<=-5*p8)) { //+45 degrees or -135 degrees
070                                                if (mag.pixels[y][x] > mag.pixels[y+1][x-1] && mag.pixels[y][x] >= mag.pixels[y-1][x+1]) {
071                                                        suppressed.pixels[y][x] = mag.pixels[y][x];
072                                                }
073                                        } else {
074                                                if (mag.pixels[y][x] > mag.pixels[y-1][x-1] && mag.pixels[y][x] >= mag.pixels[y+1][x+1]) {
075                                                        suppressed.pixels[y][x] = mag.pixels[y][x];
076                                                }
077                                        }
078                                }
079                        }
080                }
081                
082                return suppressed;
083        }
084
085        /**
086         * Perform non-maximum suppression.
087         * 
088         * @param mag Gradient magnitudes
089         * @param ori Gradient orientations
090         * @return non-maximum suppressed magnitude image.
091         * 
092         * @see org.openimaj.image.combiner.ImageCombiner#combine(org.openimaj.image.Image, org.openimaj.image.Image)
093         */
094        @Override
095        public FImage combine(FImage mag, FImage ori) {
096                return computeSuppressed(mag, ori);
097        }
098}