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 static java.lang.Math.atan;
033import static java.lang.Math.sqrt;
034
035import org.openimaj.image.FImage;
036import org.openimaj.image.analyser.ImageAnalyser;
037
038/**
039 * Using a simple sobel-like x and y derivative kernel, find edges in an image.
040 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
041 * @author Sina Samangooei (ss@ecs.soton.ac.uk)
042 *
043 */
044public class EdgeFinder implements ImageAnalyser<FImage> {
045        protected float [][] kx;
046        protected float [][] ky;
047
048        /**
049         * The magnitudes of each edge as worked out by the hypotenuse of the triangle formed by the dx and dy of a pixel
050         */
051        public FImage magnitude;
052        /**
053         * The direction of each edge as worked out by the angle between the triangle formed by the dx and dy of a pixel
054         */
055        public FImage angle;
056
057        /**
058         * Find edges in an image using the following edge kernels
059         * @param kx
060         * @param ky
061         */
062        public EdgeFinder(float [][] kx, float [][] ky) {
063                this.kx = kx;
064                this.ky = ky;
065        }
066
067        /**
068         * Find the edges in an image using default, sobel like 5x5 derivative kernels
069         */
070        public EdgeFinder() {
071                kx = new float[][] {
072                                {+1, +1, 0, -1, -1},
073                                {+2, +2, 0, -2, -2},
074                                {+2, +2, 0, -2, -2},
075                                {+2, +2, 0, -2, -2},
076                                {+1, +1, 0, -1, -1}
077                };
078
079                ky = new float[][] {
080                                {+1, +2, +2, +2, +1},
081                                {+1, +2, +2, +2, +1},
082                                { 0,  0,  0,  0,  0},
083                                {-1, -2, -2, -2, -1},
084                                {-1, -2, -2, -2, -1}
085                };
086        }
087
088        /* (non-Javadoc)
089         * @see org.openimaj.image.processor.ImageProcessor#processImage(org.openimaj.image.Image)
090         */
091        @Override
092        public void analyseImage(FImage image) {
093                int height = image.getHeight();
094                int width = image.getWidth();
095
096                magnitude = new FImage(width, height);
097                angle = new FImage(width, height);
098
099                int w = (kx.length - 1) / 2;
100
101                for (int y=w+1; y<height-w; y++) {
102                        for (int x=w+1; x<width-w; x++) {
103                                //compute gradient
104                                double gx = 0;
105                                double gy = 0;
106                                for (int j=0; j<kx.length; j++) {
107                                        for (int i=0; i<kx.length; i++) {
108                                                gx += image.pixels[y-w+j][x-w+i] * kx[j][i];
109                                                gy += image.pixels[y-w+j][x-w+i] * ky[j][i];
110                                        }
111                                }
112
113                                magnitude.pixels[y][x] = (float) sqrt(gx*gx + gy*gy);
114
115                                if(gy!=0)
116                                        angle.pixels[y][x] = (float) atan(gx/-gy);
117                                else
118                                        angle.pixels[y][x] = 1.57f;
119                        }
120                }
121        }       
122}