/**
 * Copyright (c) 2011, The University of Southampton and the individual contributors.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 *   *  Redistributions of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 *
 *   *  Redistributions in binary form must reproduce the above copyright notice,
 *      this list of conditions and the following disclaimer in the documentation
 *      and/or other materials provided with the distribution.
 *
 *   *  Neither the name of the University of Southampton nor the names of its
 *      contributors may be used to endorse or promote products derived from this
 *      software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.openimaj.image.processing.edges;

import org.openimaj.image.FImage;
import org.openimaj.image.combiner.ImageCombiner;

/**
 * Non-maximum suppression using X and Y gradient images.
 * 
 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
 */
public class NonMaximumSuppressionTangent implements ImageCombiner<FImage, FImage, FImage> {

        /**
         * Perform non-maximum suppression.
         * 
         * @param dxImage
         *            x-gradients
         * @param dyImage
         *            y-gradients
         * @return non-maximum suppressed magnitude image.
         */
        public static FImage computeSuppressed(FImage dxImage, FImage dyImage) {
                return computeSuppressed(dxImage, dyImage, null);
        }

        /**
         * Perform non-maximum suppression.
         * 
         * @param dxImage
         *            x-gradients
         * @param dyImage
         *            y-gradients
         * @param magsOut
         *            an image with the same dimensions as dxImage and dyImage for
         *            holding the magnitudes before non-maximum suppression. May be
         *            <code>null</code>.
         * @return non-maximum suppressed magnitude image.
         */
        public static FImage computeSuppressed(FImage dxImage, FImage dyImage, FImage magsOut) {
                final float[][] diffx = dxImage.pixels;
                final float[][] diffy = dyImage.pixels;
                final int width = dxImage.width;
                final int height = dxImage.height;

                final float[][] mag = magsOut == null ? new float[height][width] : magsOut.pixels;

                for (int y = 0; y < height; y++)
                        for (int x = 0; x < width; x++)
                                mag[y][x] = (float) Math.sqrt(diffx[y][x] * diffx[y][x] + diffy[y][x] * diffy[y][x]);

                final FImage outimg = new FImage(width, height);
                final float[][] output = outimg.pixels;

                for (int y = 1; y < height - 1; y++) {
                        for (int x = 1; x < width - 1; x++) {
                                int dx, dy;

                                if (diffx[y][x] > 0)
                                        dx = 1;
                                else
                                        dx = -1;

                                if (diffy[y][x] > 0)
                                        dy = -1;
                                else
                                        dy = 1;

                                float a1, a2, b1, b2, A, B, point, val;
                                if (Math.abs(diffx[y][x]) > Math.abs(diffy[y][x]))
                                {
                                        a1 = mag[y][x + dx];
                                        a2 = mag[y - dy][x + dx];
                                        b1 = mag[y][x - dx];
                                        b2 = mag[y + dy][x - dx];
                                        A = (Math.abs(diffx[y][x]) - Math.abs(diffy[y][x])) * a1 + Math.abs(diffy[y][x]) * a2;
                                        B = (Math.abs(diffx[y][x]) - Math.abs(diffy[y][x])) * b1 + Math.abs(diffy[y][x]) * b2;
                                        point = mag[y][x] * Math.abs(diffx[y][x]);
                                        if (point >= A && point > B) {
                                                val = Math.abs(diffx[y][x]);
                                                output[y][x] = val;
                                        }
                                        else {
                                                val = 0;
                                                output[y][x] = val;
                                        }
                                }
                                else
                                {
                                        a1 = mag[y - dy][x];
                                        a2 = mag[y - dy][x + dx];
                                        b1 = mag[y + dy][x];
                                        b2 = mag[y + dy][x - dx];
                                        A = (Math.abs(diffy[y][x]) - Math.abs(diffx[y][x])) * a1 + Math.abs(diffx[y][x]) * a2;
                                        B = (Math.abs(diffy[y][x]) - Math.abs(diffx[y][x])) * b1 + Math.abs(diffx[y][x]) * b2;
                                        point = mag[y][x] * Math.abs(diffy[y][x]);
                                        if (point >= A && point > B) {
                                                val = Math.abs(diffy[y][x]);
                                                output[y][x] = val;
                                        }
                                        else {
                                                val = 0;
                                                output[y][x] = val;
                                        }
                                }
                        }
                }

                return outimg;
        }

        /**
         * Perform non-maximum suppression.
         * 
         * @param dxImage
         *            x-gradients
         * @param dyImage
         *            y-gradients
         * @return non-maximum suppressed magnitude image.
         * 
         * @see org.openimaj.image.combiner.ImageCombiner#combine(org.openimaj.image.Image,
         *      org.openimaj.image.Image)
         */
        @Override
        public FImage combine(FImage dxImage, FImage dyImage) {
                return computeSuppressed(dxImage, dyImage);
        }
}