/**
 * 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.algorithm;

import java.util.Set;

import org.openimaj.image.FImage;
import org.openimaj.image.pixel.Pixel;
import org.openimaj.image.processor.SinglebandImageProcessor;

/**
 * Min filter; replaces each pixel with the minimum of its neighbours. This is
 * equivalent to greyscale morphological erosion.
 * 
 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
 * 
 */
public class MinFilter implements SinglebandImageProcessor<Float, FImage> {
        private Set<Pixel> support;
        private int blockWidth;
        private int blockHeight;

        /**
         * Construct with the given support region for selecting pixels to take the
         * median from. The support mask is a set of <code>n</code> relative x, y
         * offsets from the pixel currently being processed, and can be created
         * using the methods or constants in the {@link FilterSupport} class.
         * 
         * @param support
         *            the support coordinates
         */
        public MinFilter(Set<Pixel> support) {
                this.support = support;

                if (FilterSupport.isBlockSupport(support)) {
                        blockWidth = FilterSupport.getSupportWidth(support);
                        blockHeight = FilterSupport.getSupportHeight(support);
                }
        }

        @Override
        public void processImage(FImage image) {
                if (blockWidth >= 1 && blockHeight >= 1) {
                        minHorizontalSym(image, blockWidth);
                        minVerticalSym(image, blockWidth);
                } else {
                        final FImage tmpImage = new FImage(image.width, image.height);

                        for (int y = 0; y < image.height; y++) {
                                for (int x = 0; x < image.width; x++) {
                                        float min = Float.MAX_VALUE;

                                        for (final Pixel sp : support) {
                                                final int xx = x + sp.x;
                                                final int yy = y + sp.y;

                                                if (xx >= 0 && xx < image.width && yy >= 0 && yy < image.height) {
                                                        min = Math.min(min, image.pixels[yy][xx]);
                                                }
                                        }

                                        tmpImage.pixels[y][x] = min;
                                }
                        }
                        image.internalAssign(tmpImage);
                }
        }

        private static void minHorizontalSym(FImage image, int width) {
                final int halfsize = width / 2;
                final float buffer[] = new float[image.width + width];

                for (int r = 0; r < image.height; r++) {
                        for (int i = 0; i < halfsize; i++)
                                buffer[i] = image.pixels[r][0];
                        for (int i = 0; i < image.width; i++)
                                buffer[halfsize + i] = image.pixels[r][i];
                        for (int i = 0; i < halfsize; i++)
                                buffer[halfsize + image.width + i] = image.pixels[r][image.width - 1];

                        final int l = buffer.length - width;
                        for (int i = 0; i < l; i++) {
                                float min = Float.MAX_VALUE;

                                for (int j = 0; j < width; j++)
                                        min = Math.min(buffer[i + j], min);

                                image.pixels[r][i] = min;
                        }
                }
        }

        private static void minVerticalSym(FImage image, int width) {
                final int halfsize = width / 2;

                final float buffer[] = new float[image.height + width];

                for (int c = 0; c < image.width; c++) {
                        for (int i = 0; i < halfsize; i++)
                                buffer[i] = image.pixels[0][c];
                        for (int i = 0; i < image.height; i++)
                                buffer[halfsize + i] = image.pixels[i][c];
                        for (int i = 0; i < halfsize; i++)
                                buffer[halfsize + image.height + i] = image.pixels[image.height - 1][c];

                        final int l = buffer.length - width;
                        for (int i = 0; i < l; i++) {
                                float min = Float.MAX_VALUE;

                                for (int j = 0; j < width; j++)
                                        min = Math.min(buffer[i + j], min);

                                buffer[i] = min;
                        }

                        for (int r = 0; r < image.height; r++)
                                image.pixels[r][c] = buffer[r];
                }
        }
}