/**
 * 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 org.openimaj.image.FImage;
import org.openimaj.image.processor.ImageProcessor;

/**
 * An {@link ImageProcessor} that computes the mean of the image's pixels
 * and subtracts the mean from all pixels.
 * 
 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
 */
public class MeanCenter implements ImageProcessor<FImage> {

        @Override
        public void processImage(FImage image) {
                final int width = image.width;
                final int height = image.height;
                final float[][] data = image.pixels;
                
                image.subtractInplace(patchMean(data, 0, 0, width, height));
        }
        
        /**
         * same as {@link #patchMean(float[][], int, int, int, int)} but the width and height are taken from data[0].length and data.length
         * @param data
         * @return the patch mean
         */
        public static final float patchMean(final float[][] data){
                return patchMean(data, 0, 0, data.length > 0 && data[0]!=null ? data[0].length : 0, data.length);
        }
        /**
         * Finds the mean value of a sub-patch of a 2D float array.
         * @param data the array
         * @param x the location of the sub-patch
         * @param y the location of the sub-patch
         * @param width sub-patch width
         * @param height sub-patch height
         * @return the mean value
         */
        public static final float patchMean(final float[][] data, final int x, final int y, final int width, final int height) {
                float accum = 0;
                
                final int endX = width + x;
                final int endY = height + y;
                
                for (int yy=y; yy<endY; yy++) {
                        for (int xx=x; xx<endX; xx++) {
                                accum += data[yy][xx];
                        }
                }
                
                float mean = accum / (float)(width * height);
                return mean;
        }
}