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/*
 * RgbAvg2Gray.java
 *
 * Created on August 27, 2006, 8:28 AM
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 *
 * Copyright 2007 by Jon A. Webb
 *     This program is free software: you can redistribute it and/or modify
 *    it under the terms of the GNU Lesser General Public License as published by
 *    the Free Software Foundation, either version 3 of the License, or
 *    (at your option) any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU Lesser General Public License for more details.
 *
 *    You should have received a copy of the Lesser GNU General Public License
 *    along with this program.  If not, see .
 *
 */

package com.github.ojil.algorithm;

import com.github.ojil.core.Gray8Image;
import com.github.ojil.core.Image;
import com.github.ojil.core.ImageError;
import com.github.ojil.core.PipelineStage;
import com.github.ojil.core.RgbImage;
import com.github.ojil.core.RgbVal;

/**
 * Pipeline stage converts an RgbImage into a Gray8Image. It does this by
 * choosing at each pixel the value that will give the maximum contrast in the
 * resulting image. That is, it computes the R, G, and B values at each pixel,
 * and chooses the most extreme value -- the one largest in absolute value.
 * 
 * @author webb
 */
public class RgbMaxContrast2Gray extends PipelineStage {
    
    /**
     * Implementation of push operation from PipelineStage. Pipeline stage
     * converts an ARGB color image into a Gray8Image. It does this by choosing
     * at each pixel the value that will give the maximum contrast in the
     * resulting image. That is, it computes the R, G, and B values at each
     * pixel, and chooses the most extreme value -- the one largest in absolute
     * value. Note that the RGB→Gray conversion involves changing the data
     * range of each pixel from 0→255 to -128→127 because byte is a
     * signed type.
     *
     * @param image
     *            the input image
     * @throws ImageError
     *             if image is not an RgbImage
     */
    @Override
    public void push(final Image image) throws ImageError {
        if (!(image instanceof RgbImage)) {
            throw new ImageError(ImageError.PACKAGE.CORE, AlgorithmErrorCodes.IMAGE_NOT_RGBIMAGE, image.toString(), null, null);
        }
        final RgbImage rgb = (RgbImage) image;
        final Integer[] rgbData = rgb.getData();
        final Gray8Image gray = new Gray8Image<>(image.getWidth(), image.getHeight());
        final Byte[] grayData = gray.getData();
        for (int i = 0; i < (image.getWidth() * image.getHeight()); i++) {
            /*
             * get individual r, g, and b values, unmasking them from the ARGB
             * word. The r, g, and b values are signed values from -128 to 127.
             */
            final byte r = RgbVal.getR(rgbData[i]);
            final byte g = RgbVal.getG(rgbData[i]);
            final byte b = RgbVal.getB(rgbData[i]);
            final int nAR = Math.abs(r);
            final int nAG = Math.abs(g);
            final int nAB = Math.abs(b);
            if ((nAR >= nAG) && (nAR >= nAB)) {
                grayData[i] = r;
            } else if (nAG >= nAB) {
                grayData[i] = g;
            } else {
                grayData[i] = b;
            }
        }
        super.setOutput(gray);
    }
}