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/*
 * RgbAvgGray.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 ARGB color image into a Gray8Image. It does this
 * by averaging the R, G, and B values. Note that since the byte image is
 * signed, each unsigned byte in the ARGB word is converted to a signed integer
 * before doing the average. So the word 0x00FF8001 would get R, G, and B values
 * 127, 0, and -126 (and the average would be 0).
 * 
 * @author webb
 */
public class RgbAvgGray extends PipelineStage {
    
    /** Creates a new instance of RgbAvgGray */
    public RgbAvgGray() {
    }
    
    /**
     * Implementation of push operation from PipelineStage. Averages the R, G,
     * and B values to create a gray image of the same size. 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.ALGORITHM, 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.
             */
            final byte r = RgbVal.getR(rgbData[i]);
            final byte g = RgbVal.getG(rgbData[i]);
            final byte b = RgbVal.getB(rgbData[i]);
            /*
             * average the values to get the grayvalue
             */
            grayData[i] = (byte) ((r + g + b) / 3);
        }
        super.setOutput(gray);
    }
}