http://xmlgraphics.apache.org/fop/: Apache FOP (Formatting Objects Processor) is the world's first print formatter driven by XSL formatting objects (XSL-FO) and the world's first output independent formatter. It is a Java application that reads a formatting object (FO) tree and renders the resulting pages to a specified output. Output formats currently supported include PDF, PCL, PS, AFP, TIFF, PNG, SVG, XML (area tree representation), Print, AWT and TXT. The primary output target is PDF. (Apache Software Foundation) 
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 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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/* $Id: DitherUtil.java 1785982 2017-03-08 15:15:06Z ssteiner $ */

package org.apache.fop.util.bitmap;

import java.awt.Color;


Utility methods for dithering.

/**
 * Utility methods for dithering.
 */
public final class DitherUtil {

    private DitherUtil() {
    }

    
Selects a 2x2 Bayer dither matrix (5 grayscales) 
/** Selects a 2x2 Bayer dither matrix (5 grayscales) */
    public static final int DITHER_MATRIX_2X2 = 2;
    
Selects a 4x4 Bayer dither matrix (17 grayscales) 
/** Selects a 4x4 Bayer dither matrix (17 grayscales) */
    public static final int DITHER_MATRIX_4X4 = 4;
    
Selects a 8x8 Bayer dither matrix (65 grayscales) 
/** Selects a 8x8 Bayer dither matrix (65 grayscales) */
    public static final int DITHER_MATRIX_8X8 = 8;

    //Bayer dither matrices (4x4 and 8x8 are derived from the 2x2 matrix)
    private static final int[] BAYER_D2 = new int[] {0, 2, 3, 1};
    private static final int[] BAYER_D4;
    private static final int[] BAYER_D8;

    static {
        BAYER_D4 = deriveBayerMatrix(BAYER_D2);
        BAYER_D8 = deriveBayerMatrix(BAYER_D4);
    }

    private static int[] deriveBayerMatrix(int[] d) {
        int[] dn = new int[d.length * 4];
        int half = (int)Math.sqrt(d.length);
        for (int part = 0; part < 4; part++) {
            for (int i = 0, c = d.length; i < c; i++) {
                setValueInMatrix(dn, half, part, i, d[i] * 4 + BAYER_D2[part]);
            }
        }
        return dn;
    }

    private static void setValueInMatrix(int[] dn, int half, int part, int idx, int value) {
        int xoff = (part & 1) * half;
        int yoff = (part & 2) * half * half;
        int matrixIndex = yoff + ((idx / half) * half * 2) + (idx % half) + xoff;
        dn[matrixIndex] = value;
    }

    
Returns the Bayer dither base pattern for a particular matrix size.

Params:
Returns:the base pattern for the given size
/**
     * Returns the Bayer dither base pattern for a particular matrix size.
     * @param matrix the matrix size ({@link #DITHER_MATRIX_2X2}, {@link #DITHER_MATRIX_4X4}
     *                                   or {@link #DITHER_MATRIX_8X8})
     * @return the base pattern for the given size
     */
    public static int[] getBayerBasePattern(int matrix) {
        int[] result = new int[matrix * matrix];
        switch (matrix) {
        case DITHER_MATRIX_2X2:
            System.arraycopy(BAYER_D2, 0, result, 0, BAYER_D2.length);
            break;
        case DITHER_MATRIX_4X4:
            System.arraycopy(BAYER_D4, 0, result, 0, BAYER_D4.length);
            break;
        case DITHER_MATRIX_8X8:
            System.arraycopy(BAYER_D8, 0, result, 0, BAYER_D8.length);
            break;
        default:
            throw new IllegalArgumentException("Unsupported dither matrix: " + matrix);
        }
        return result;
    }

    
Returns a byte array containing the dither pattern for the given 8-bit gray value.

Params:
Returns:the dither pattern
/**
     * Returns a byte array containing the dither pattern for the given 8-bit gray value.
     * @param matrix the matrix size ({@link #DITHER_MATRIX_2X2}, {@link #DITHER_MATRIX_4X4}
     *                                   or {@link #DITHER_MATRIX_8X8})
     * @param gray255 the gray value (0-255)
     * @param doubleMatrix true if the 4x4 matrix shall be doubled to a 8x8
     * @return the dither pattern
     */
    public static byte[] getBayerDither(int matrix, int gray255, boolean doubleMatrix) {
        int ditherIndex;
        byte[] dither;
        int[] bayer;
        switch (matrix) {
        case DITHER_MATRIX_4X4:
            ditherIndex = gray255 * 17 / 255;
            bayer = BAYER_D4;
            break;
        case DITHER_MATRIX_8X8:
            ditherIndex = gray255 * 65 / 255;
            bayer = BAYER_D8;
            break;
        default:
            throw new IllegalArgumentException("Unsupported dither matrix: " + matrix);
        }
        if (doubleMatrix) {
            if (matrix != DITHER_MATRIX_4X4) {
                throw new IllegalArgumentException("doubleMatrix=true is only allowed for 4x4");
            }
            dither = new byte[bayer.length / 8 * 4];
            for (int i = 0, c = bayer.length; i < c; i++) {
                boolean dot = !(bayer[i] < ditherIndex - 1);
                if (dot) {
                    int byteIdx = i / 4;
                    dither[byteIdx] |= 1 << (i % 4);
                    dither[byteIdx] |= 1 << ((i % 4) + 4);
                    dither[byteIdx + 4] |= 1 << (i % 4);
                    dither[byteIdx + 4] |= 1 << ((i % 4) + 4);
                }
            }
        } else {
            dither = new byte[bayer.length / 8];
            for (int i = 0, c = bayer.length; i < c; i++) {
                boolean dot = !(bayer[i] < ditherIndex - 1);
                if (dot) {
                    int byteIdx = i / 8;
                    dither[byteIdx] |= 1 << (i % 8);
                }
            }
        }
        return dither;
    }

    
Returns a byte array containing the dither pattern for the given 8-bit gray value.

Params:
Returns:the dither pattern
/**
     * Returns a byte array containing the dither pattern for the given 8-bit gray value.
     * @param matrix the matrix size ({@link #DITHER_MATRIX_2X2}, {@link #DITHER_MATRIX_4X4}
     *                                   or {@link #DITHER_MATRIX_8X8})
     * @param col the color
     * @param doubleMatrix true if the 4x4 matrix shall be doubled to a 8x8
     * @return the dither pattern
     */
    public static byte[] getBayerDither(int matrix, Color col, boolean doubleMatrix) {
        float black = BitmapImageUtil.convertToGray(col.getRGB()) / 256f;
        return getBayerDither(matrix, Math.round(black * 256), doubleMatrix);
    }

}