001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.imaging.palette;
018
019import java.awt.image.BufferedImage;
020
021import org.apache.commons.imaging.ImageWriteException;
022
023/**
024 * Dithering algorithms to use when quantizing an image to palette form.
025 */
026public final class Dithering {
027    private Dithering() {
028    }
029
030    /**
031     * Changes the given image to only use colors from the given palette,
032     * applying Floyd-Steinberg dithering in the process. Ensure that
033     * your alpha values in the image and in the palette are consistent.
034     *
035     * @param image   the image to change
036     * @param palette the palette to use
037     * @throws ImageWriteException if it fails to read the palette index
038     */
039    public static void applyFloydSteinbergDithering(final BufferedImage image, final Palette palette) throws ImageWriteException {
040        for (int y = 0; y < image.getHeight(); y++) {
041            for (int x = 0; x < image.getWidth(); x++) {
042                final int argb = image.getRGB(x, y);
043                final int index = palette.getPaletteIndex(argb);
044                final int nextArgb = palette.getEntry(index);
045                image.setRGB(x, y, nextArgb);
046
047                final int a = (argb >> 24) & 0xff;
048                final int r = (argb >> 16) & 0xff;
049                final int g = (argb >> 8) & 0xff;
050                final int b = argb & 0xff;
051
052                final int na = (nextArgb >> 24) & 0xff;
053                final int nr = (nextArgb >> 16) & 0xff;
054                final int ng = (nextArgb >> 8) & 0xff;
055                final int nb = nextArgb & 0xff;
056
057                final int errA = a - na;
058                final int errR = r - nr;
059                final int errG = g - ng;
060                final int errB = b - nb;
061
062                if (x + 1 < image.getWidth()) {
063                    int update = adjustPixel(image.getRGB(x + 1, y), errA, errR, errG, errB, 7);
064                    image.setRGB(x + 1, y, update);
065                    if (y + 1 < image.getHeight()) {
066                        update = adjustPixel(image.getRGB(x + 1, y + 1), errA, errR, errG, errB, 1);
067                        image.setRGB(x + 1, y + 1, update);
068                    }
069                }
070                if (y + 1 < image.getHeight()) {
071                    int update = adjustPixel(image.getRGB(x, y + 1), errA, errR, errG, errB, 5);
072                    image.setRGB(x, y + 1, update);
073                    if (x - 1 >= 0) {
074                        update = adjustPixel(image.getRGB(x - 1, y + 1), errA, errR, errG, errB, 3);
075                        image.setRGB(x - 1, y + 1, update);
076                    }
077
078                }
079            }
080        }
081    }
082
083    private static int adjustPixel(final int argb, final int errA, final int errR, final int errG, final int errB, final int mul) {
084        int a = (argb >> 24) & 0xff;
085        int r = (argb >> 16) & 0xff;
086        int g = (argb >> 8) & 0xff;
087        int b = argb & 0xff;
088
089        a += errA * mul / 16;
090        r += errR * mul / 16;
091        g += errG * mul / 16;
092        b += errB * mul / 16;
093
094        if (a < 0) {
095            a = 0;
096        } else if (a > 0xff) {
097            a = 0xff;
098        }
099        if (r < 0) {
100            r = 0;
101        } else if (r > 0xff) {
102            r = 0xff;
103        }
104        if (g < 0) {
105            g = 0;
106        } else if (g > 0xff) {
107            g = 0xff;
108        }
109        if (b < 0) {
110            b = 0;
111        } else if (b > 0xff) {
112            b = 0xff;
113        }
114
115        return (a << 24) | (r << 16) | (g << 8) | b;
116    }
117}