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.ImagingException; 022 023/** 024 * Dithering algorithms to use when quantizing an image to palette form. 025 */ 026public final class Dithering { 027 private static int adjustPixel(final int argb, final int errA, final int errR, final int errG, final int errB, final int mul) { 028 int a = argb >> 24 & 0xff; 029 int r = argb >> 16 & 0xff; 030 int g = argb >> 8 & 0xff; 031 int b = argb & 0xff; 032 033 a += errA * mul / 16; 034 r += errR * mul / 16; 035 g += errG * mul / 16; 036 b += errB * mul / 16; 037 038 if (a < 0) { 039 a = 0; 040 } else if (a > 0xff) { 041 a = 0xff; 042 } 043 if (r < 0) { 044 r = 0; 045 } else if (r > 0xff) { 046 r = 0xff; 047 } 048 if (g < 0) { 049 g = 0; 050 } else if (g > 0xff) { 051 g = 0xff; 052 } 053 if (b < 0) { 054 b = 0; 055 } else if (b > 0xff) { 056 b = 0xff; 057 } 058 059 return a << 24 | r << 16 | g << 8 | b; 060 } 061 062 /** 063 * Changes the given image to only use colors from the given palette, applying Floyd-Steinberg dithering in the process. Ensure that your alpha values in 064 * the image and in the palette are consistent. 065 * 066 * @param image the image to change 067 * @param palette the palette to use 068 * @throws ImagingException if it fails to read the palette index 069 */ 070 public static void applyFloydSteinbergDithering(final BufferedImage image, final Palette palette) throws ImagingException { 071 for (int y = 0; y < image.getHeight(); y++) { 072 for (int x = 0; x < image.getWidth(); x++) { 073 final int argb = image.getRGB(x, y); 074 final int index = palette.getPaletteIndex(argb); 075 final int nextArgb = palette.getEntry(index); 076 image.setRGB(x, y, nextArgb); 077 078 final int a = argb >> 24 & 0xff; 079 final int r = argb >> 16 & 0xff; 080 final int g = argb >> 8 & 0xff; 081 final int b = argb & 0xff; 082 083 final int na = nextArgb >> 24 & 0xff; 084 final int nr = nextArgb >> 16 & 0xff; 085 final int ng = nextArgb >> 8 & 0xff; 086 final int nb = nextArgb & 0xff; 087 088 final int errA = a - na; 089 final int errR = r - nr; 090 final int errG = g - ng; 091 final int errB = b - nb; 092 093 if (x + 1 < image.getWidth()) { 094 int update = adjustPixel(image.getRGB(x + 1, y), errA, errR, errG, errB, 7); 095 image.setRGB(x + 1, y, update); 096 if (y + 1 < image.getHeight()) { 097 update = adjustPixel(image.getRGB(x + 1, y + 1), errA, errR, errG, errB, 1); 098 image.setRGB(x + 1, y + 1, update); 099 } 100 } 101 if (y + 1 < image.getHeight()) { 102 int update = adjustPixel(image.getRGB(x, y + 1), errA, errR, errG, errB, 5); 103 image.setRGB(x, y + 1, update); 104 if (x - 1 >= 0) { 105 update = adjustPixel(image.getRGB(x - 1, y + 1), errA, errR, errG, errB, 3); 106 image.setRGB(x - 1, y + 1, update); 107 } 108 109 } 110 } 111 } 112 } 113 114 private Dithering() { 115 // no instances. 116 } 117}