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.util.ArrayList;
020import java.util.List;
021
022import org.apache.commons.imaging.ImageWriteException;
023
024public class MostPopulatedBoxesMedianCut implements MedianCut {
025
026    @Override
027    public boolean performNextMedianCut(final List<ColorGroup> colorGroups,
028            final boolean ignoreAlpha) throws ImageWriteException {
029        int maxPoints = 0;
030        ColorGroup colorGroup = null;
031        for (final ColorGroup group : colorGroups) {
032            if (group.maxDiff > 0) {
033                if (group.totalPoints > maxPoints) {
034                    colorGroup = group;
035                    maxPoints = group.totalPoints;
036                }
037            }
038        }
039        if (colorGroup == null) {
040            return false;
041        }
042
043        final List<ColorCount> colorCounts = colorGroup.getColorCounts();
044
045        double bestScore = Double.MAX_VALUE;
046        ColorComponent bestColorComponent = null;
047        int bestMedianIndex = -1;
048        for (final ColorComponent colorComponent : ColorComponent.values()) {
049            if (ignoreAlpha && colorComponent == ColorComponent.ALPHA) {
050                continue;
051            }
052            colorCounts.sort(new ColorCountComparator(colorComponent));
053            final int countHalf = (int) Math.round((double) colorGroup.totalPoints / 2);
054            int oldCount = 0;
055            int newCount = 0;
056            int medianIndex;
057            for (medianIndex = 0; medianIndex < colorCounts.size(); medianIndex++) {
058                final ColorCount colorCount = colorCounts.get(medianIndex);
059
060                newCount += colorCount.count;
061
062                if (newCount >= countHalf) {
063                    break;
064                }
065                oldCount = newCount;
066            }
067            if (medianIndex == colorCounts.size() - 1) {
068                medianIndex--;
069            } else if (medianIndex > 0) {
070                final int newDiff = Math.abs(newCount - countHalf);
071                final int oldDiff = Math.abs(countHalf - oldCount);
072                if (oldDiff < newDiff) {
073                    medianIndex--;
074                }
075            }
076
077            final List<ColorCount> lowerColors = new ArrayList<>(
078                    colorCounts.subList(0, medianIndex + 1));
079            final List<ColorCount> upperColors = new ArrayList<>(
080                    colorCounts.subList(medianIndex + 1,
081                            colorCounts.size()));
082            if (lowerColors.isEmpty() || upperColors.isEmpty()) {
083                continue;
084            }
085            final ColorGroup lowerGroup = new ColorGroup(lowerColors, ignoreAlpha);
086            final ColorGroup upperGroup = new ColorGroup(upperColors, ignoreAlpha);
087            final int diff = Math.abs(lowerGroup.totalPoints - upperGroup.totalPoints);
088            final double score = diff / (double) Math.max(lowerGroup.totalPoints, upperGroup.totalPoints);
089            if (score < bestScore) {
090                bestScore = score;
091                bestColorComponent = colorComponent;
092                bestMedianIndex = medianIndex;
093            }
094        }
095
096        if (bestColorComponent == null) {
097            return false;
098        }
099
100        colorCounts.sort(new ColorCountComparator(bestColorComponent));
101        final List<ColorCount> lowerColors = new ArrayList<>(
102                colorCounts.subList(0, bestMedianIndex + 1));
103        final List<ColorCount> upperColors = new ArrayList<>(
104                colorCounts.subList(bestMedianIndex + 1,
105                        colorCounts.size()));
106        final ColorGroup lowerGroup = new ColorGroup(lowerColors, ignoreAlpha);
107        final ColorGroup upperGroup = new ColorGroup(upperColors, ignoreAlpha);
108        colorGroups.remove(colorGroup);
109        colorGroups.add(lowerGroup);
110        colorGroups.add(upperGroup);
111
112        final ColorCount medianValue = colorCounts.get(bestMedianIndex);
113        int limit;
114        switch (bestColorComponent) {
115            case ALPHA:
116                limit = medianValue.alpha;
117                break;
118            case RED:
119                limit = medianValue.red;
120                break;
121            case GREEN:
122                limit = medianValue.green;
123                break;
124            case BLUE:
125                limit = medianValue.blue;
126                break;
127            default:
128                throw new Error("Bad mode.");
129        }
130        colorGroup.cut = new ColorGroupCut(lowerGroup, upperGroup, bestColorComponent, limit);
131        return true;
132    }
133}