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.Collections;
021import java.util.List;
022
023import org.apache.commons.imaging.ImageWriteException;
024
025public class MostPopulatedBoxesMedianCut implements MedianCut {
026
027    @Override
028    public boolean performNextMedianCut(final List<ColorGroup> colorGroups,
029            final boolean ignoreAlpha) throws ImageWriteException {
030        int maxPoints = 0;
031        ColorGroup colorGroup = null;
032        for (final ColorGroup group : colorGroups) {
033            if (group.maxDiff > 0) {
034                if (group.totalPoints > maxPoints) {
035                    colorGroup = group;
036                    maxPoints = group.totalPoints;
037                }
038            }
039        }
040        if (colorGroup == null) {
041            return false;
042        }
043
044        final List<ColorCount> colorCounts = colorGroup.getColorCounts();
045
046        double bestScore = Double.MAX_VALUE;
047        ColorComponent bestColorComponent = null;
048        int bestMedianIndex = -1;
049        for (final ColorComponent colorComponent : ColorComponent.values()) {
050            if (ignoreAlpha && colorComponent == ColorComponent.ALPHA) {
051                continue;
052            }
053            Collections.sort(colorCounts, new ColorCountComparator(colorComponent));
054            final int countHalf = (int) Math.round((double) colorGroup.totalPoints / 2);
055            int oldCount = 0;
056            int newCount = 0;
057            int medianIndex;
058            for (medianIndex = 0; medianIndex < colorCounts.size(); medianIndex++) {
059                final ColorCount colorCount = colorCounts.get(medianIndex);
060
061                newCount += colorCount.count;
062
063                if (newCount < countHalf) {
064                    oldCount = newCount;
065                } else {
066                    break;
067                }
068            }
069            if (medianIndex == colorCounts.size() - 1) {
070                medianIndex--;
071            } else if (medianIndex > 0) {
072                final int newDiff = Math.abs(newCount - countHalf);
073                final int oldDiff = Math.abs(countHalf - oldCount);
074                if (oldDiff < newDiff) {
075                    medianIndex--;
076                }
077            }
078
079            final List<ColorCount> lowerColors = new ArrayList<>(
080                    colorCounts.subList(0, medianIndex + 1));
081            final List<ColorCount> upperColors = new ArrayList<>(
082                    colorCounts.subList(medianIndex + 1,
083                            colorCounts.size()));
084            if (lowerColors.isEmpty() || upperColors.isEmpty()) {
085                continue;
086            }
087            final ColorGroup lowerGroup = new ColorGroup(lowerColors, ignoreAlpha);
088            final ColorGroup upperGroup = new ColorGroup(upperColors, ignoreAlpha);
089            final int diff = Math.abs(lowerGroup.totalPoints - upperGroup.totalPoints);
090            final double score = diff / (double) Math.max(lowerGroup.totalPoints, upperGroup.totalPoints);
091            if (score < bestScore) {
092                bestScore = score;
093                bestColorComponent = colorComponent;
094                bestMedianIndex = medianIndex;
095            }
096        }
097
098        if (bestColorComponent == null) {
099            return false;
100        }
101
102        Collections.sort(colorCounts, new ColorCountComparator(bestColorComponent));
103        final List<ColorCount> lowerColors = new ArrayList<>(
104                colorCounts.subList(0, bestMedianIndex + 1));
105        final List<ColorCount> upperColors = new ArrayList<>(
106                colorCounts.subList(bestMedianIndex + 1,
107                        colorCounts.size()));
108        final ColorGroup lowerGroup = new ColorGroup(lowerColors, ignoreAlpha);
109        final ColorGroup upperGroup = new ColorGroup(upperColors, ignoreAlpha);
110        colorGroups.remove(colorGroup);
111        colorGroups.add(lowerGroup);
112        colorGroups.add(upperGroup);
113
114        final ColorCount medianValue = colorCounts.get(bestMedianIndex);
115        int limit;
116        switch (bestColorComponent) {
117            case ALPHA:
118                limit = medianValue.alpha;
119                break;
120            case RED:
121                limit = medianValue.red;
122                break;
123            case GREEN:
124                limit = medianValue.green;
125                break;
126            case BLUE:
127                limit = medianValue.blue;
128                break;
129            default:
130                throw new Error("Bad mode.");
131        }
132        colorGroup.cut = new ColorGroupCut(lowerGroup, upperGroup, bestColorComponent, limit);
133        return true;
134    }
135}