    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}