    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.Comparator;
    021import java.util.List;
    022
    023import org.apache.commons.imaging.ImagingException;
    024
    025public class LongestAxisMedianCut implements MedianCut {
    026    private static final Comparator<ColorGroup> COMPARATOR = (cg1, cg2) -> {
    027        if (cg1.maxDiff == cg2.maxDiff) {
    028            return cg2.diffTotal - cg1.diffTotal;
    029        }
    030        return cg2.maxDiff - cg1.maxDiff;
    031    };
    032
    033    private void doCut(final ColorGroup colorGroup, final ColorComponent mode, final List<ColorGroup> colorGroups, final boolean ignoreAlpha)
    034            throws ImagingException {
    035
    036        final List<ColorCount> colorCounts = colorGroup.getColorCounts();
    037        colorCounts.sort(new ColorCountComparator(mode));
    038        final int countHalf = (int) Math.round((double) colorGroup.totalPoints / 2);
    039        int oldCount = 0;
    040        int newCount = 0;
    041        int medianIndex;
    042        for (medianIndex = 0; medianIndex < colorCounts.size(); medianIndex++) {
    043            final ColorCount colorCount = colorCounts.get(medianIndex);
    044
    045            newCount += colorCount.count;
    046
    047            if (newCount >= countHalf) {
    048                break;
    049            }
    050            oldCount = newCount;
    051        }
    052
    053        if (medianIndex == colorCounts.size() - 1) {
    054            medianIndex--;
    055        } else if (medianIndex > 0) {
    056            final int newDiff = Math.abs(newCount - countHalf);
    057            final int oldDiff = Math.abs(countHalf - oldCount);
    058            if (oldDiff < newDiff) {
    059                medianIndex--;
    060            }
    061        }
    062
    063        colorGroups.remove(colorGroup);
    064        final List<ColorCount> colorCounts1 = new ArrayList<>(colorCounts.subList(0, medianIndex + 1));
    065        final List<ColorCount> colorCounts2 = new ArrayList<>(colorCounts.subList(medianIndex + 1, colorCounts.size()));
    066
    067        final ColorGroup less = new ColorGroup(new ArrayList<>(colorCounts1), ignoreAlpha);
    068        colorGroups.add(less);
    069        final ColorGroup more = new ColorGroup(new ArrayList<>(colorCounts2), ignoreAlpha);
    070        colorGroups.add(more);
    071
    072        final ColorCount medianValue = colorCounts.get(medianIndex);
    073        final int limit;
    074        switch (mode) {
    075        case ALPHA:
    076            limit = medianValue.alpha;
    077            break;
    078        case RED:
    079            limit = medianValue.red;
    080            break;
    081        case GREEN:
    082            limit = medianValue.green;
    083            break;
    084        case BLUE:
    085            limit = medianValue.blue;
    086            break;
    087        default:
    088            throw new IllegalArgumentException("Bad mode " + mode);
    089        }
    090        colorGroup.cut = new ColorGroupCut(less, more, mode, limit);
    091    }
    092
    093    @Override
    094    public boolean performNextMedianCut(final List<ColorGroup> colorGroups, final boolean ignoreAlpha) throws ImagingException {
    095        colorGroups.sort(COMPARATOR);
    096        final ColorGroup colorGroup = colorGroups.get(0);
    097
    098        if (colorGroup.maxDiff == 0) {
    099            return false;
    100        }
    101        if (!ignoreAlpha && colorGroup.alphaDiff > colorGroup.redDiff && colorGroup.alphaDiff > colorGroup.greenDiff
    102                && colorGroup.alphaDiff > colorGroup.blueDiff) {
    103            doCut(colorGroup, ColorComponent.ALPHA, colorGroups, ignoreAlpha);
    104        } else if (colorGroup.redDiff > colorGroup.greenDiff && colorGroup.redDiff > colorGroup.blueDiff) {
    105            doCut(colorGroup, ColorComponent.RED, colorGroups, ignoreAlpha);
    106        } else if (colorGroup.greenDiff > colorGroup.blueDiff) {
    107            doCut(colorGroup, ColorComponent.GREEN, colorGroups, ignoreAlpha);
    108        } else {
    109            doCut(colorGroup, ColorComponent.BLUE, colorGroups, ignoreAlpha);
    110        }
    111        return true;
    112    }
    113}