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PlantUML is a component that allows to quickly write diagrams from text.
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package net.sourceforge.plantuml.quantization;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* Uses k-means clustering for color quantization. This tends to yield good
* results, but convergence can be slow. It is not recommended for large images.
*/
public final class KMeansQuantizer implements ColorQuantizer {
public static final KMeansQuantizer INSTANCE = new KMeansQuantizer();
private KMeansQuantizer() {
}
@Override
public Set quantize(Multiset originalColors, int maxColorCount) {
Map> clustersByCentroid = new LinkedHashMap<>();
Set centroidsToRecompute = getInitialCentroids(originalColors, maxColorCount);
for (QColor centroid : centroidsToRecompute)
clustersByCentroid.put(centroid, new HashMultiset());
for (QColor color : originalColors.getDistinctElements()) {
final int count = originalColors.count(color);
clustersByCentroid.get(color.getNearestColor(centroidsToRecompute)).add(color, count);
}
while (centroidsToRecompute.isEmpty() == false) {
recomputeCentroids(clustersByCentroid, centroidsToRecompute);
centroidsToRecompute.clear();
Set allCentroids = clustersByCentroid.keySet();
for (QColor centroid : clustersByCentroid.keySet()) {
Multiset cluster = clustersByCentroid.get(centroid);
for (QColor color : new ArrayList<>(cluster.getDistinctElements())) {
QColor newCentroid = color.getNearestColor(allCentroids);
if (newCentroid != centroid) {
final int count = cluster.count(color);
final Multiset newCluster = clustersByCentroid.get(newCentroid);
cluster.remove(color, count);
newCluster.add(color, count);
centroidsToRecompute.add(centroid);
centroidsToRecompute.add(newCentroid);
}
}
}
}
return clustersByCentroid.keySet();
}
private static void recomputeCentroids(Map> clustersByCentroid,
Set centroidsToRecompute) {
for (QColor oldCentroid : centroidsToRecompute) {
final Multiset cluster = clustersByCentroid.get(oldCentroid);
final QColor newCentroid = QColor.getCentroid(cluster);
clustersByCentroid.remove(oldCentroid);
clustersByCentroid.put(newCentroid, cluster);
}
}
private static Set getInitialCentroids(Multiset originalColors, int maxColorCount) {
// We use the Forgy initialization method: choose random colors as initial
// cluster centroids.
final List colorList = new ArrayList<>(originalColors.getDistinctElements());
Collections.shuffle(colorList);
return new HashSet<>(colorList.subList(0, maxColorCount));
}
}