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/*
* Copyright 2021 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.ux.material.libmonet.quantize;
import java.util.Map;
import java.util.Set;
/**
* An image quantizer that improves on the quality of a standard K-Means algorithm by setting the
* K-Means initial state to the output of a Wu quantizer, instead of random centroids. Improves on
* speed by several optimizations, as implemented in Wsmeans, or Weighted Square Means, K-Means with
* those optimizations.
*
* <p>This algorithm was designed by M. Emre Celebi, and was found in their 2011 paper, Improving
* the Performance of K-Means for Color Quantization. https://arxiv.org/abs/1101.0395
*/
public final class QuantizerCelebi {
private QuantizerCelebi() {}
/**
* Reduce the number of colors needed to represented the input, minimizing the difference between
* the original image and the recolored image.
*
* @param pixels Colors in ARGB format.
* @param maxColors The number of colors to divide the image into. A lower number of colors may be
* returned.
* @return Map with keys of colors in ARGB format, and values of number of pixels in the original
* image that correspond to the color in the quantized image.
*/
public static Map<Integer, Integer> quantize(int[] pixels, int maxColors) {
QuantizerWu wu = new QuantizerWu();
QuantizerResult wuResult = wu.quantize(pixels, maxColors);
Set<Integer> wuClustersAsObjects = wuResult.colorToCount.keySet();
int index = 0;
int[] wuClusters = new int[wuClustersAsObjects.size()];
for (Integer argb : wuClustersAsObjects) {
wuClusters[index++] = argb;
}
return QuantizerWsmeans.quantize(pixels, wuClusters, maxColors);
}
}
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