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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 com.google.ux.material.libmonet.utils.ColorUtils;
/**
* Provides conversions needed for K-Means quantization. Converting input to points, and converting
* the final state of the K-Means algorithm to colors.
*/
public final class PointProviderLab implements PointProvider {
/**
* Convert a color represented in ARGB to a 3-element array of L*a*b* coordinates of the color.
*/
@Override
public double[] fromInt(int argb) {
double[] lab = ColorUtils.labFromArgb(argb);
return new double[] {lab[0], lab[1], lab[2]};
}
/** Convert a 3-element array to a color represented in ARGB. */
@Override
public int toInt(double[] lab) {
return ColorUtils.argbFromLab(lab[0], lab[1], lab[2]);
}
/**
* Standard CIE 1976 delta E formula also takes the square root, unneeded here. This method is
* used by quantization algorithms to compare distance, and the relative ordering is the same,
* with or without a square root.
*
* <p>This relatively minor optimization is helpful because this method is called at least once
* for each pixel in an image.
*/
@Override
public double distance(double[] one, double[] two) {
double dL = (one[0] - two[0]);
double dA = (one[1] - two[1]);
double dB = (one[2] - two[2]);
return (dL * dL + dA * dA + dB * dB);
}
}
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