android-34/com/android/systemui/monet/quantize/PointProviderLab.java

/*
 * Copyright (C) 2023 The Android Open Source Project
 *
 * 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.android.systemui.monet.quantize;

import com.android.systemui.monet.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);
    }
}