quantize/PointProviderLab.java

/*
 * 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);
  }
}