xref: /aosp_15_r20/external/libmonet/hct/Cam16.java (revision 970e10460f970939fd510dd6ad3e0d65908272e3)

/*
 * 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.hct;

import static java.lang.Math.max;

import com.google.ux.material.libmonet.utils.ColorUtils;

/**
 * CAM16, a color appearance model. Colors are not just defined by their hex code, but rather, a hex
 * code and viewing conditions.
 *
 * <p>CAM16 instances also have coordinates in the CAM16-UCS space, called J*, a*, b*, or jstar,
 * astar, bstar in code. CAM16-UCS is included in the CAM16 specification, and should be used when
 * measuring distances between colors.
 *
 * <p>In traditional color spaces, a color can be identified solely by the observer's measurement of
 * the color. Color appearance models such as CAM16 also use information about the environment where
 * the color was observed, known as the viewing conditions.
 *
 * <p>For example, white under the traditional assumption of a midday sun white point is accurately
 * measured as a slightly chromatic blue by CAM16. (roughly, hue 203, chroma 3, lightness 100)
 */
public final class Cam16 {
  // Transforms XYZ color space coordinates to 'cone'/'RGB' responses in CAM16.
  static final double[][] XYZ_TO_CAM16RGB = {
    {0.401288, 0.650173, -0.051461},
    {-0.250268, 1.204414, 0.045854},
    {-0.002079, 0.048952, 0.953127}
  };

  // Transforms 'cone'/'RGB' responses in CAM16 to XYZ color space coordinates.
  static final double[][] CAM16RGB_TO_XYZ = {
    {1.8620678, -1.0112547, 0.14918678},
    {0.38752654, 0.62144744, -0.00897398},
    {-0.01584150, -0.03412294, 1.0499644}
  };

  // CAM16 color dimensions, see getters for documentation.
  private final double hue;
  private final double chroma;
  private final double j;
  private final double q;
  private final double m;
  private final double s;

  // Coordinates in UCS space. Used to determine color distance, like delta E equations in L*a*b*.
  private final double jstar;
  private final double astar;
  private final double bstar;

  // Avoid allocations during conversion by pre-allocating an array.
  private final double[] tempArray = new double[] {0.0, 0.0, 0.0};

  /**
   * CAM16 instances also have coordinates in the CAM16-UCS space, called J*, a*, b*, or jstar,
   * astar, bstar in code. CAM16-UCS is included in the CAM16 specification, and is used to measure
   * distances between colors.
   */
  public double distance(Cam16 other) {
    double dJ = getJstar() - other.getJstar();
    double dA = getAstar() - other.getAstar();
    double dB = getBstar() - other.getBstar();
    double dEPrime = Math.sqrt(dJ * dJ + dA * dA + dB * dB);
    double dE = 1.41 * Math.pow(dEPrime, 0.63);
    return dE;
  }

  /** Hue in CAM16 */
  public double getHue() {
    return hue;
  }

  /** Chroma in CAM16 */
  public double getChroma() {
    return chroma;
  }

  /** Lightness in CAM16 */
  public double getJ() {
    return j;
  }

  /**
   * Brightness in CAM16.
   *
   * <p>Prefer lightness, brightness is an absolute quantity. For example, a sheet of white paper is
   * much brighter viewed in sunlight than in indoor light, but it is the lightest object under any
   * lighting.
   */
  public double getQ() {
    return q;
  }

  /**
   * Colorfulness in CAM16.
   *
   * <p>Prefer chroma, colorfulness is an absolute quantity. For example, a yellow toy car is much
   * more colorful outside than inside, but it has the same chroma in both environments.
   */
  public double getM() {
    return m;
  }

  /**
   * Saturation in CAM16.
   *
   * <p>Colorfulness in proportion to brightness. Prefer chroma, saturation measures colorfulness
   * relative to the color's own brightness, where chroma is colorfulness relative to white.
   */
  public double getS() {
    return s;
  }

  /** Lightness coordinate in CAM16-UCS */
  public double getJstar() {
    return jstar;
  }

  /** a* coordinate in CAM16-UCS */
  public double getAstar() {
    return astar;
  }

  /** b* coordinate in CAM16-UCS */
  public double getBstar() {
    return bstar;
  }

  /**
   * All of the CAM16 dimensions can be calculated from 3 of the dimensions, in the following
   * combinations: - {j or q} and {c, m, or s} and hue - jstar, astar, bstar Prefer using a static
   * method that constructs from 3 of those dimensions. This constructor is intended for those
   * methods to use to return all possible dimensions.
   *
   * @param hue for example, red, orange, yellow, green, etc.
   * @param chroma informally, colorfulness / color intensity. like saturation in HSL, except
   *     perceptually accurate.
   * @param j lightness
   * @param q brightness; ratio of lightness to white point's lightness
   * @param m colorfulness
   * @param s saturation; ratio of chroma to white point's chroma
   * @param jstar CAM16-UCS J coordinate
   * @param astar CAM16-UCS a coordinate
   * @param bstar CAM16-UCS b coordinate
   */
  private Cam16(
      double hue,
      double chroma,
      double j,
      double q,
      double m,
      double s,
      double jstar,
      double astar,
      double bstar) {
    this.hue = hue;
    this.chroma = chroma;
    this.j = j;
    this.q = q;
    this.m = m;
    this.s = s;
    this.jstar = jstar;
    this.astar = astar;
    this.bstar = bstar;
  }

  /**
   * Create a CAM16 color from a color, assuming the color was viewed in default viewing conditions.
   *
   * @param argb ARGB representation of a color.
   */
  public static Cam16 fromInt(int argb) {
    return fromIntInViewingConditions(argb, ViewingConditions.DEFAULT);
  }

  /**
   * Create a CAM16 color from a color in defined viewing conditions.
   *
   * @param argb ARGB representation of a color.
   * @param viewingConditions Information about the environment where the color was observed.
   */
  // The RGB => XYZ conversion matrix elements are derived scientific constants. While the values
  // may differ at runtime due to floating point imprecision, keeping the values the same, and
  // accurate, across implementations takes precedence.
  @SuppressWarnings("FloatingPointLiteralPrecision")
  static Cam16 fromIntInViewingConditions(int argb, ViewingConditions viewingConditions) {
    // Transform ARGB int to XYZ
    int red = (argb & 0x00ff0000) >> 16;
    int green = (argb & 0x0000ff00) >> 8;
    int blue = (argb & 0x000000ff);
    double redL = ColorUtils.linearized(red);
    double greenL = ColorUtils.linearized(green);
    double blueL = ColorUtils.linearized(blue);
    double x = 0.41233895 * redL + 0.35762064 * greenL + 0.18051042 * blueL;
    double y = 0.2126 * redL + 0.7152 * greenL + 0.0722 * blueL;
    double z = 0.01932141 * redL + 0.11916382 * greenL + 0.95034478 * blueL;

    return fromXyzInViewingConditions(x, y, z, viewingConditions);
  }

  static Cam16 fromXyzInViewingConditions(
      double x, double y, double z, ViewingConditions viewingConditions) {
    // Transform XYZ to 'cone'/'rgb' responses
    double[][] matrix = XYZ_TO_CAM16RGB;
    double rT = (x * matrix[0][0]) + (y * matrix[0][1]) + (z * matrix[0][2]);
    double gT = (x * matrix[1][0]) + (y * matrix[1][1]) + (z * matrix[1][2]);
    double bT = (x * matrix[2][0]) + (y * matrix[2][1]) + (z * matrix[2][2]);

    // Discount illuminant
    double rD = viewingConditions.getRgbD()[0] * rT;
    double gD = viewingConditions.getRgbD()[1] * gT;
    double bD = viewingConditions.getRgbD()[2] * bT;

    // Chromatic adaptation
    double rAF = Math.pow(viewingConditions.getFl() * Math.abs(rD) / 100.0, 0.42);
    double gAF = Math.pow(viewingConditions.getFl() * Math.abs(gD) / 100.0, 0.42);
    double bAF = Math.pow(viewingConditions.getFl() * Math.abs(bD) / 100.0, 0.42);
    double rA = Math.signum(rD) * 400.0 * rAF / (rAF + 27.13);
    double gA = Math.signum(gD) * 400.0 * gAF / (gAF + 27.13);
    double bA = Math.signum(bD) * 400.0 * bAF / (bAF + 27.13);

    // redness-greenness
    double a = (11.0 * rA + -12.0 * gA + bA) / 11.0;
    // yellowness-blueness
    double b = (rA + gA - 2.0 * bA) / 9.0;

    // auxiliary components
    double u = (20.0 * rA + 20.0 * gA + 21.0 * bA) / 20.0;
    double p2 = (40.0 * rA + 20.0 * gA + bA) / 20.0;

    // hue
    double atan2 = Math.atan2(b, a);
    double atanDegrees = Math.toDegrees(atan2);
    double hue =
        atanDegrees < 0
            ? atanDegrees + 360.0
            : atanDegrees >= 360 ? atanDegrees - 360.0 : atanDegrees;
    double hueRadians = Math.toRadians(hue);

    // achromatic response to color
    double ac = p2 * viewingConditions.getNbb();

    // CAM16 lightness and brightness
    double j =
        100.0
            * Math.pow(
                ac / viewingConditions.getAw(),
                viewingConditions.getC() * viewingConditions.getZ());
    double q =
        4.0
            / viewingConditions.getC()
            * Math.sqrt(j / 100.0)
            * (viewingConditions.getAw() + 4.0)
            * viewingConditions.getFlRoot();

    // CAM16 chroma, colorfulness, and saturation.
    double huePrime = (hue < 20.14) ? hue + 360 : hue;
    double eHue = 0.25 * (Math.cos(Math.toRadians(huePrime) + 2.0) + 3.8);
    double p1 = 50000.0 / 13.0 * eHue * viewingConditions.getNc() * viewingConditions.getNcb();
    double t = p1 * Math.hypot(a, b) / (u + 0.305);
    double alpha =
        Math.pow(1.64 - Math.pow(0.29, viewingConditions.getN()), 0.73) * Math.pow(t, 0.9);
    // CAM16 chroma, colorfulness, saturation
    double c = alpha * Math.sqrt(j / 100.0);
    double m = c * viewingConditions.getFlRoot();
    double s =
        50.0 * Math.sqrt((alpha * viewingConditions.getC()) / (viewingConditions.getAw() + 4.0));

    // CAM16-UCS components
    double jstar = (1.0 + 100.0 * 0.007) * j / (1.0 + 0.007 * j);
    double mstar = 1.0 / 0.0228 * Math.log1p(0.0228 * m);
    double astar = mstar * Math.cos(hueRadians);
    double bstar = mstar * Math.sin(hueRadians);

    return new Cam16(hue, c, j, q, m, s, jstar, astar, bstar);
  }

  /**
   * @param j CAM16 lightness
   * @param c CAM16 chroma
   * @param h CAM16 hue
   */
  static Cam16 fromJch(double j, double c, double h) {
    return fromJchInViewingConditions(j, c, h, ViewingConditions.DEFAULT);
  }

  /**
   * @param j CAM16 lightness
   * @param c CAM16 chroma
   * @param h CAM16 hue
   * @param viewingConditions Information about the environment where the color was observed.
   */
  private static Cam16 fromJchInViewingConditions(
      double j, double c, double h, ViewingConditions viewingConditions) {
    double q =
        4.0
            / viewingConditions.getC()
            * Math.sqrt(j / 100.0)
            * (viewingConditions.getAw() + 4.0)
            * viewingConditions.getFlRoot();
    double m = c * viewingConditions.getFlRoot();
    double alpha = c / Math.sqrt(j / 100.0);
    double s =
        50.0 * Math.sqrt((alpha * viewingConditions.getC()) / (viewingConditions.getAw() + 4.0));

    double hueRadians = Math.toRadians(h);
    double jstar = (1.0 + 100.0 * 0.007) * j / (1.0 + 0.007 * j);
    double mstar = 1.0 / 0.0228 * Math.log1p(0.0228 * m);
    double astar = mstar * Math.cos(hueRadians);
    double bstar = mstar * Math.sin(hueRadians);
    return new Cam16(h, c, j, q, m, s, jstar, astar, bstar);
  }

  /**
   * Create a CAM16 color from CAM16-UCS coordinates.
   *
   * @param jstar CAM16-UCS lightness.
   * @param astar CAM16-UCS a dimension. Like a* in L*a*b*, it is a Cartesian coordinate on the Y
   *     axis.
   * @param bstar CAM16-UCS b dimension. Like a* in L*a*b*, it is a Cartesian coordinate on the X
   *     axis.
   */
  public static Cam16 fromUcs(double jstar, double astar, double bstar) {

    return fromUcsInViewingConditions(jstar, astar, bstar, ViewingConditions.DEFAULT);
  }

  /**
   * Create a CAM16 color from CAM16-UCS coordinates in defined viewing conditions.
   *
   * @param jstar CAM16-UCS lightness.
   * @param astar CAM16-UCS a dimension. Like a* in L*a*b*, it is a Cartesian coordinate on the Y
   *     axis.
   * @param bstar CAM16-UCS b dimension. Like a* in L*a*b*, it is a Cartesian coordinate on the X
   *     axis.
   * @param viewingConditions Information about the environment where the color was observed.
   */
  public static Cam16 fromUcsInViewingConditions(
      double jstar, double astar, double bstar, ViewingConditions viewingConditions) {

    double m = Math.hypot(astar, bstar);
    double m2 = Math.expm1(m * 0.0228) / 0.0228;
    double c = m2 / viewingConditions.getFlRoot();
    double h = Math.atan2(bstar, astar) * (180.0 / Math.PI);
    if (h < 0.0) {
      h += 360.0;
    }
    double j = jstar / (1. - (jstar - 100.) * 0.007);
    return fromJchInViewingConditions(j, c, h, viewingConditions);
  }

  /**
   * ARGB representation of the color. Assumes the color was viewed in default viewing conditions,
   * which are near-identical to the default viewing conditions for sRGB.
   */
  public int toInt() {
    return viewed(ViewingConditions.DEFAULT);
  }

  /**
   * ARGB representation of the color, in defined viewing conditions.
   *
   * @param viewingConditions Information about the environment where the color will be viewed.
   * @return ARGB representation of color
   */
  int viewed(ViewingConditions viewingConditions) {
    double[] xyz = xyzInViewingConditions(viewingConditions, tempArray);
    return ColorUtils.argbFromXyz(xyz[0], xyz[1], xyz[2]);
  }

  double[] xyzInViewingConditions(ViewingConditions viewingConditions, double[] returnArray) {
    double alpha =
        (getChroma() == 0.0 || getJ() == 0.0) ? 0.0 : getChroma() / Math.sqrt(getJ() / 100.0);

    double t =
        Math.pow(
            alpha / Math.pow(1.64 - Math.pow(0.29, viewingConditions.getN()), 0.73), 1.0 / 0.9);
    double hRad = Math.toRadians(getHue());

    double eHue = 0.25 * (Math.cos(hRad + 2.0) + 3.8);
    double ac =
        viewingConditions.getAw()
            * Math.pow(getJ() / 100.0, 1.0 / viewingConditions.getC() / viewingConditions.getZ());
    double p1 = eHue * (50000.0 / 13.0) * viewingConditions.getNc() * viewingConditions.getNcb();
    double p2 = (ac / viewingConditions.getNbb());

    double hSin = Math.sin(hRad);
    double hCos = Math.cos(hRad);

    double gamma = 23.0 * (p2 + 0.305) * t / (23.0 * p1 + 11.0 * t * hCos + 108.0 * t * hSin);
    double a = gamma * hCos;
    double b = gamma * hSin;
    double rA = (460.0 * p2 + 451.0 * a + 288.0 * b) / 1403.0;
    double gA = (460.0 * p2 - 891.0 * a - 261.0 * b) / 1403.0;
    double bA = (460.0 * p2 - 220.0 * a - 6300.0 * b) / 1403.0;

    double rCBase = max(0, (27.13 * Math.abs(rA)) / (400.0 - Math.abs(rA)));
    double rC =
        Math.signum(rA) * (100.0 / viewingConditions.getFl()) * Math.pow(rCBase, 1.0 / 0.42);
    double gCBase = max(0, (27.13 * Math.abs(gA)) / (400.0 - Math.abs(gA)));
    double gC =
        Math.signum(gA) * (100.0 / viewingConditions.getFl()) * Math.pow(gCBase, 1.0 / 0.42);
    double bCBase = max(0, (27.13 * Math.abs(bA)) / (400.0 - Math.abs(bA)));
    double bC =
        Math.signum(bA) * (100.0 / viewingConditions.getFl()) * Math.pow(bCBase, 1.0 / 0.42);
    double rF = rC / viewingConditions.getRgbD()[0];
    double gF = gC / viewingConditions.getRgbD()[1];
    double bF = bC / viewingConditions.getRgbD()[2];

    double[][] matrix = CAM16RGB_TO_XYZ;
    double x = (rF * matrix[0][0]) + (gF * matrix[0][1]) + (bF * matrix[0][2]);
    double y = (rF * matrix[1][0]) + (gF * matrix[1][1]) + (bF * matrix[1][2]);
    double z = (rF * matrix[2][0]) + (gF * matrix[2][1]) + (bF * matrix[2][2]);

    if (returnArray != null) {
      returnArray[0] = x;
      returnArray[1] = y;
      returnArray[2] = z;
      return returnArray;
    } else {
      return new double[] {x, y, z};
    }
  }
}