hct/ViewingConditions.java - platform/external/libmonet - Git at Google

 /*
  * 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 com.google.ux.material.libmonet.utils.ColorUtils;
 import com.google.ux.material.libmonet.utils.MathUtils;

 /**
  * 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)
  *
  * <p>This class caches intermediate values of the CAM16 conversion process that depend only on
  * viewing conditions, enabling speed ups.
  */
 public final class ViewingConditions {
   /** sRGB-like viewing conditions. */
   public static final ViewingConditions DEFAULT =
       ViewingConditions.defaultWithBackgroundLstar(50.0);

   private final double aw;
   private final double nbb;
   private final double ncb;
   private final double c;
   private final double nc;
   private final double n;
   private final double[] rgbD;
   private final double fl;
   private final double flRoot;
   private final double z;

   public double getAw() {
     return aw;
   }

   public double getN() {
     return n;
   }

   public double getNbb() {
     return nbb;
   }

   double getNcb() {
     return ncb;
   }

   double getC() {
     return c;
   }

   double getNc() {
     return nc;
   }

   public double[] getRgbD() {
     return rgbD;
   }

   double getFl() {
     return fl;
   }

   public double getFlRoot() {
     return flRoot;
   }

   double getZ() {
     return z;
   }

   /**
    * Create ViewingConditions from a simple, physically relevant, set of parameters.
    *
    * @param whitePoint White point, measured in the XYZ color space. default = D65, or sunny day
    *     afternoon
    * @param adaptingLuminance The luminance of the adapting field. Informally, how bright it is in
    *     the room where the color is viewed. Can be calculated from lux by multiplying lux by
    *     0.0586. default = 11.72, or 200 lux.
    * @param backgroundLstar The lightness of the area surrounding the color. measured by L* in
    *     L*a*b*. default = 50.0
    * @param surround A general description of the lighting surrounding the color. 0 is pitch dark,
    *     like watching a movie in a theater. 1.0 is a dimly light room, like watching TV at home at
    *     night. 2.0 means there is no difference between the lighting on the color and around it.
    *     default = 2.0
    * @param discountingIlluminant Whether the eye accounts for the tint of the ambient lighting,
    *     such as knowing an apple is still red in green light. default = false, the eye does not
    *     perform this process on self-luminous objects like displays.
    */
   public static ViewingConditions make(
       double[] whitePoint,
       double adaptingLuminance,
       double backgroundLstar,
       double surround,
       boolean discountingIlluminant) {
     // A background of pure black is non-physical and leads to infinities that represent the idea
     // that any color viewed in pure black can't be seen.
     backgroundLstar = Math.max(0.1, backgroundLstar);
     // Transform white point XYZ to 'cone'/'rgb' responses
     double[][] matrix = Cam16.XYZ_TO_CAM16RGB;
     double[] xyz = whitePoint;
     double rW = (xyz[0] * matrix[0][0]) + (xyz[1] * matrix[0][1]) + (xyz[2] * matrix[0][2]);
     double gW = (xyz[0] * matrix[1][0]) + (xyz[1] * matrix[1][1]) + (xyz[2] * matrix[1][2]);
     double bW = (xyz[0] * matrix[2][0]) + (xyz[1] * matrix[2][1]) + (xyz[2] * matrix[2][2]);
     double f = 0.8 + (surround / 10.0);
     double c =
         (f >= 0.9)
             ? MathUtils.lerp(0.59, 0.69, ((f - 0.9) * 10.0))
             : MathUtils.lerp(0.525, 0.59, ((f - 0.8) * 10.0));
     double d =
         discountingIlluminant
             ? 1.0
             : f * (1.0 - ((1.0 / 3.6) * Math.exp((-adaptingLuminance - 42.0) / 92.0)));
     d = MathUtils.clampDouble(0.0, 1.0, d);
     double nc = f;
     double[] rgbD =
         new double[] {
           d * (100.0 / rW) + 1.0 - d, d * (100.0 / gW) + 1.0 - d, d * (100.0 / bW) + 1.0 - d
         };
     double k = 1.0 / (5.0 * adaptingLuminance + 1.0);
     double k4 = k * k * k * k;
     double k4F = 1.0 - k4;
     double fl = (k4 * adaptingLuminance) + (0.1 * k4F * k4F * Math.cbrt(5.0 * adaptingLuminance));
     double n = (ColorUtils.yFromLstar(backgroundLstar) / whitePoint[1]);
     double z = 1.48 + Math.sqrt(n);
     double nbb = 0.725 / Math.pow(n, 0.2);
     double ncb = nbb;
     double[] rgbAFactors =
         new double[] {
           Math.pow(fl * rgbD[0] * rW / 100.0, 0.42),
           Math.pow(fl * rgbD[1] * gW / 100.0, 0.42),
           Math.pow(fl * rgbD[2] * bW / 100.0, 0.42)
         };

     double[] rgbA =
         new double[] {
           (400.0 * rgbAFactors[0]) / (rgbAFactors[0] + 27.13),
           (400.0 * rgbAFactors[1]) / (rgbAFactors[1] + 27.13),
           (400.0 * rgbAFactors[2]) / (rgbAFactors[2] + 27.13)
         };

     double aw = ((2.0 * rgbA[0]) + rgbA[1] + (0.05 * rgbA[2])) * nbb;
     return new ViewingConditions(n, aw, nbb, ncb, c, nc, rgbD, fl, Math.pow(fl, 0.25), z);
   }

   /**
    * Create sRGB-like viewing conditions with a custom background lstar.
    *
    * <p>Default viewing conditions have a lstar of 50, midgray.
    */
   public static ViewingConditions defaultWithBackgroundLstar(double lstar) {
     return ViewingConditions.make(
         ColorUtils.whitePointD65(),
         (200.0 / Math.PI * ColorUtils.yFromLstar(50.0) / 100.f),
         lstar,
         2.0,
         false);
   }

   /**
    * Parameters are intermediate values of the CAM16 conversion process. Their names are shorthand
    * for technical color science terminology, this class would not benefit from documenting them
    * individually. A brief overview is available in the CAM16 specification, and a complete overview
    * requires a color science textbook, such as Fairchild's Color Appearance Models.
    */
   private ViewingConditions(
       double n,
       double aw,
       double nbb,
       double ncb,
       double c,
       double nc,
       double[] rgbD,
       double fl,
       double flRoot,
       double z) {
     this.n = n;
     this.aw = aw;
     this.nbb = nbb;
     this.ncb = ncb;
     this.c = c;
     this.nc = nc;
     this.rgbD = rgbD;
     this.fl = fl;
     this.flRoot = flRoot;
     this.z = z;
   }
 }
	/*
	* 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 com.google.ux.material.libmonet.utils.ColorUtils;
	import com.google.ux.material.libmonet.utils.MathUtils;

	/**
	* 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)
	*
	* <p>This class caches intermediate values of the CAM16 conversion process that depend only on
	* viewing conditions, enabling speed ups.
	*/
	public final class ViewingConditions {
	/** sRGB-like viewing conditions. */
	public static final ViewingConditions DEFAULT =
	ViewingConditions.defaultWithBackgroundLstar(50.0);

	private final double aw;
	private final double nbb;
	private final double ncb;
	private final double c;
	private final double nc;
	private final double n;
	private final double[] rgbD;
	private final double fl;
	private final double flRoot;
	private final double z;

	public double getAw() {
	return aw;
	}

	public double getN() {
	return n;
	}

	public double getNbb() {
	return nbb;
	}

	double getNcb() {
	return ncb;
	}

	double getC() {
	return c;
	}

	double getNc() {
	return nc;
	}

	public double[] getRgbD() {
	return rgbD;
	}

	double getFl() {
	return fl;
	}

	public double getFlRoot() {
	return flRoot;
	}

	double getZ() {
	return z;
	}

	/**
	* Create ViewingConditions from a simple, physically relevant, set of parameters.
	*
	* @param whitePoint White point, measured in the XYZ color space. default = D65, or sunny day
	* afternoon
	* @param adaptingLuminance The luminance of the adapting field. Informally, how bright it is in
	* the room where the color is viewed. Can be calculated from lux by multiplying lux by
	* 0.0586. default = 11.72, or 200 lux.
	* @param backgroundLstar The lightness of the area surrounding the color. measured by L* in
	* Lab*. default = 50.0
	* @param surround A general description of the lighting surrounding the color. 0 is pitch dark,
	* like watching a movie in a theater. 1.0 is a dimly light room, like watching TV at home at
	* night. 2.0 means there is no difference between the lighting on the color and around it.
	* default = 2.0
	* @param discountingIlluminant Whether the eye accounts for the tint of the ambient lighting,
	* such as knowing an apple is still red in green light. default = false, the eye does not
	* perform this process on self-luminous objects like displays.
	*/
	public static ViewingConditions make(
	double[] whitePoint,
	double adaptingLuminance,
	double backgroundLstar,
	double surround,
	boolean discountingIlluminant) {
	// A background of pure black is non-physical and leads to infinities that represent the idea
	// that any color viewed in pure black can't be seen.
	backgroundLstar = Math.max(0.1, backgroundLstar);
	// Transform white point XYZ to 'cone'/'rgb' responses
	double[][] matrix = Cam16.XYZ_TO_CAM16RGB;
	double[] xyz = whitePoint;
	double rW = (xyz[0] * matrix[0][0]) + (xyz[1] * matrix[0][1]) + (xyz[2] * matrix[0][2]);
	double gW = (xyz[0] * matrix[1][0]) + (xyz[1] * matrix[1][1]) + (xyz[2] * matrix[1][2]);
	double bW = (xyz[0] * matrix[2][0]) + (xyz[1] * matrix[2][1]) + (xyz[2] * matrix[2][2]);
	double f = 0.8 + (surround / 10.0);
	double c =
	(f >= 0.9)
	? MathUtils.lerp(0.59, 0.69, ((f - 0.9) * 10.0))
	: MathUtils.lerp(0.525, 0.59, ((f - 0.8) * 10.0));
	double d =
	discountingIlluminant
	? 1.0
	: f * (1.0 - ((1.0 / 3.6) * Math.exp((-adaptingLuminance - 42.0) / 92.0)));
	d = MathUtils.clampDouble(0.0, 1.0, d);
	double nc = f;
	double[] rgbD =
	new double[] {
	d * (100.0 / rW) + 1.0 - d, d * (100.0 / gW) + 1.0 - d, d * (100.0 / bW) + 1.0 - d
	};
	double k = 1.0 / (5.0 * adaptingLuminance + 1.0);
	double k4 = k * k * k * k;
	double k4F = 1.0 - k4;
	double fl = (k4 * adaptingLuminance) + (0.1 * k4F * k4F * Math.cbrt(5.0 * adaptingLuminance));
	double n = (ColorUtils.yFromLstar(backgroundLstar) / whitePoint[1]);
	double z = 1.48 + Math.sqrt(n);
	double nbb = 0.725 / Math.pow(n, 0.2);
	double ncb = nbb;
	double[] rgbAFactors =
	new double[] {
	Math.pow(fl * rgbD[0] * rW / 100.0, 0.42),
	Math.pow(fl * rgbD[1] * gW / 100.0, 0.42),
	Math.pow(fl * rgbD[2] * bW / 100.0, 0.42)
	};

	double[] rgbA =
	new double[] {
	(400.0 * rgbAFactors[0]) / (rgbAFactors[0] + 27.13),
	(400.0 * rgbAFactors[1]) / (rgbAFactors[1] + 27.13),
	(400.0 * rgbAFactors[2]) / (rgbAFactors[2] + 27.13)
	};

	double aw = ((2.0 * rgbA[0]) + rgbA[1] + (0.05 * rgbA[2])) * nbb;
	return new ViewingConditions(n, aw, nbb, ncb, c, nc, rgbD, fl, Math.pow(fl, 0.25), z);
	}

	/**
	* Create sRGB-like viewing conditions with a custom background lstar.
	*
	* <p>Default viewing conditions have a lstar of 50, midgray.
	*/
	public static ViewingConditions defaultWithBackgroundLstar(double lstar) {
	return ViewingConditions.make(
	ColorUtils.whitePointD65(),
	(200.0 / Math.PI * ColorUtils.yFromLstar(50.0) / 100.f),
	lstar,
	2.0,
	false);
	}

	/**
	* Parameters are intermediate values of the CAM16 conversion process. Their names are shorthand
	* for technical color science terminology, this class would not benefit from documenting them
	* individually. A brief overview is available in the CAM16 specification, and a complete overview
	* requires a color science textbook, such as Fairchild's Color Appearance Models.
	*/
	private ViewingConditions(
	double n,
	double aw,
	double nbb,
	double ncb,
	double c,
	double nc,
	double[] rgbD,
	double fl,
	double flRoot,
	double z) {
	this.n = n;
	this.aw = aw;
	this.nbb = nbb;
	this.ncb = ncb;
	this.c = c;
	this.nc = nc;
	this.rgbD = rgbD;
	this.fl = fl;
	this.flRoot = flRoot;
	this.z = z;
	}
	}