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Diffstat (limited to 'hct/Cam16.java')
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diff --git a/hct/Cam16.java b/hct/Cam16.java new file mode 100644 index 0000000..36d4895 --- /dev/null +++ b/hct/Cam16.java @@ -0,0 +1,439 @@ +/* + * 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. + */ + 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}; + } + } +} |