💿🐜 Antkeeper source code
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147 lines
3.8 KiB
147 lines
3.8 KiB
/*
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* Copyright (C) 2023 Christopher J. Howard
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*
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* This file is part of Antkeeper source code.
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*
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* Antkeeper source code is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Antkeeper source code is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Antkeeper source code. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef ANTKEEPER_COLOR_XYZ_HPP
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#define ANTKEEPER_COLOR_XYZ_HPP
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#include "math/vector.hpp"
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namespace color {
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/**
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* CIE XYZ color space.
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*
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* @see https://en.wikipedia.org/wiki/CIE_1931_color_space
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*/
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namespace xyz {
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/**
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* Returns the luminance of a CIE XYZ color.
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*
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* @param x CIE XYZ color.
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* @return return Luminance of @p x.
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*/
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template <class T>
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inline constexpr T luminance(const math::vector3<T>& x)
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{
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return x[1];
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}
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/**
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* Transforms a CIE XYZ color into the CIE xyY color space.
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*
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* @param x CIE XYZ color.
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* @return CIE xyY color.
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*/
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template <class T>
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constexpr math::vector3<T> to_xyy(const math::vector3<T>& x)
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{
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const T sum = x[0] + x[1] + x[2];
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return math::vector3<T>{x[0] / sum, x[1] / sum, x[1]};
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}
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/**
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* CIE 1931 standard observer color matching function for the X tristimulus value.
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*
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* @param lambda Wavelength of light, in nanometers.
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* @return Matching X tristimulus value.
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*
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* @see match(T)
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*/
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template <class T>
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T match_x(T lambda)
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{
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const T t0 = (lambda - T(442.0)) * ((lambda < T(442.0)) ? T(0.0624) : T(0.0374));
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const T t1 = (lambda - T(599.8)) * ((lambda < T(599.8)) ? T(0.0264) : T(0.0323));
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const T t2 = (lambda - T(501.1)) * ((lambda < T(501.1)) ? T(0.0490) : T(0.0382));
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const T x0 = T( 0.362) * std::exp(T(-0.5) * t0 * t0);
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const T x1 = T( 1.056) * std::exp(T(-0.5) * t1 * t1);
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const T x2 = T(-0.065) * std::exp(T(-0.5) * t2 * t2);
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return x0 + x1 + x2;
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}
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/**
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* CIE 1931 standard observer color matching function for the Y tristimulus value.
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*
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* @param lambda Wavelength of light, in nanometers.
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* @return Matching Y tristimulus value.
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*
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* @see match(T)
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*/
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template <class T>
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T match_y(T lambda)
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{
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const T t0 = (lambda - T(568.8)) * ((lambda < T(568.8)) ? T(0.0213) : T(0.0247));
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const T t1 = (lambda - T(530.9)) * ((lambda < T(530.9)) ? T(0.0613) : T(0.0322));
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const T y0 = T(0.821) * std::exp(T(-0.5) * t0 * t0);
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const T y1 = T(0.286) * std::exp(T(-0.5) * t1 * t1);
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return y0 + y1;
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}
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/**
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* CIE 1931 standard observer color matching function for the Z tristimulus value.
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*
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* @param lambda Wavelength of light, in nanometers.
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* @return Matching Z tristimulus value.
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*
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* @see match(T)
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*/
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template <class T>
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T match_z(T lambda)
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{
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const T t0 = (lambda - T(437.0)) * ((lambda < T(437.0)) ? T(0.0845) : T(0.0278));
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const T t1 = (lambda - T(459.0)) * ((lambda < T(459.0)) ? T(0.0385) : T(0.0725));
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const T z0 = T(1.217) * std::exp(T(-0.5) * t0 * t0);
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const T z1 = T(0.681) * std::exp(T(-0.5) * t1 * t1);
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return z0 + z1;
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}
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/**
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* Fitted piecewise gaussian approximation to the CIE 1931 standard observer color matching function.
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*
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* @param lambda Wavelength of light, in nanometers.
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* @return Matching CIE XYZ color.
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*
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* @see match_x(T)
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* @see match_y(T)
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* @see match_z(T)
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*
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* @see Wyman, C., Sloan, P.J., & Shirley, P. (2013). Simple Analytic Approximations to the CIE XYZ Color Matching Functions.
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*/
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template <class T>
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math::vector3<T> match(T lambda)
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{
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return math::vector3<T>
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{
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match_x<T>(lambda),
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match_y<T>(lambda),
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match_z<T>(lambda)
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};
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}
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} // namespace xyz
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} // namespace color
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#endif // ANTKEEPER_COLOR_XYZ_HPP
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