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- /*
- * Copyright (C) 2021 Christopher J. Howard
- *
- * This file is part of Antkeeper source code.
- *
- * Antkeeper source code is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Antkeeper source code is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Antkeeper source code. If not, see <http://www.gnu.org/licenses/>.
- */
-
- #ifndef ANTKEEPER_COLOR_XYZ_HPP
- #define ANTKEEPER_COLOR_XYZ_HPP
-
- #include "math/math.hpp"
-
- namespace color {
-
- /**
- * CIE XYZ color space.
- *
- * @see https://en.wikipedia.org/wiki/CIE_1931_color_space
- */
- namespace xyz {
-
- /**
- * Returns the luminance of a CIE XYZ color.
- *
- * @param x CIE XYZ color.
- * @return return Luminance of @p x.
- */
- template <class T>
- constexpr inline T luminance(const math::vector3<T>& x)
- {
- return x[1];
- }
-
- /**
- * Transforms a CIE XYZ color into the CIE xyY color space.
- *
- * @param x CIE XYZ color.
- * @return CIE xyY color.
- */
- template <class T>
- constexpr math::vector3<T> to_xyy(const math::vector3<T>& x)
- {
- const T sum = x[0] + x[1] + x[2];
- return math::vector3<T>{x[0] / sum, x[1] / sum, x[1]}
- }
-
- /**
- * CIE 1931 standard observer color matching function for the X tristimulus value.
- *
- * @param lambda Wavelength of light, in nanometers.
- * @return Matching X tristimulus value.
- *
- * @see match(T)
- */
- template <class T>
- T match_x(T lambda)
- {
- const T t0 = (lambda - T(442.0)) * ((lambda < T(442.0)) ? T(0.0624) : T(0.0374));
- const T t1 = (lambda - T(599.8)) * ((lambda < T(599.8)) ? T(0.0264) : T(0.0323));
- const T t2 = (lambda - T(501.1)) * ((lambda < T(501.1)) ? T(0.0490) : T(0.0382));
-
- const T x0 = T( 0.362) * std::exp(T(-0.5) * t0 * t0);
- const T x1 = T( 1.056) * std::exp(T(-0.5) * t1 * t1);
- const T x2 = T(-0.065) * std::exp(T(-0.5) * t2 * t2);
-
- return x0 + x1 + x2;
- }
-
- /**
- * CIE 1931 standard observer color matching function for the Y tristimulus value.
- *
- * @param lambda Wavelength of light, in nanometers.
- * @return Matching Y tristimulus value.
- *
- * @see match(T)
- */
- template <class T>
- T match_y(T lambda)
- {
- const T t0 = (lambda - T(568.8)) * ((lambda < T(568.8)) ? T(0.0213) : T(0.0247));
- const T t1 = (lambda - T(530.9)) * ((lambda < T(530.9)) ? T(0.0613) : T(0.0322));
-
- const T y0 = T(0.821) * std::exp(T(-0.5) * t0 * t0);
- const T y1 = T(0.286) * std::exp(T(-0.5) * t1 * t1);
-
- return y0 + y1;
- }
-
- /**
- * CIE 1931 standard observer color matching function for the Z tristimulus value.
- *
- * @param lambda Wavelength of light, in nanometers.
- * @return Matching Z tristimulus value.
- *
- * @see match(T)
- */
- template <class T>
- T match_z(T lambda)
- {
- const T t0 = (lambda - T(437.0)) * ((lambda < T(437.0)) ? T(0.0845) : T(0.0278));
- const T t1 = (lambda - T(459.0)) * ((lambda < T(459.0)) ? T(0.0385) : T(0.0725));
-
- const T z0 = T(1.217) * std::exp(T(-0.5) * t0 * t0);
- const T z1 = T(0.681) * std::exp(T(-0.5) * t1 * t1);
-
- return z0 + z1;
- }
-
- /**
- * Fitted piecewise gaussian approximation to the CIE 1931 standard observer color matching function.
- *
- * @param lambda Wavelength of light, in nanometers.
- * @return Matching CIE XYZ color.
- *
- * @see match_x(T)
- * @see match_y(T)
- * @see match_z(T)
- *
- * @see Wyman, C., Sloan, P.J., & Shirley, P. (2013). Simple Analytic Approximations to the CIE XYZ Color Matching Functions.
- */
- template <class T>
- math::vector3<T> match(T lambda)
- {
- return math::vector3<T>
- {
- match_x<T>(lambda),
- match_y<T>(lambda),
- match_z<T>(lambda)
- };
- }
-
- } // namespace xyz
- } // namespace color
-
- #endif // ANTKEEPER_COLOR_XYZ_HPP
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