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- /*
- * Copyright (C) 2023 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_RGB_HPP
- #define ANTKEEPER_COLOR_RGB_HPP
-
- #include "color/cat.hpp"
- #include "math/matrix.hpp"
- #include "math/vector.hpp"
-
- namespace color {
-
- /// RGB color spaces.
- namespace rgb {
-
- /**
- * Constructs a matrix which transforms an RGB color into a CIE XYZ color.
- *
- * @param r CIE xy chromaticity coordinates of the red primary.
- * @param g CIE xy chromaticity coordinates of the green primary.
- * @param b CIE xy chromaticity coordinates of the blue primary.
- * @param w CIE xy chromaticity coordinates of the white point.
- *
- * @return Matrix which transforms an RGB color into a CIE XYZ color.
- *
- * @see https://www.ryanjuckett.com/rgb-color-space-conversion/
- * @see https://mina86.com/2019/srgb-xyz-matrix/
- */
- template <class T>
- constexpr math::matrix<T, 3, 3> to_xyz(const math::vector2<T>& r, const math::vector2<T>& g, const math::vector2<T>& b, const math::vector2<T>& w)
- {
- const math::matrix<T, 3, 3> m =
- {
- r[0], r[1], T{1} - (r[0] + r[1]),
- g[0], g[1], T{1} - (g[0] + g[1]),
- b[0], b[1], T{1} - (b[0] + b[1])
- };
-
- const math::vector3<T> scale = math::inverse(m) * math::vector3<T>{w[0] / w[1], T{1}, (T{1} - (w[0] + w[1])) / w[1]};
-
- return math::matrix<T, 3, 3>
- {
- m[0][0] * scale[0], m[0][1] * scale[0], m[0][2] * scale[0],
- m[1][0] * scale[1], m[1][1] * scale[1], m[1][2] * scale[1],
- m[2][0] * scale[2], m[2][1] * scale[2], m[2][2] * scale[2],
- };
- }
-
- /**
- * RGB color space.
- */
- template <class T>
- struct color_space
- {
- /// Transfer function function pointer type.
- typedef math::vector3<T> (*transfer_function_type)(const math::vector3<T>&);
-
- /// CIE xy chromaticity coordinates of the red primary.
- const math::vector2<T> r;
-
- /// CIE xy chromaticity coordinates of the green primary.
- const math::vector2<T> g;
-
- /// CIE xy chromaticity coordinates of the blue primary.
- const math::vector2<T> b;
-
- /// CIE xy chromaticity coordinates of the white point.
- const math::vector2<T> w;
-
- /// Function pointer to the electro-optical transfer function.
- const transfer_function_type eotf;
-
- /// Function pointer to the inverse electro-optical transfer function.
- const transfer_function_type inverse_eotf;
-
- /// Matrix which transforms an RGB color to a CIE XYZ color.
- const math::matrix3x3<T> to_xyz;
-
- /// Matrix which transforms a CIE XYZ color to an RGB color.
- const math::matrix3x3<T> from_xyz;
-
- /// Vector which gives the luminance of an RGB color via dot product.
- const math::vector3<T> to_y;
-
- /**
- * Constructs an RGB color space.
- *
- * @param r CIE xy chromaticity coordinates of the red primary.
- * @param g CIE xy chromaticity coordinates of the green primary.
- * @param b CIE xy chromaticity coordinates of the blue primary.
- * @param w CIE xy chromaticity coordinates of the white point.
- */
- constexpr color_space(const math::vector2<T>& r, const math::vector2<T>& g, const math::vector2<T>& b, const math::vector2<T>& w, transfer_function_type eotf, transfer_function_type inverse_eotf);
-
- /**
- * Measures the luminance of a linear RGB color.
- *
- * @param x Linear RGB color.
- * @return return Luminance of @p x.
- */
- constexpr T luminance(const math::vector3<T>& x) const;
- };
-
- template <class T>
- constexpr color_space<T>::color_space(const math::vector2<T>& r, const math::vector2<T>& g, const math::vector2<T>& b, const math::vector2<T>& w, transfer_function_type eotf, transfer_function_type inverse_eotf):
- r(r),
- g(g),
- b(b),
- w(w),
- eotf(eotf),
- inverse_eotf(inverse_eotf),
- to_xyz(color::rgb::to_xyz<T>(r, g, b, w)),
- from_xyz(math::inverse(to_xyz)),
- to_y{to_xyz[0][1], to_xyz[1][1], to_xyz[2][1]}
- {}
-
- template <class T>
- constexpr T color_space<T>::luminance(const math::vector3<T>& x) const
- {
- return math::dot(x, to_y);
- }
-
- /**
- * Constructs a matrix which transforms a color from one RGB color space to another RGB color space.
- *
- * @param s0 Source color space.
- * @param s1 Destination color space.
- * @param cone_response Chromatic adaptation transform cone response matrix.
- *
- * @return Color space transformation matrix.
- */
- template <class T>
- constexpr math::matrix3x3<T> to_rgb(const color_space<T>& s0, const color_space<T>& s1, const math::matrix3x3<T>& cone_response = color::cat::bradford<T>)
- {
- return s1.from_xyz * color::cat::matrix(s0.w, s1.w, cone_response) * s0.to_xyz;
- }
-
- } // namespace rgb
- } // namespace color
-
- #endif // ANTKEEPER_COLOR_RGB_HPP
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