/*
* 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 .
*/
#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
constexpr math::matrix to_xyz(const math::vector2& r, const math::vector2& g, const math::vector2& b, const math::vector2& w)
{
const math::matrix 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 scale = math::inverse(m) * math::vector3{w[0] / w[1], T{1}, (T{1} - (w[0] + w[1])) / w[1]};
return math::matrix
{
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
struct color_space
{
/// Transfer function function pointer type.
typedef math::vector3 (*transfer_function_type)(const math::vector3&);
/// CIE xy chromaticity coordinates of the red primary.
const math::vector2 r;
/// CIE xy chromaticity coordinates of the green primary.
const math::vector2 g;
/// CIE xy chromaticity coordinates of the blue primary.
const math::vector2 b;
/// CIE xy chromaticity coordinates of the white point.
const math::vector2 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 to_xyz;
/// Matrix which transforms a CIE XYZ color to an RGB color.
const math::matrix3x3 from_xyz;
/// Vector which gives the luminance of an RGB color via dot product.
const math::vector3 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& r, const math::vector2& g, const math::vector2& b, const math::vector2& 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& x) const;
};
template
constexpr color_space::color_space(const math::vector2& r, const math::vector2& g, const math::vector2& b, const math::vector2& 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(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
constexpr T color_space::luminance(const math::vector3& 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
constexpr math::matrix3x3 to_rgb(const color_space& s0, const color_space& s1, const math::matrix3x3& cone_response = color::cat::bradford)
{
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