color_space.hpp

// Copyright Take Vos 2021.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "../rapid/numeric_array.hpp"
#include "../geometry/matrix.hpp"
#include "../geometry/scale.hpp"
 
namespace tt {
 
[[nodiscard]] constexpr matrix3
color_primaries_to_RGBtoXYZ(float wx, float wy, float rx, float ry, float gx, float gy, float bx, float by) noexcept
{
    ttlet w = vector3{wx, wy, 1.0f - wx - wy};
    ttlet r = vector3{rx, ry, 1.0f - rx - ry};
    ttlet g = vector3{gx, gy, 1.0f - gx - gy};
    ttlet b = vector3{bx, by, 1.0f - bx - by};
 
    // Calculate white point's tristimulus values from coordinates
    ttlet W = vector3{1.0f * (w.x() / w.y()), 1.0f, 1.0f * (w.z() / w.y())};
 
    // C is the chromaticity matrix.
    ttlet C = matrix3{r, g, b};
 
    // solve tristimulus sums.
    ttlet S = scale3{~C * W};
 
    return C * S;
}
 
} // namespace tt