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Code Issues 144 Wiki Activity

Add a white balance to the tonemapping

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Hirek
2026-10-27 01:40:19 +01:00
parent 82d3842495
commit ac0b4e5f15
13 changed files with 122 additions and 6 deletions
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57
rendering/common/exposure.cpp
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@@ -24,6 +24,51 @@ std::size_t const BLOOM_LEVELS{6};
int const BLOOM_MIN_SIZE{8};
// soft knee of the threshold, a fraction of it
float const BLOOM_KNEE{0.5f};
// colour temperature of the white the image is balanced to: the white of the display (d65 is the daylight of about 6500 K)
float const WHITE_BALANCE_REFERENCE{6500.f};
// distance off the daylight locus (duv, cie 1960 ucs) of the tint at its ends (-1, 1)
float const WHITE_BALANCE_TINT_DUV{0.02f};
// chromaticity (cie xy) of the cie daylight of the correlated colour temperature Kelvin; the formula holds for 4000..25000 K
glm::dvec2 daylight_chromaticity(double const Kelvin)
{
auto const t{std::clamp(Kelvin, 4000.0, 25000.0)};
auto const x{t <= 7000.0 ? (-4.6070e9 / (t * t * t) + 2.9678e6 / (t * t) + 0.09911e3 / t + 0.244063)
: (-2.0064e9 / (t * t * t) + 1.9018e6 / (t * t) + 0.24748e3 / t + 0.237040)};
return glm::dvec2{x, -3.0 * x * x + 2.87 * x - 0.275};
}
glm::dvec2 xy_to_uv(glm::dvec2 const &Xy)
{
auto const d{-2.0 * Xy.x + 12.0 * Xy.y + 3.0};
return glm::dvec2{4.0 * Xy.x / d, 6.0 * Xy.y / d};
}
glm::dvec2 uv_to_xy(glm::dvec2 const &Uv)
{
auto const d{2.0 * Uv.x - 8.0 * Uv.y + 4.0};
return glm::dvec2{3.0 * Uv.x / d, 2.0 * Uv.y / d};
}
// cone responses (bradford) of the light of the temperature Kelvin, taken off the daylight locus by Tint: + towards green
// (v grows), so a positive tint takes the green out of the image and makes it magenta
glm::dvec3 white_cone_response(double const Kelvin, double const Tint)
{
auto uv{xy_to_uv(daylight_chromaticity(Kelvin))};
if (Tint != 0.0)
{
auto const along{xy_to_uv(daylight_chromaticity(Kelvin + 100.0)) - xy_to_uv(daylight_chromaticity(Kelvin - 100.0))};
auto normal{glm::normalize(glm::dvec2{-along.y, along.x})};
if (normal.y < 0.0)
normal = -normal;
uv += normal * (Tint * WHITE_BALANCE_TINT_DUV);
}
auto const xy{uv_to_xy(uv)};
glm::dvec3 const xyz{xy.x / xy.y, 1.0, (1.0 - xy.x - xy.y) / xy.y};
return glm::dvec3{0.8951 * xyz.x + 0.2664 * xyz.y - 0.1614 * xyz.z,
-0.7502 * xyz.x + 1.7135 * xyz.y + 0.0367 * xyz.z,
0.0389 * xyz.x - 0.0685 * xyz.y + 1.0296 * xyz.z};
}
} // namespace
@@ -77,6 +122,15 @@ glm::vec4 exposure_settings::tonemap_params(std::size_t const Bloomlevels)
return glm::vec4{bloom, Global.gfx_postfx_autoexposure ? 1.f : 0.f, std::exp2(Global.gfx_postfx_autoexposure_compensation), Bloomlevels > 0 ? 1.f / static_cast<float>(Bloomlevels) : 0.f};
}
glm::vec3 exposure_settings::white_balance()
{
if (!Global.gfx_postfx_whitebalance)
return glm::vec3{0.f};
// von kries: the light of the set temperature becomes the white of the display; the luminance of grey stays
auto const gains{white_cone_response(WHITE_BALANCE_REFERENCE, 0.0) / white_cone_response(Global.gfx_postfx_whitebalance_temperature, Global.gfx_postfx_whitebalance_tint)};
return glm::vec3{gains};
}
void exposure_settings::draw_debug_ui(float const *Readback)
{
ImGui::Checkbox("automatic exposure (gfx.postfx.autoexposure)", &Global.gfx_postfx_autoexposure);
@@ -90,6 +144,9 @@ void exposure_settings::draw_debug_ui(float const *Readback)
ImGui::Checkbox("bloom (gfx.postfx.bloom)", &Global.gfx_postfx_bloom);
ImGui::SliderFloat("bloom intensity", &Global.gfx_postfx_bloom_intensity, 0.f, 0.5f);
ImGui::SliderFloat("bloom threshold", &Global.gfx_postfx_bloom_threshold, 0.f, 10.f);
ImGui::Checkbox("white balance (gfx.postfx.whitebalance)", &Global.gfx_postfx_whitebalance);
ImGui::SliderFloat("temperature K, 6500 = none, more = warmer", &Global.gfx_postfx_whitebalance_temperature, 4000.f, 12000.f, "%.0f");
ImGui::SliderFloat("tint, + magenta, - green", &Global.gfx_postfx_whitebalance_tint, -1.f, 1.f, "%.2f");
}
} // namespace gfx

2
rendering/common/exposure.h
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@@ -37,6 +37,8 @@ struct exposure_settings
static glm::vec4 bloom_params(std::size_t const Level);
// parameters of the tonemapping (postfx_tonemapping.frag), with bloom from a chain of Bloomlevels levels (0: none)
static glm::vec4 tonemap_params(std::size_t const Bloomlevels);
// white balance of the tonemapping (gfx.postfx.whitebalance*): gains of the cone responses (bradford), 0 when off
static glm::vec3 white_balance();
// controls of the debug window; Readback: the adapted luminance, the exposure and the average luminance the gpu worked out
static void draw_debug_ui(float const *Readback);
};