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Replace the 'Luminance' node with a 'Desaturate' node with a better selection of desaturation methods (#4529)

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* Remove the 'Threshold' node's luminance calculation dropdown so it always compares the Rec. 601 luma

* Find the HSL lightness extremes before encoding and drop a stale luminance TODO
This commit is contained in:
Keavon Chambers
2026-09-14 14:34:55 -07:00
committed by GitHub
parent eaadea6593
commit 1940e430dc
7 changed files with 103 additions and 42 deletions
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33
node-graph/libraries/no-std-types/src/color/color_types.rs
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@@ -45,7 +45,6 @@ impl Luminance for RGBA16F {
type LuminanceChannel = f32;
#[inline(always)]
fn luminance(&self) -> f32 {
// TODO: verify this is correct for sRGB
0.2126 * self.red() + 0.7152 * self.green() + 0.0722 * self.blue()
}
}
@@ -541,37 +540,36 @@ impl Color {
}
/// Relative luminance using Rec.709 / sRGB-primary weights, computed on linear-light RGB.
// From https://stackoverflow.com/a/56678483/775283
#[inline(always)]
pub fn luminance_rec_709(&self) -> f32 {
// From https://en.wikipedia.org/wiki/Luma_(video)#Rec._601_luma_versus_Rec._709_luma_coefficients
0.2126 * self.red + 0.7152 * self.green + 0.0722 * self.blue
}
/// Luma using Rec.601 SDTV coefficients.
// From https://en.wikipedia.org/wiki/Luma_(video)#Rec._601_luma_versus_Rec._709_luma_coefficients
#[inline(always)]
pub fn luminance_rec_601(&self) -> f32 {
// From https://en.wikipedia.org/wiki/Luma_(video)#Rec._601_luma_versus_Rec._709_luma_coefficients
0.299 * self.red + 0.587 * self.green + 0.114 * self.blue
}
/// Luma using rounded Rec.601 coefficients (`0.3 / 0.59 / 0.11`), as used by some legacy image processing.
// From https://en.wikipedia.org/wiki/Luma_(video)#Rec._601_luma_versus_Rec._709_luma_coefficients
#[inline(always)]
pub fn luminance_rec_601_rounded(&self) -> f32 {
// From https://en.wikipedia.org/wiki/Luma_(video)#Rec._601_luma_versus_Rec._709_luma_coefficients
0.3 * self.red + 0.59 * self.green + 0.11 * self.blue
}
/// Perceptual lightness (CIE L*) of the Rec.709 luminance, normalized to 0..1.
// From https://stackoverflow.com/a/56678483/775283
/// Perceptual lightness (OkLab L) of the linear-light RGB, 0..1.
#[inline(always)]
pub fn luminance_perceptual(&self) -> f32 {
let luminance = self.luminance_rec_709();
pub fn lightness_oklab(&self) -> f32 {
// From https://bottosson.github.io/posts/oklab/#converting-from-linear-srgb-to-oklab
if luminance <= 0.008856 {
(luminance * 903.3) / 100.
} else {
(luminance.cbrt() * 116. - 16.) / 100.
}
let long = 0.41222147 * self.red + 0.53633254 * self.green + 0.05144599 * self.blue;
let medium = 0.2119035 * self.red + 0.6806995 * self.green + 0.10739696 * self.blue;
let short = 0.08830246 * self.red + 0.28171884 * self.green + 0.6299787 * self.blue;
0.21045426 * long.cbrt() + 0.7936178 * medium.cbrt() - 0.004072047 * short.cbrt()
}
/// Construct an opaque grayscale color where R = G = B = `luminance`.
@@ -1062,6 +1060,15 @@ impl Color {
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn oklab_lightness_spans_black_to_white() {
assert!(Color::BLACK.lightness_oklab().abs() < 1e-4);
assert!((Color::WHITE.lightness_oklab() - 1.).abs() < 1e-4);
// A gray keeps L at the cube root of its linear value, since the three cone responses sum to it
assert!((Color::from_luminance(0.18).lightness_oklab() - 0.18_f32.cbrt()).abs() < 1e-3);
}
#[test]
fn hsl_roundtrip() {
for (red, green, blue) in [