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Luma Key: Key Out Brighter and Darker cut hard at Threshold, as After Effects

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After Effects' Luma Key removes everything darker (or brighter) than Threshold
and ignores Tolerance for those two key types; Tolerance only sets the band of
Key Out Similar / Dissimilar. EffectCraft ramped the matte over Tolerance, so
case 719 (a 50 % grey, Key Out Darker, Threshold 140, Tolerance 20) kept about
80 % of the layer where AE keys it out completely.

Measured in AE 2026 on a vertical grey ramp (cases 812-814): Darker keys up to
level 139.9 and keeps 140.1 (EffectCraft now the same row); Similar keys levels
120.3-160.0; with Edge Thin 1 / Edge Feather 2.5 the matte rises over rows
591-596 (EffectCraft within 0.2 of AE's alpha there). CPU and GPU.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
vangel76
2026-10-19 16:15:02 +02:00
co-authored by Claude Opus 5.5
parent dc9f15ada1
commit 39bd0efac2
3 changed files with 65 additions and 49 deletions
Download Patch File Download Diff File Expand all files Collapse all files
crates/effects/src/keying.rs
+59 -34
View File
@@ -135,46 +135,23 @@ fn color_key(ctx: &EffectCtx, mut b: Buf) -> Buf {
// ---- Luma Key ----
/// Luma Key as After Effects 2026 keys a grey ramp (cases 812-814, 719): Key Out Brighter and
/// Darker cut hard at Threshold and ignore Tolerance; Key Out Similar removes, and Dissimilar
/// keeps, a hard band of Threshold ± Tolerance (levels of 255). Edge Thin and Edge Feather
/// then soften the cut.
fn luma_key(ctx: &EffectCtx, mut b: Buf) -> Buf {
let kind = ctx.params.e("keyType");
let thr = ctx.params.f("threshold") as f32 / 255.0;
let tol = ctx.params.f("tolerance") as f32 / 255.0;
let m = matte_of(&b.img, |c, _| {
let l = luminance(c[0], c[1], c[2]);
match kind {
0 => {
if tol > 0.0 {
((thr + tol - l) / tol).clamp(0.0, 1.0)
} else if l > thr {
0.0
} else {
1.0
}
}
2 => {
if (l - thr).abs() <= tol {
0.0
} else {
1.0
}
}
3 => {
if (l - thr).abs() <= tol {
1.0
} else {
0.0
}
}
_ => {
if tol > 0.0 {
((l - (thr - tol)) / tol).clamp(0.0, 1.0)
} else if l < thr {
0.0
} else {
1.0
}
}
}
let keep = match kind {
0 => l <= thr,
2 => (l - thr).abs() > tol,
3 => (l - thr).abs() <= tol,
_ => l >= thr,
};
if keep { 1.0 } else { 0.0 }
});
let m = thin_feather(m, ctx.params.f("edgeThin") * b.scale, ctx.params.f("edgeFeather") * b.scale);
apply_matte(&mut b.img, &m, 0);
@@ -802,6 +779,54 @@ mod tests {
assert_eq!(out.get(1, 0)[3], 1.0);
}
/// After Effects 2026 (cases 812-814): Luma Key on a vertical black-to-white ramp (row y
/// has level (y + 0.5) / 1080 × 255), Threshold 140, Tolerance 20. EffectCraft ramped the
/// matte over the tolerance (case 719: a 50 % grey kept 80 % of its alpha where AE keys it
/// out).
#[test]
fn luma_key_matches_after_effects() {
let ramp = || {
let mut img = Image::new(1, 1080);
for y in 0..1080 {
let v = (y as f32 + 0.5) / 1080.0;
img.set(0, y, [v, v, v, 1.0]);
}
img
};
let key = |kind: u32, thin: f64, feather: f64| {
let set =
[("keyType", Value::Enum(kind)), ("threshold", num(140.0)), ("tolerance", num(20.0)), ("edgeThin", num(thin)), ("edgeFeather", num(feather))];
let o = run("ec.key.luma", &set, ramp());
(0..1080).map(|y| o.get(0, y)[3]).collect::<Vec<f32>>()
};
// Key Out Darker (AE 2 = EffectCraft 1): keyed up to row 592, kept from 593.
let d = key(1, 0.0, 0.0);
assert!(d[..593].iter().all(|a| *a == 0.0) && d[593..].iter().all(|a| *a == 1.0), "{:?}", &d[588..598]);
// Key Out Similar: AE keys rows 509..=677 (levels 120.3..160.0) and keeps the rest; the
// rows at the band's ends sit within 0.1 level of 120 / 160, so they may go either way.
let s = key(2, 0.0, 0.0);
assert!(
(0..1080).filter(|y| !(507..=510).contains(y) && !(676..=679).contains(y)).all(|y| (s[y] == 0.0) == (509..=677).contains(&y)),
"{:?} {:?}",
&s[505..512],
&s[674..681]
);
// Key Out Brighter and Dissimilar are the complements.
let b = key(0, 0.0, 0.0);
assert!(b[595] == 0.0 && b[590] == 1.0);
let ds = key(3, 0.0, 0.0);
assert!(ds[600] == 1.0 && ds[400] == 0.0 && ds[700] == 0.0);
// A 50 % grey at Darker 140 / 20 is keyed out entirely (case 719).
let o =
run("ec.key.luma", &[("keyType", Value::Enum(1)), ("threshold", num(140.0)), ("tolerance", num(20.0))], Image::filled(2, 2, [0.5, 0.5, 0.5, 1.0]));
assert_eq!(o.get(0, 0)[3], 0.0);
// Edge Thin 1, Edge Feather 2.5 (case 814): AE's alpha rises over rows 591..596.
let f = key(1, 1.0, 2.5);
for (y, ae) in [(590, 0.0), (591, 0.026), (592, 0.139), (593, 0.357), (594, 0.635), (595, 0.868), (596, 0.97), (597, 1.0)] {
assert!((f[y] - ae).abs() < 0.2, "row {y}: {} vs AE {ae}", f[y]);
}
}
#[test]
fn extract_keeps_range() {
let mut img = Image::new(3, 1);
crates/gpu/src/shaders/fx_key.wgsl
+4 -14
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@@ -199,23 +199,13 @@ fn fxk_point(@builtin(global_invocation_id) gid: vec3<u32>) {
let thr = f0.x;
let tol = f0.y;
var m: f32;
// As effects::keying::luma_key: Brighter / Darker cut hard at the threshold
// (Tolerance only shapes Similar / Dissimilar), as After Effects.
switch u0.y {
case 0u: {
if (tol > 0.0) {
m = clamp((thr + tol - l) / tol, 0.0, 1.0);
} else {
m = select(1.0, 0.0, l > thr);
}
}
case 0u: { m = select(1.0, 0.0, l > thr); }
case 2u: { m = select(1.0, 0.0, abs(l - thr) <= tol); }
case 3u: { m = select(0.0, 1.0, abs(l - thr) <= tol); }
default: {
if (tol > 0.0) {
m = clamp((l - (thr - tol)) / tol, 0.0, 1.0);
} else {
m = select(1.0, 0.0, l < thr);
}
}
default: { m = select(1.0, 0.0, l < thr); }
}
o = vec4<f32>(m);
}
docs/effects-parity.md
+2 -1
View File
@@ -38,7 +38,7 @@ corpus compares renders, each effect is assumed to differ somewhere, and users k
| Keying | 12 | 12 | Key Cleaner approximated; #533 (wire-removal Frame Offset) is closed |
| Matte | 6 | 4 | Mocha shape reads our documented JSON, not Mocha's format |
| Noise & Grain | 13 | 12 | Curl Noise (#463); Match Grain on the CPU |
| Obsolete | 9 | 9 | — |
| Obsolete | 9 | 9 | Luma Key matches After Effects 2026 on a grey ramp (hard cut, Tolerance only for Similar / Dissimilar) |
| Paint | 1 | 0 | Tablet pressure not read ([hardware-parity.md](hardware-parity.md)) |
| Perspective | 10 | 9 | Chromatic Aberrations pan/tilt crash (#580) |
| Simulation | 18 | 18 | Particle Playground lacks Particle Exploder, text particles, ephemeral mapper; CC Particle World camera fixed (#397) |
@@ -68,6 +68,7 @@ the GPU is performance, not parity.
| 2026-10-19 | minor | Black & White's Tint keeps the gray's luminosity (Color blend), measured against After Effects 2026 renders (CPU and GPU) |
| 2026-10-19 | minor | Levels: "Off for 32 bpc Color" no longer clips in 32 bpc projects, unclipped values extrapolate below Output Black; Levels (Individual Controls) applies the channel controls before the RGB ones, measured against After Effects 2026 (CPU and GPU) |
| 2026-10-19 | minor | Brightness & Contrast: negative Brightness / Contrast are the inverse curves of the positive ones (Brightness −40: 20/255 → 6/255 off After Effects 2026), CPU and GPU |
| 2026-10-19 | minor | Luma Key: Key Out Brighter / Darker cut hard at Threshold, measured against After Effects 2026 renders of a ramp (CPU and GPU) |
| 2026-10-18 | minor | Tint uses Rec. 601 luminance weights, measured against After Effects 2026 renders of red, green, blue and grey solids (CPU and GPU) |
| 2026-10-18 | minor | Exposure converts to linear light with a pure 2.2 power curve, as measured in After Effects (Offset 0.0005 / 0.002 / 0.02 / 0.1 on black: 8 / 15 / 43 / 90), not the piecewise sRGB curve; its sliders take After Effects' ranges (Exposure −100..100, slider −4..4; Offset −2..2, slider −0.5..0.5; Gamma Correction 0.1..10) |
| 2026-10-12 | minor | Parameters 3,014 to 3,017 (effects.md); #303, #514, #526, #533–#536 marked closed instead of pending |