Fractal / Turbulent Noise: lattice cells are two thirds of Scale, as After Effects

After Effects 2026 draws Fractal Noise's Block noise at Scale 100 and
Complexity 1 in cells of 66.67 px (the value changes every 66.67 px along a
row), not 100 px; Soft Linear noise has the matching correlation length.
EffectCraft's lattice is now Scale x 2/3 px (NOISE_CELL), CPU and GPU. Case
904 E03 (Soft Linear, Complexity 4, Scale 100): the noise's autocorrelation
at 32 px was 0.68 (AE 0.41), now 0.54; pixel values cannot match (other
seeds). Still open: AE's noise spreads about 20 % wider around its mean (std
48 vs 40/255 in E03). Existing projects and the Backgrounds presets with
Fractal Noise get finer noise (two thirds of the former cell size).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/effects/src/lib.rs

@@ -103,7 +103,7 @@ pub use transition::place_layer;
 // effectcraft-gpu fx_noise.
 pub use keying2::{InnerOuterPlan, inner_outer_plan};
 pub use noise::remove_grain_level;
-pub use noise3::{FractalGpu, fractal_gpu};
+pub use noise3::{FractalGpu, NOISE_CELL, fractal_gpu};
 pub use stylize3::{BumpLight, bump_layer_id};
 pub use textfx::{TextLayer, text_layer};
 pub use time_fx::{PixelMotion, TimewarpPlan, TwStep, pmb_plan, posterized_time, time_frames, timewarp_crop, timewarp_plan};

crates/effects/src/noise3.rs

@@ -60,6 +60,11 @@ pub const BLEND_NORMAL: u32 = 1;
 /// Index of "Soft Linear" in [`NOISE_TYPES`] (the default, and the GPU path's interpolation).
 pub const NOISE_SOFT_LINEAR: u32 = 2;
 
+/// Lattice cell of Fractal / Turbulent Noise in pixels per percent of Scale: After Effects 2026
+/// draws Block noise at Scale 100 in 66.67 px cells (and Soft Linear noise has the matching
+/// correlation length), not 100 px.
+pub const NOISE_CELL: f64 = 2.0 / 3.0;
+
 fn spec(id: &'static str, name: &'static str, params: Vec<ParamSpec>, render: crate::RenderFn) -> EffectSpec {
     EffectSpec { id, name, category: "Noise & Grain", params, render, gpu: false, float: true }
 }
@@ -236,7 +241,7 @@ impl Fractal {
             overflow: pr.e("overflow"),
             invert: pr.b("invert"),
             rot: rot.sin_cos(),
-            size: [(sw * b.scale).max(1.0) as f32, (sh * b.scale).max(1.0) as f32],
+            size: [(sw * NOISE_CELL * b.scale).max(1.0) as f32, (sh * NOISE_CELL * b.scale).max(1.0) as f32],
             origin: [ox as f32, oy as f32],
             center: [cx as f32, cy as f32],
             perspective: pr.b("transform/perspectiveOffset"),
@@ -519,14 +524,34 @@ mod tests {
 
     #[test]
     fn noise_types_differ_and_block_is_piecewise_constant() {
-        let a = run("ec.noise.fractal", &[("noiseType", Value::Enum(0)), ("complexity", num(1.0)), ("transform/scale", num(10.0))]);
-        // Block noise: neighbours inside one 10 px cell share a value.
+        let a = run("ec.noise.fractal", &[("noiseType", Value::Enum(0)), ("complexity", num(1.0)), ("transform/scale", num(15.0))]);
+        // Block noise: neighbours inside one 10 px cell (Scale 15) share a value.
         assert_eq!(a.get(4, 4), a.get(5, 5));
         let others: Vec<Image> = (1..4).map(|t| run("ec.noise.fractal", &[("noiseType", Value::Enum(t)), ("transform/scale", num(10.0))])).collect();
         assert_ne!(others[0], others[1]);
         assert_ne!(others[1], others[2]);
     }
 
+    /// After Effects 2026 (R9): Block noise at Scale 100, Complexity 1 changes value every
+    /// 66.67 px along a row.
+    #[test]
+    fn block_noise_cells_are_two_thirds_of_scale_as_in_after_effects() {
+        let img = run_fx(
+            "ec.noise.fractal",
+            &[("noiseType", Value::Enum(0)), ("complexity", num(1.0)), ("blendingMode", Value::Enum(BLEND_NONE))],
+            Image::filled(400, 8, [0.0, 0.0, 0.0, 1.0]),
+            0.0,
+            EffectEnv::default(),
+        )
+        .img;
+        let changes: Vec<i64> = (1..400).filter(|&x| img.get(x, 4) != img.get(x - 1, 4)).collect();
+        assert!(changes.len() >= 4, "{changes:?}");
+        for w in changes.windows(2) {
+            let d = (w[1] - w[0]) as f64;
+            assert!((d - 200.0 / 3.0).abs() <= 1.0, "cell width {d}: {changes:?}");
+        }
+    }
+
     #[test]
     fn scale_width_height_apply_without_uniform_scaling() {
         let base = &[("complexity", num(1.0)), ("transform/scale", num(8.0))];

crates/gpu/src/effects.rs

@@ -529,9 +529,19 @@ fn pointwise(e: &mut Enc, id: &str, ctx: &EffectCtx, b: GBuf) -> Option<GBuf> {
             let sub = (f("subSettings/subScaling") / 100.0).clamp(0.1, 1.0);
             p.u[0] = [10, kind, octaves.ceil() as u32, f("evolutionOptions/seed") as u32 ^ 0x51ed];
             p.u[1] = [pr.b("invert") as u32, pr.e("overflow"), mode, 0];
-            p.f[0] = [f("contrast") as f32 / 100.0, f("brightness") as f32 / 100.0, (sw * b.scale).max(1.0) as f32, (octaves - octaves.floor()) as f32];
+            p.f[0] = [
+                f("contrast") as f32 / 100.0,
+                f("brightness") as f32 / 100.0,
+                (sw * effectcraft_effects::NOISE_CELL * b.scale).max(1.0) as f32,
+                (octaves - octaves.floor()) as f32,
+            ];
             p.f[1] = [ox as f32, oy as f32, sr, cr];
-            p.f[2] = [f("evolution") as f32 / 360.0, f("blend") as f32 / 100.0, (f("opacity") as f32 / 100.0).clamp(0.0, 1.0), (sh * b.scale).max(1.0) as f32];
+            p.f[2] = [
+                f("evolution") as f32 / 360.0,
+                f("blend") as f32 / 100.0,
+                (f("opacity") as f32 / 100.0).clamp(0.0, 1.0),
+                (sh * effectcraft_effects::NOISE_CELL * b.scale).max(1.0) as f32,
+            ];
             p.f[3] = [(f("subSettings/subInfluence") as f32 / 100.0).clamp(0.0, 1.0), 1.0 / sub as f32, 0.0, 0.0];
         }
         _ => return None,

docs/effects-parity.md

@@ -37,7 +37,7 @@ corpus compares renders, each effect is assumed to differ somewhere, and users k
 | Immersive Video | 12 | 12 | — |
 | 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 |
+| Noise & Grain | 13 | 12 | Fractal / Turbulent Noise lattice matches After Effects 2026 (Scale 100 = 66.7 px cells); the noise values themselves differ (seeds) and Soft Linear contrast is about 20 % lower than AE's; Curl Noise (#463); Match Grain on the CPU |
 | Obsolete | 9 | 9 | — |
 | Paint | 1 | 0 | Tablet pressure not read ([hardware-parity.md](hardware-parity.md)) |
 | Perspective | 10 | 9 | Chromatic Aberrations pan/tilt crash (#580) |
@@ -69,6 +69,7 @@ the GPU is performance, not parity.
 | 2026-10-19 | minor | Radial Blur repeats the edge instead of sampling transparency outside the layer, measured against After Effects 2026 renders (CPU and GPU) |
 | 2026-10-19 | minor | Venetian Blinds: stripes measured from the layer centre, both band edges Gaussian (σ = Feather / 2), measured against After Effects 2026 (CPU and GPU) |
 | 2026-10-19 | minor | Radial Wipe: Feather is in pixels on both edges of the wiped wedge (was degrees on the moving edge only), measured against After Effects 2026 (CPU and GPU) |
+| 2026-10-19 | minor | Fractal / Turbulent Noise: lattice cell = Scale × 2/3 px (Block noise every 66.7 px at Scale 100, as After Effects 2026), CPU and GPU |
 | 2026-10-12 | minor | Parameters 3,014 to 3,017 (effects.md); #303, #514, #526, #533–#536 marked closed instead of pending |
 | 2026-10-12 | minor | Effect colour labels (26.5) added in Effect Controls |
 | 2026-10-12 | minor | Tint's Swap Colors button and agent-drivable command (#963); undo/redo, instance targeting, animated layer-time edits and invalid-input tests |