diff --git a/crates/gpu/src/fx_noise.rs b/crates/gpu/src/fx_noise.rs
index 1a20aa453..e3bec6fcd 100644
--- a/crates/gpu/src/fx_noise.rs
+++ b/crates/gpu/src/fx_noise.rs
@@ -166,7 +166,7 @@ pub(crate) fn median_image(e: &mut Enc, img: &GpuImage, r: usize, straight: bool
     // sliding along the rest.
     let seg = (4 * r as u32).clamp(32, 512).min(q.width);
     let out = e.scratch(q.width, q.height);
-    e.dispatch("fxn_median_huang", &with_u0([r as u32, seg, 0, 0]), &q, None, &out, Some(&levels), (q.height.div_ceil(64), q.width.div_ceil(seg)));
+    e.dispatch("fxn_median_huang", &with_u0([r as u32, seg, 0, 0]), &q, None, &out, Some(&levels), (q.height, q.width.div_ceil(seg)));
     out
 }
 
diff --git a/crates/gpu/src/shaders/fx_noise.wgsl b/crates/gpu/src/shaders/fx_noise.wgsl
index 5e68e10c1..24b0d1e0b 100644
--- a/crates/gpu/src/shaders/fx_noise.wgsl
+++ b/crates/gpu/src/shaders/fx_noise.wgsl
@@ -86,9 +86,13 @@ fn fxn_median(@builtin(global_invocation_id) gid: vec3<u32>) {
 // channel (Huang). One invocation per row segment of u[0].y pixels: it fills the histogram for
 // the segment's first window, then slides right one column at a time (remove the column
 // leaving, add the one entering) and moves each channel's median by the counts below it.
-// u[0] = (r, segment length); dispatched over (rows, segments) with 64 × 1 workgroups.
+// One invocation owns the workgroup's 8 KiB histogram. Keeping the indirectly indexed
+// bins in workgroup memory avoids a large per-invocation private array. WGSL initializes
+// this memory to zero before each workgroup; no invocation shares its bins with another.
+var<workgroup> median_hist: array<u32, 2048>;
+// u[0] = (r, segment length); dispatched over (rows, segments) with 1 × 1 workgroups.
 // data = the 512 CPU-rounded level / 511 values.
-@compute @workgroup_size(64, 1)
+@compute @workgroup_size(1, 1)
 fn fxn_median_huang(@builtin(global_invocation_id) gid: vec3<u32>) {
     let dims = out_dims();
     let y = i32(gid.x);
@@ -100,14 +104,13 @@ fn fxn_median_huang(@builtin(global_invocation_id) gid: vec3<u32>) {
     let x1 = min(x0 + seg, dims.x);
     let r = i32(P.u[0].x);
     let half = u32((2 * r + 1) * (2 * r + 1) / 2);
-    var hist: array<u32, 2048>;
     for (var dy = -r; dy <= r; dy++) {
         for (var dx = -r; dx <= r; dx++) {
             let v = vec4<u32>(tex_get_clamped(src, x0 + dx, y + dy));
-            hist[v.x] += 1u;
-            hist[512u + v.y] += 1u;
-            hist[1024u + v.z] += 1u;
-            hist[1536u + v.w] += 1u;
+            median_hist[v.x] += 1u;
+            median_hist[512u + v.y] += 1u;
+            median_hist[1024u + v.z] += 1u;
+            median_hist[1536u + v.w] += 1u;
         }
     }
     // Per channel: the median level and the count of values below it.
@@ -119,11 +122,11 @@ fn fxn_median_huang(@builtin(global_invocation_id) gid: vec3<u32>) {
                 let o = vec4<u32>(tex_get_clamped(src, x - 1 - r, y + dy));
                 let n = vec4<u32>(tex_get_clamped(src, x + r, y + dy));
                 for (var c = 0u; c < 4u; c++) {
-                    hist[c * 512u + o[c]] -= 1u;
+                    median_hist[c * 512u + o[c]] -= 1u;
                     if (o[c] < med[c]) {
                         lt[c] -= 1u;
                     }
-                    hist[c * 512u + n[c]] += 1u;
+                    median_hist[c * 512u + n[c]] += 1u;
                     if (n[c] < med[c]) {
                         lt[c] += 1u;
                     }
@@ -134,10 +137,10 @@ fn fxn_median_huang(@builtin(global_invocation_id) gid: vec3<u32>) {
             let base = c * 512u;
             while (lt[c] > half) {
                 med[c] -= 1u;
-                lt[c] -= hist[base + med[c]];
+                lt[c] -= median_hist[base + med[c]];
             }
-            while (lt[c] + hist[base + med[c]] <= half) {
-                lt[c] += hist[base + med[c]];
+            while (lt[c] + median_hist[base + med[c]] <= half) {
+                lt[c] += median_hist[base + med[c]];
                 med[c] += 1u;
             }
         }