diff --git a/crates/ui-egui/src/frames.rs b/crates/ui-egui/src/frames.rs
index c79b023b2..9671e72a2 100644
--- a/crates/ui-egui/src/frames.rs
+++ b/crates/ui-egui/src/frames.rs
@@ -438,14 +438,22 @@ pub trait RemoteFrames: Send + Sync {
 
 /// Whether a comp (or a comp it nests) has a layer with enabled effects.
 pub fn comp_has_effects(project: &Project, comp: ItemId) -> bool {
-    fn walk(p: &Project, comp: ItemId, depth: usize) -> bool {
+    // Each comp is answered once: a comp nested by many layers at each of several levels was
+    // walked again for every path to it.
+    fn walk(p: &Project, comp: ItemId, depth: usize, seen: &mut std::collections::HashMap<ItemId, bool>) -> bool {
+        if let Some(&r) = seen.get(&comp) {
+            return r;
+        }
+        seen.insert(comp, false);
         let Some(c) = p.comp(comp) else { return false };
-        c.layers.iter().any(|l| {
+        let r = c.layers.iter().any(|l| {
             l.switches.effects && l.effects().is_some_and(|fx| fx.groups().any(|g| g.enabled))
-                || depth < 16 && matches!(l.source, effectcraft_engine::project::LayerSource::Comp { item } if walk(p, item, depth + 1))
-        })
+                || depth < 16 && matches!(l.source, effectcraft_engine::project::LayerSource::Comp { item } if walk(p, item, depth + 1, seen))
+        });
+        seen.insert(comp, r);
+        r
     }
-    walk(project, comp, 0)
+    walk(project, comp, 0, &mut std::collections::HashMap::new())
 }
 
 pub struct Frames {
diff --git a/crates/ui-egui/src/frames/tests.rs b/crates/ui-egui/src/frames/tests.rs
index d04793f50..a8564d8c6 100644
--- a/crates/ui-egui/src/frames/tests.rs
+++ b/crates/ui-egui/src/frames/tests.rs
@@ -1084,3 +1084,23 @@ fn timing_markers_and_expressions_still_change_the_frames() {
     s.execute("layer.addMarker", json!({"comp": outer.0, "layers": [solid], "time": 0.75})).unwrap();
     assert_ne!(at(&s), o2, "an expression can read the marker, so the frames change");
 }
+
+#[test]
+fn effect_detection_answers_each_comp_once() {
+    // Sixteen levels, each comp holding eight layers of the one below and no effects: 8^16 walks
+    // without a memo. Answered at once.
+    use effectcraft_engine::project::{Comp, ItemKind, LayerSource, build};
+    use effectcraft_engine::time::{FrameRate, Tick};
+    let mut p = Project::default();
+    let base = Comp::new(8, 8, FrameRate::new(25, 1), Tick::from_seconds_f64(1.0));
+    let mut below = p.add_item("C", effectcraft_engine::color::Label::Sandstone, None, ItemKind::Comp(base.clone().into()));
+    for _ in 0..16 {
+        let layers: Vec<_> = (0..8).map(|_| build::layer(&mut p, &base, "a", LayerSource::Comp { item: below }, (0, 0), None)).collect();
+        let mut c = base.clone();
+        c.layers = layers.into();
+        below = p.add_item("C", effectcraft_engine::color::Label::Sandstone, None, ItemKind::Comp(c.into()));
+    }
+    let start = std::time::Instant::now();
+    assert!(!comp_has_effects(&p, below));
+    assert!(start.elapsed() < std::time::Duration::from_secs(5));
+}
diff --git a/crates/ui-egui/src/panels/scriptui_view.rs b/crates/ui-egui/src/panels/scriptui_view.rs
index 753b2884e..038ed5e15 100644
--- a/crates/ui-egui/src/panels/scriptui_view.rs
+++ b/crates/ui-egui/src/panels/scriptui_view.rs
@@ -329,7 +329,7 @@ fn image_texture(ctx: &egui::Context, img: &ImageRef, services: &dyn Services) -
     if let Some(cached) = ctx.data(|d| d.get_temp::<Option<egui::TextureHandle>>(id)) {
         return cached;
     }
-    let tex = img.bytes(services).and_then(|b| image::load_from_memory(&b).ok()).map(|d| {
+    let tex = img.bytes(services).and_then(|b| decode_ui_image(&b)).map(|d| {
         let rgba = d.to_rgba8();
         let ci = egui::ColorImage::from_rgba_unmultiplied([rgba.width() as usize, rgba.height() as usize], rgba.as_raw());
         ctx.load_texture(format!("scriptui-image-{}", img.name), ci, egui::TextureOptions::LINEAR)
@@ -338,6 +338,21 @@ fn image_texture(ctx: &egui::Context, img: &ImageRef, services: &dyn Services) -
     tex
 }
 
+/// The largest side of a ScriptUI image (icons and banners are far smaller).
+const MAX_UI_IMAGE_SIDE: u32 = 4096;
+
+/// A ScriptUI image decoded within [`MAX_UI_IMAGE_SIDE`] per side and a matching allocation
+/// limit, checked from the header before the pixels (and their RGBA copy) are allocated.
+fn decode_ui_image(bytes: &[u8]) -> Option<image::DynamicImage> {
+    let mut r = image::ImageReader::new(std::io::Cursor::new(bytes)).with_guessed_format().ok()?;
+    let mut limits = image::Limits::default();
+    limits.max_image_width = Some(MAX_UI_IMAGE_SIDE);
+    limits.max_image_height = Some(MAX_UI_IMAGE_SIDE);
+    limits.max_alloc = Some(u64::from(MAX_UI_IMAGE_SIDE) * u64::from(MAX_UI_IMAGE_SIDE) * 16);
+    r.limits(limits);
+    r.decode().ok()
+}
+
 /// An image control's or icon button's image, fitted (aspect kept) and centred in `r`.
 fn paint_image(ui: &egui::Ui, r: Rect, img: &ImageRef, services: &dyn Services) -> bool {
     let Some(tex) = image_texture(ui.ctx(), img, services) else { return false };