diff --git a/ui/dr-ui/src/develop.rs b/ui/dr-ui/src/develop.rs
index 9583996..be8373d 100644
--- a/ui/dr-ui/src/develop.rs
+++ b/ui/dr-ui/src/develop.rs
@@ -1105,6 +1105,86 @@ impl DevelopSession {
         }
     }
 
+    /// Edge transition half-width, in fractions of the shorter edge.
+    pub fn set_mask_feather(&mut self, id: &str, feather: f32) {
+        if let Some(layer) = self.graph.masks_mut().get_mut(id) {
+            layer.feather = feather.clamp(0.0, 1.0);
+            self.history.record(&self.graph, Edit::Op(OpId("mask-feather")));
+        }
+    }
+
+    pub fn set_mask_falloff(&mut self, id: &str, index: usize) {
+        use dr_pipeline::mask::Falloff;
+        let Some(&falloff) = Falloff::ALL.get(index) else {
+            return;
+        };
+        if let Some(layer) = self.graph.masks_mut().get_mut(id) {
+            layer.falloff = falloff;
+            self.history.record(&self.graph, Edit::Discrete);
+        }
+    }
+
+    pub fn set_mask_morphology(&mut self, id: &str, index: usize) {
+        use dr_pipeline::mask::Morphology;
+        let Some(&morphology) = Morphology::ALL.get(index) else {
+            return;
+        };
+        if let Some(layer) = self.graph.masks_mut().get_mut(id) {
+            layer.morphology = morphology;
+            // Picking an operation with no amount set would appear to do
+            // nothing, and the user would reasonably conclude it is broken.
+            if morphology != Morphology::None && layer.morph_radius <= 0.0 {
+                layer.morph_radius = 0.006;
+            }
+            self.history.record(&self.graph, Edit::Discrete);
+        }
+    }
+
+    pub fn set_mask_morph_radius(&mut self, id: &str, radius: f32) {
+        if let Some(layer) = self.graph.masks_mut().get_mut(id) {
+            layer.morph_radius = radius.clamp(0.0, 1.0);
+            self.history.record(&self.graph, Edit::Op(OpId("mask-morph")));
+        }
+    }
+
+    /// Which falloff a layer uses, as an index into `Falloff::ALL`.
+    pub fn mask_falloff(&self, id: &str) -> usize {
+        use dr_pipeline::mask::Falloff;
+        self.graph.masks().get(id).map_or(0, |l| {
+            Falloff::ALL.iter().position(|&f| f == l.falloff).unwrap_or(0)
+        })
+    }
+
+    pub fn mask_morphology(&self, id: &str) -> usize {
+        use dr_pipeline::mask::Morphology;
+        self.graph.masks().get(id).map_or(0, |l| {
+            Morphology::ALL
+                .iter()
+                .position(|&m| m == l.morphology)
+                .unwrap_or(0)
+        })
+    }
+
+    pub fn mask_feather(&self, id: &str) -> f32 {
+        self.graph.masks().get(id).map_or(0.0, |l| l.feather)
+    }
+
+    pub fn mask_morph_radius(&self, id: &str) -> f32 {
+        self.graph.masks().get(id).map_or(0.0, |l| l.morph_radius)
+    }
+
+    /// Whether the edge controls apply to this layer.
+    ///
+    /// Only sources that go through the distance field. A gradient carries its
+    /// own falloff in its geometry, so offering a second one would be two
+    /// controls fighting over the same edge.
+    pub fn mask_is_shapeable(&self, id: &str) -> bool {
+        use dr_pipeline::mask::MaskSource;
+        self.graph.masks().get(id).is_some_and(|l| {
+            matches!(l.source, MaskSource::Subject { .. } | MaskSource::Regions { .. })
+        })
+    }
+
     pub fn set_mask_opacity(&mut self, id: &str, opacity: f32) {
         if let Some(layer) = self.graph.masks_mut().get_mut(id) {
             layer.opacity = opacity.clamp(0.0, 1.0);
diff --git a/ui/dr-ui/src/masks_ui.rs b/ui/dr-ui/src/masks_ui.rs
index 8eff319..97810f6 100644
--- a/ui/dr-ui/src/masks_ui.rs
+++ b/ui/dr-ui/src/masks_ui.rs
@@ -47,6 +47,11 @@ pub(crate) fn sync(window: &AppWindow, session: &Rc<RefCell<Option<DevelopSessio
             kind: s.mask_kind(&id).into(),
             inverted: s.mask_inverted(&id),
             opacity: s.mask_opacity(&id),
+            feather: s.mask_feather(&id),
+            falloff: s.mask_falloff(&id) as i32,
+            morphology: s.mask_morphology(&id) as i32,
+            morph_radius: s.mask_morph_radius(&id),
+            shapeable: s.mask_is_shapeable(&id),
             id: id.into(),
             label: label.into(),
             enabled,
@@ -280,6 +285,64 @@ pub(crate) fn wire(
         });
     }
 
+    // --- the edge treatment -------------------------------------------------
+    //
+    // All four read one distance field, so all four are live: nothing here
+    // rebuilds anything except a compound morphology, which `develop` keys on
+    // separately.
+    {
+        let weak = window.as_weak();
+        let session = session.clone();
+        let redraw = redraw.clone();
+        window.on_mask_feather_changed(move |id, value| {
+            let Some(w) = weak.upgrade() else { return };
+            if let Some(s) = session.borrow_mut().as_mut() {
+                s.set_mask_feather(&id, value);
+            }
+            sync(&w, &session);
+            redraw(&w);
+        });
+    }
+    {
+        let weak = window.as_weak();
+        let session = session.clone();
+        let redraw = redraw.clone();
+        window.on_mask_falloff_picked(move |id, index| {
+            let Some(w) = weak.upgrade() else { return };
+            if let Some(s) = session.borrow_mut().as_mut() {
+                s.set_mask_falloff(&id, index.max(0) as usize);
+            }
+            sync(&w, &session);
+            redraw(&w);
+        });
+    }
+    {
+        let weak = window.as_weak();
+        let session = session.clone();
+        let redraw = redraw.clone();
+        window.on_mask_morphology_picked(move |id, index| {
+            let Some(w) = weak.upgrade() else { return };
+            if let Some(s) = session.borrow_mut().as_mut() {
+                s.set_mask_morphology(&id, index.max(0) as usize);
+            }
+            sync(&w, &session);
+            redraw(&w);
+        });
+    }
+    {
+        let weak = window.as_weak();
+        let session = session.clone();
+        let redraw = redraw.clone();
+        window.on_mask_morph_radius_changed(move |id, value| {
+            let Some(w) = weak.upgrade() else { return };
+            if let Some(s) = session.borrow_mut().as_mut() {
+                s.set_mask_morph_radius(&id, value);
+            }
+            sync(&w, &session);
+            redraw(&w);
+        });
+    }
+
     // --- adding layers ------------------------------------------------------
     {
         let weak = window.as_weak();
diff --git a/ui/dr-ui/ui/app.slint b/ui/dr-ui/ui/app.slint
index 7cfb336..7ec1ea4 100644
--- a/ui/dr-ui/ui/app.slint
+++ b/ui/dr-ui/ui/app.slint
@@ -836,6 +836,10 @@ export component AppWindow inherits Window {
     callback mask-toggled(string, bool);
     callback mask-invert-toggled(string, bool);
     callback mask-opacity-changed(string, float);
+    callback mask-feather-changed(string, float);
+    callback mask-falloff-picked(string, int);
+    callback mask-morphology-picked(string, int);
+    callback mask-morph-radius-changed(string, float);
     callback add-gradient-mask(bool);
     callback add-subject-mask(int);
 
@@ -1922,6 +1926,18 @@ in property <bool> panel-visible: true;
                             mask-opacity-changed(id, v) => {
                                 root.mask-opacity-changed(id, v);
                             }
+                            mask-feather-changed(id, v) => {
+                                root.mask-feather-changed(id, v);
+                            }
+                            mask-falloff-picked(id, i) => {
+                                root.mask-falloff-picked(id, i);
+                            }
+                            mask-morphology-picked(id, i) => {
+                                root.mask-morphology-picked(id, i);
+                            }
+                            mask-morph-radius-changed(id, v) => {
+                                root.mask-morph-radius-changed(id, v);
+                            }
                             add-gradient(radial) => { root.add-gradient-mask(radial); }
                             add-subject(i) => { root.add-subject-mask(i); }
                         }
diff --git a/ui/dr-ui/ui/masks.slint b/ui/dr-ui/ui/masks.slint
index 408ad0e..fed949c 100644
--- a/ui/dr-ui/ui/masks.slint
+++ b/ui/dr-ui/ui/masks.slint
@@ -8,7 +8,7 @@
 
 import { Theme } from "theme.slint";
 import { Button, Caption, IconButton, Label, PanelHeading, Value } from "widgets.slint";
-import { SliderRow } from "controls.slint";
+import { Segmented, SliderRow } from "controls.slint";
 
 /// One layer in the stack.
 export struct MaskRow {
@@ -22,6 +22,17 @@ export struct MaskRow {
     selected: bool,
     inverted: bool,
     opacity: float,
+    /// Edge transition half-width, as a fraction of the frame's shorter edge.
+    feather: float,
+    /// Index into `Falloff::ALL`.
+    falloff: int,
+    /// Index into `Morphology::ALL`.
+    morphology: int,
+    morph-radius: float,
+    /// Whether the edge controls apply. A gradient has its own geometry and
+    /// does not go through the distance field, so showing them would offer
+    /// controls that do nothing.
+    shapeable: bool,
     /// Its region ids came from a different segmentation than the one loaded,
     /// so applying it would produce a confidently wrong shape.
     stale: bool,
@@ -49,6 +60,10 @@ component MaskEntry inherits Rectangle {
     callback toggled(bool);
     callback invert-toggled(bool);
     callback opacity-changed(float);
+    callback feather-changed(float);
+    callback falloff-picked(int);
+    callback morphology-picked(int);
+    callback morph-radius-changed(float);
 
     height: layout.preferred-height;
     background: root.data.selected ? Theme.surface-raised : transparent;
@@ -155,6 +170,46 @@ component MaskEntry inherits Rectangle {
                     emphasised: invert.has-hover || root.data.inverted;
                 }
             }
+
+            // The edge. All of it reads one signed distance field, so these
+            // are free to move — none of them recomputes anything except a
+            // compound morphology.
+            if root.data.shapeable: SliderRow {
+                label: "Feather";
+                hint: "How far the edit fades across the edge.";
+                value: root.data.feather * 1000;
+                default-value: 4;
+                minimum: 0;
+                maximum: 60;
+                changed(v) => { root.feather-changed(v / 1000); }
+                reset => { root.feather-changed(0.004); }
+            }
+
+            if root.data.shapeable: Segmented {
+                label: "Falloff";
+                options: ["Hard", "Linear", "Smooth", "Gaussian", "Expo"];
+                selected: root.data.falloff;
+                picked(i) => { root.falloff-picked(i); }
+            }
+
+            if root.data.shapeable: Segmented {
+                label: "Edge";
+                hint: "Grow or shrink the outline the model drew. Close fills "
+                      + "pinholes; open removes specks.";
+                options: ["None", "Grow", "Shrink", "Close", "Open"];
+                selected: root.data.morphology;
+                picked(i) => { root.morphology-picked(i); }
+            }
+
+            if root.data.shapeable && root.data.morphology != 0: SliderRow {
+                label: "Amount";
+                value: root.data.morph-radius * 1000;
+                default-value: 0;
+                minimum: 0;
+                maximum: 40;
+                changed(v) => { root.morph-radius-changed(v / 1000); }
+                reset => { root.morph-radius-changed(0); }
+            }
         }
     }
 }
@@ -199,6 +254,10 @@ export component MaskPanel inherits Rectangle {
     callback mask-toggled(string, bool);
     callback mask-invert-toggled(string, bool);
     callback mask-opacity-changed(string, float);
+    callback mask-feather-changed(string, float);
+    callback mask-falloff-picked(string, int);
+    callback mask-morphology-picked(string, int);
+    callback mask-morph-radius-changed(string, float);
 
     callback add-gradient(bool);
     callback add-subject(int);
@@ -373,6 +432,10 @@ export component MaskPanel inherits Rectangle {
             toggled(on) => { root.mask-toggled(mask.id, on); }
             invert-toggled(on) => { root.mask-invert-toggled(mask.id, on); }
             opacity-changed(v) => { root.mask-opacity-changed(mask.id, v); }
+            feather-changed(v) => { root.mask-feather-changed(mask.id, v); }
+            falloff-picked(i) => { root.mask-falloff-picked(mask.id, i); }
+            morphology-picked(i) => { root.mask-morphology-picked(mask.id, i); }
+            morph-radius-changed(v) => { root.mask-morph-radius-changed(mask.id, v); }
         }
 
         // The one thing this panel has to say about the adjust panel below it,