diff --git a/ui/dr-ui/src/merge.rs b/ui/dr-ui/src/merge.rs
index 8babb40..1f9fe0c 100644
--- a/ui/dr-ui/src/merge.rs
+++ b/ui/dr-ui/src/merge.rs
@@ -603,6 +603,41 @@ fn preview(
             out[o + 3] = 255;
         }
     }
+
+    // Each frame's outline, so the page shows *frames* and not one picture:
+    // a sweep of frames overlapping by more than half reads as a single
+    // photograph otherwise, which is what a photographer looking for a
+    // misplaced frame needs to see through. Walked along each border and
+    // drawn where it lands, two pixels wide, in a colour the scene does not
+    // have.
+    let steps = 600;
+    for k in 0..proxies.len() {
+        for s in 0..steps {
+            let t = s as f64 / steps as f64;
+            for p in [
+                (-fw / 2.0 + fw * t, -fh / 2.0),
+                (-fw / 2.0 + fw * t, fh / 2.0 - 1.0),
+                (-fw / 2.0, -fh / 2.0 + fh * t),
+                (fw / 2.0 - 1.0, -fh / 2.0 + fh * t),
+            ] {
+                let d = cameras.bearing(k, p);
+                let Some((u, v)) = projection.from_direction(scale, d) else { continue };
+                let x = ((u - bounds.min_u) / px) as i64;
+                let y = ((v - bounds.min_v) / px) as i64;
+                for (dx, dy) in [(0, 0), (1, 0), (0, 1), (1, 1)] {
+                    let (xx, yy) = (x + dx, y + dy);
+                    if xx < 0 || yy < 0 || xx >= out_w as i64 || yy >= out_h as i64 {
+                        continue;
+                    }
+                    let o = (yy as usize * out_w + xx as usize) * 4;
+                    out[o] = 255;
+                    out[o + 1] = 176;
+                    out[o + 2] = 0;
+                    out[o + 3] = 255;
+                }
+            }
+        }
+    }
     (out_w as u32, out_h as u32, out)
 }
 
diff --git a/ui/dr-ui/ui/merge.slint b/ui/dr-ui/ui/merge.slint
index ecbcec0..158d54e 100644
--- a/ui/dr-ui/ui/merge.slint
+++ b/ui/dr-ui/ui/merge.slint
@@ -139,8 +139,13 @@ export component MergePage inherits Rectangle {
                     // was found at: ghosting here is the alignment's error,
                     // and what it looks like is what the photographer is
                     // confirming.
+                    // As tall as the picture needs up to most of the page,
+                    // and as wide as it is at that height: a four-frame
+                    // perspective merge is nearly square, a twelve-frame
+                    // cylinder is a strip, and either should fill what it
+                    // can rather than sit in a letterbox.
                     if root.preview.width > 0: Rectangle {
-                        height: min(320px, parent.width * root.preview.height / max(1, root.preview.width));
+                        height: min(root.height * 0.55, parent.width * root.preview.height / max(1, root.preview.width));
                         background: Theme.rule;
                         Image {
                             source: root.preview;
@@ -151,6 +156,10 @@ export component MergePage inherits Rectangle {
                     }
 
                     Caption { text: root.summary; wrap: word-wrap; }
+                    Caption {
+                        text: "Each frame is outlined in amber where it lands. Ghosting in an overlap is the alignment's error.";
+                        wrap: word-wrap;
+                    }
 
                     Segmented {
                         label: "Projection";