diff --git a/viewer/image_viewer/JFJochSimpleImage.cpp b/viewer/image_viewer/JFJochSimpleImage.cpp
index 75b43270..5e561cfa 100644
--- a/viewer/image_viewer/JFJochSimpleImage.cpp
+++ b/viewer/image_viewer/JFJochSimpleImage.cpp
@@ -16,8 +16,9 @@ JFJochSimpleImage::JFJochSimpleImage(QWidget *parent)
     auto *scn = new QGraphicsScene(this);
     setScene(scn);
 
-    // Keep overlays in pixel units independent of zoom (for labels font sizing)
-    setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
+    // Repaint only what changed. FullViewportUpdate redraws the entire viewport on any change,
+    // which is wasted work locally and, on a remote session, uploads far more than was touched.
+    setViewportUpdateMode(QGraphicsView::SmartViewportUpdate);
 
     // The predicted/float image is unreadable with 3-decimal per-pixel labels.
     label_decimals_ = 1;