diff --git a/viewer/image_viewer/JFJochImage.cpp b/viewer/image_viewer/JFJochImage.cpp
index 62ef5b1c..f1452e44 100644
--- a/viewer/image_viewer/JFJochImage.cpp
+++ b/viewer/image_viewer/JFJochImage.cpp
@@ -67,10 +67,20 @@ void JFJochImage::onScroll(int value) {
     updateOverlay();
 }
 
+void JFJochImage::ScheduleRenderImage() {
+    if (render_pending_)
+        return;
+    render_pending_ = true;
+    QTimer::singleShot(0, this, [this] {
+        render_pending_ = false;
+        RenderImage();
+        Redraw();
+    });
+}
+
 void JFJochImage::changeBackground(float val) {
     background = val;
-    RenderImage();
-    Redraw();
+    ScheduleRenderImage();
 }
 
 void JFJochImage::changeForeground(float val) {
@@ -78,8 +88,7 @@ void JFJochImage::changeForeground(float val) {
     emit autoForegroundChanged(false);
     foreground = val;
     // Regenerate the image
-    RenderImage();
-    Redraw();
+    ScheduleRenderImage();
 }
 
 void JFJochImage::setColorMap(int color_map) {
diff --git a/viewer/image_viewer/JFJochImage.h b/viewer/image_viewer/JFJochImage.h
index a6f9e3f2..623f8125 100644
--- a/viewer/image_viewer/JFJochImage.h
+++ b/viewer/image_viewer/JFJochImage.h
@@ -119,6 +119,11 @@ protected:
 
     void updateOverlay();
     void RenderImage();
+    // Re-render once the event queue drains. The foreground slider and the wheel emit far
+    // faster than a large image can be recoloured, so intermediate values are dropped
+    // instead of queueing a full recolour per event.
+    void ScheduleRenderImage();
+    bool render_pending_ = false;
     void Redraw();
     void CalcROI();