diff --git a/notebooks/ade20k_starter.ipynb b/notebooks/ade20k_starter.ipynb
index 6008c26..6d71957 100644
--- a/notebooks/ade20k_starter.ipynb
+++ b/notebooks/ade20k_starter.ipynb
@@ -86,7 +86,9 @@
   {
    "cell_type": "code",
    "execution_count": 6,
-   "metadata": {},
+   "metadata": {
+    "scrolled": true
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -189,6 +191,8 @@
     "img = cv2.imread(info['img_name'])[:,:,::-1]\n",
     "seg = cv2.imread(info['segm_name'])[:,:,::-1]\n",
     "seg_mask = seg.copy()\n",
+    "\n",
+    "# The 0 index in seg_mask corresponds to background (not annotated) pixels\n",
     "seg_mask[info['class_mask'] != obj_id+1] *= 0\n",
     "plt.figure(figsize=(15,5))\n",
     "\n",