diff --git a/elf/tracking/tracking_utils.py b/elf/tracking/tracking_utils.py
index 4a4c74d..c1ed15b 100644
--- a/elf/tracking/tracking_utils.py
+++ b/elf/tracking/tracking_utils.py
@@ -8,7 +8,8 @@
 import numpy as np
 
 from scipy.spatial.distance import cdist
-from skimage.measure import regionprops
+from skimage.measure import regionprops, label
+from scipy.ndimage import binary_closing
 from skimage.segmentation import relabel_sequential
 from tqdm import trange
 
@@ -23,7 +24,7 @@ def compute_overlap_between_frames(frame_a, frame_b):
         source_ids = [src for node_id, ovlp in zip(node_ids, overlaps) for src in [node_id] * len(ovlp[0])]
         target_ids = [ov for ovlp in overlaps for ov in ovlp[0]]
         overlap_values = [ov for ovlp in overlaps for ov in ovlp[1]]
-        assert len(source_ids) == len(target_ids) == len(overlap_values),\
+        assert len(source_ids) == len(target_ids) == len(overlap_values), \
             f"{len(source_ids)}, {len(target_ids)}, {len(overlap_values)}"
 
         edges = [
@@ -50,9 +51,9 @@ def compute_edges_from_centroid_distance(segmentation, max_distance, normalize_d
     centroids_and_labels = [[prop.centroid[0], prop.centroid[1:], prop.label] for prop in props]
 
     centroids, labels = {}, {}
-    for t, centroid, label in centroids_and_labels:
+    for t, centroid, label_id in centroids_and_labels:
         centroids[t] = centroids.get(t, []) + [centroid]
-        labels[t] = labels.get(t, []) + [label]
+        labels[t] = labels.get(t, []) + [label_id]
     centroids = {t: np.stack(np.array(val)) for t, val in centroids.items()}
     labels = {t: np.array(val) for t, val in labels.items()}
 
@@ -106,3 +107,63 @@ def relabel_segmentation_across_time(segmentation):
         offset = frame.max()
         relabeled.append(frame)
     return np.stack(relabeled)
+
+
+def preprocess_closing(slice_segmentation, gap_closing, verbose=True):
+    binarized = slice_segmentation > 0
+    structuring_element = np.zeros((3, 1, 1))
+    structuring_element[:, 0, 0] = 1
+    closed_segmentation = binary_closing(binarized, iterations=gap_closing, structure=structuring_element)
+
+    new_segmentation = np.zeros_like(slice_segmentation)
+    n_slices = new_segmentation.shape[0]
+
+    def process_slice(z, offset):
+        seg_z = slice_segmentation[z]
+
+        # Closing does not work for the first and last gap slices
+        if z < gap_closing or z >= (n_slices - gap_closing):
+            seg_z, _, _ = relabel_sequential(seg_z, offset=offset)
+            offset = int(seg_z.max()) + 1
+            return seg_z, offset
+
+        # Apply connected components to the closed segmentation.
+        closed_z = label(closed_segmentation[z])
+
+        # Map objects in the closed and initial segmentation.
+        # We take objects from the closed segmentation unless they
+        # have overlap with more than one object from the initial segmentation.
+        # This indicates wrong merging of closeby objects that we want to prevent.
+        matches = ngt.overlap(closed_z, seg_z)
+        matches = {seg_id: matches.overlapArrays(seg_id, sorted=False)[0]
+                   for seg_id in range(1, int(closed_z.max() + 1))}
+        matches = {k: v[v != 0] for k, v in matches.items()}
+
+        ids_initial, ids_closed = [], []
+        for seg_id, matched in matches.items():
+            if len(matched) > 1:
+                ids_initial.extend(matched.tolist())
+            else:
+                ids_closed.append(seg_id)
+
+        seg_new = np.zeros_like(seg_z)
+        closed_mask = np.isin(closed_z, ids_closed)
+        seg_new[closed_mask] = closed_z[closed_mask]
+
+        if ids_initial:
+            initial_mask = np.isin(seg_z, ids_initial)
+            seg_new[initial_mask] = relabel_sequential(seg_z[initial_mask], offset=seg_new.max() + 1)[0]
+
+        seg_new, _, _ = relabel_sequential(seg_new, offset=offset)
+        max_z = seg_new.max()
+        if max_z > 0:
+            offset = int(max_z) + 1
+
+        return seg_new, offset
+
+    # Further optimization: parallelize
+    offset = 1
+    for z in trange(n_slices, disable=not verbose):
+        new_segmentation[z], offset = process_slice(z, offset)
+
+    return new_segmentation