diff --git a/labelme/utils.py b/labelme/utils.py
index 7bf9e87b9..614185b2a 100644
--- a/labelme/utils.py
+++ b/labelme/utils.py
@@ -119,14 +119,31 @@ def draw_label(label, img, label_names, colormap=None):
 
 
 def shapes_to_label(img_shape, shapes, label_name_to_value, type='class'):
-    lbl = np.zeros(img_shape[:2], dtype=np.int32)
+    assert type in ['class', 'instance']
+
+    cls = np.zeros(img_shape[:2], dtype=np.int32)
+    if type == 'instance':
+        ins = np.zeros(img_shape[:2], dtype=np.int32)
+        instance_names = ['__background__']
     for shape in shapes:
         polygons = shape['points']
-        label_name = shape['label']
-        label_value = label_name_to_value[label_name]
+        label = shape['label']
+        if type == 'class':
+            cls_name = label
+        elif type == 'instance':
+            cls_name = label.split('-')[0]
+            if label not in instance_names:
+                instance_names.append(label)
+            ins_id = len(instance_names) - 1
+        cls_id = label_name_to_value[cls_name]
         mask = polygons_to_mask(img_shape[:2], polygons)
-        lbl[mask] = label_value
-    return lbl
+        cls[mask] = cls_id
+        if type == 'instance':
+            ins[mask] = ins_id
+
+    if type == 'instance':
+        return cls, ins
+    return cls
 
 
 def labelme_shapes_to_label(img_shape, shapes):