fix: error in surface area calculation

automated_test.py

@@ -723,7 +723,13 @@ def test_contacts_surface_area():
   assert res[(1,3)] == 1
   assert res[(1,4)] == 1
   assert res[(1,5)] == 1
-
+
+  data = np.ones((3,3,3))
+  data[1,1,1] = 2
+  labels_out = cc3d.connected_components(data, connectivity=6)
+  res = cc3d.contacts(labels_out, connectivity=6, surface_area=True)
+  assert res[(1,2)] == 6
+
 def test_contacts_26():
   labels = np.zeros( (10, 10, 10), dtype=np.uint32 )
 

cc3d_graphs.hpp

@@ -317,7 +317,6 @@ extract_region_graph(
 
 	T cur = 0;
 	T label = 0;
-	T last_label = 0;
 
 	std::unordered_map<std::pair<T,T>, float, pair_hash> edges;
 
@@ -332,25 +331,19 @@ extract_region_graph(
 				}
 
 				compute_neighborhood(neighborhood, x, y, z, sx, sy, sz, connectivity);
-
-				last_label = cur;
 
 				for (int i = 0; i < connectivity / 2; i++) {
 					int64_t neighboridx = loc + neighborhood[i];
 					label = labels[neighboridx];
 
-					if (label == 0 || label == last_label) {
+					if (label == 0) {
 						continue;
 					}
-					else if (label != cur) {
-						if (cur > label) {
-							edges[std::pair<T,T>(label, cur)] += areas[i];
-						}
-						else {
-							edges[std::pair<T,T>(cur, label)] += areas[i];
-						}
-
-						last_label = label;
+					else if (cur > label) {
+						edges[std::pair<T,T>(label, cur)] += areas[i];
+					}
+					else if (cur < label) {
+						edges[std::pair<T,T>(cur, label)] += areas[i];
 					}
 				}
 			}