From 6bface70c5ebe39ed8d30a483c06c49a2ebc150b Mon Sep 17 00:00:00 2001
From: David Manthey <david.manthey@kitware.com>
Date: Fri, 6 Dec 2024 16:12:59 -0500
Subject: [PATCH] Harden the trace boundary code (#1150)

A one pixel object could get stuck in an infinite loop in the moore
boundary call.
---
 .../label/_trace_object_boundaries_cython.pyx | 21 ++++++++++---------
 tests/test_segmentation_label.py              | 12 ++++++++++-
 2 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/histomicstk/segmentation/label/_trace_object_boundaries_cython.pyx b/histomicstk/segmentation/label/_trace_object_boundaries_cython.pyx
index 236a599fe..a71db5a72 100644
--- a/histomicstk/segmentation/label/_trace_object_boundaries_cython.pyx
+++ b/histomicstk/segmentation/label/_trace_object_boundaries_cython.pyx
@@ -26,8 +26,8 @@ def _trace_object_boundaries_cython(long[:, :] im_label not None, long connectiv
         # find starting x and y points if not defined
         if (x_start == -1) & (y_start == -1):
 
-          for i in range(nrows):
-            for j in range(ncols):
+          for i in range(1, nrows - 1):
+            for j in range(1, ncols - 1):
 
               if (im_label[i, j] > 0) & (flag == 0):
                 # check if the number of points is one
@@ -41,16 +41,17 @@ def _trace_object_boundaries_cython(long[:, :] im_label not None, long connectiv
 
     bx = []
     by = []
+    if x_start >= 0 and y_start >= 0:
 
-    if connectivity == 4:
-        bx, by = _isbf(
-            im_label, im_label_90, im_label_180, im_label_270,
-            x_start, y_start, max_length);
+        if connectivity == 4:
+            bx, by = _isbf(
+                im_label, im_label_90, im_label_180, im_label_270,
+                x_start, y_start, max_length);
 
-    else:
-        bx, by = _moore(
-            im_label, im_label_90, im_label_180, im_label_270,
-            x_start, y_start, max_length);
+        else:
+            bx, by = _moore(
+                im_label, im_label_90, im_label_180, im_label_270,
+                x_start, y_start, max_length);
 
     return np.asarray(bx), np.asarray(by)
 
diff --git a/tests/test_segmentation_label.py b/tests/test_segmentation_label.py
index 560d39c33..4803541c0 100644
--- a/tests/test_segmentation_label.py
+++ b/tests/test_segmentation_label.py
@@ -22,7 +22,7 @@ def test_trace_boundary(self):
                                [0, 0, 0, 0, 0, 0, 0, 1, 1, 0],
                                [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]], dtype=bool)
 
-        # refenece neighbors for isbf
+        # reference neighbors for isbf
         rx_isbf = [1, 1, 2, 2, 3, 4, 5, 6, 7, 8, 8, 9, 9, 8, 7, 7, 7,
                    7, 6, 6, 5, 5, 5, 4, 4, 3, 3, 3, 3, 2, 1]
         ry_isbf = [7, 8, 8, 7, 6, 6, 6, 6, 6, 7, 8, 8, 7, 7, 6, 5, 4,
@@ -46,6 +46,16 @@ def test_trace_boundary(self):
         np.testing.assert_allclose(rx_moore, x_moore[0])
         np.testing.assert_allclose(ry_moore, y_moore[0])
 
+    def test_trace_boundary_bad(self):
+        # Make sure the algorithms terminate work in a degenerate case
+        m_neighbor = np.array([[0, 0, 0, 0, 0],
+                               [0, 1, 0, 1, 0],
+                               [0, 0, 0, 0, 0]], dtype=bool)
+        x, y = trace_object_boundaries(m_neighbor, simplify_colinear_spurs=False)
+        assert not len(x)
+        x, y = trace_object_boundaries(m_neighbor, 8, simplify_colinear_spurs=False)
+        assert not len(x)
+
 
 class TestDeleteBorderLabel: