Correct expectation for test_offset_not_none

See bug report here: scikit-image/scikit-image#7315

benchmarking/h_maxima/test_reconstruction.py

@@ -8,8 +8,10 @@
 from numpy.testing import assert_array_almost_equal
 
 from skimage._shared.utils import _supported_float_type
+import skimage.morphology.grayreconstruct
 
 # from skimage.morphology.grayreconstruct import reconstruction
+from benchmark_utils import opencv_reconstruct
 from fast_reconstruct_wrapper import cython_reconstruct_wrapper as reconstruction
 
 xfail = pytest.mark.xfail
@@ -241,7 +243,7 @@ def test_offset_not_none():
     """Test reconstruction with valid offset parameter"""
     seed = np.array([[0, 3, 6, 2, 1, 1, 1, 4, 2, 0]])
     mask = np.array([[0, 8, 6, 8, 8, 8, 8, 4, 4, 0]])
-    expected = np.array([[0, 3, 6, 6, 6, 6, 6, 4, 4, 0]])
+    expected = np.array([[0, 6, 6, 4, 4, 4, 4, 4, 2, 0]])
 
     assert_array_almost_equal(
         reconstruction(
@@ -253,3 +255,32 @@ def test_offset_not_none():
         ),
         expected,
     )
+
+
+@xfail(reason="scikit bug? https://github.com/scikit-image/scikit-image/issues/7315")
+def test_offset_not_none_vs_opencv():
+    """Test reconstruction with valid offset parameter"""
+    seed = np.array([0, 3, 6, 2, 1, 1, 1, 4, 2, 0])
+    mask = np.array([0, 8, 6, 8, 8, 8, 8, 4, 4, 0])
+    expected = np.array([0, 6, 6, 4, 4, 4, 4, 4, 2, 0])
+
+    footprint = np.array([1, 1, 1])
+
+    opencv_result = opencv_reconstruct(
+        seed.astype(np.uint8, copy=True),
+        mask.astype(np.uint8, copy=True),
+        footprint,
+        (0, 0),
+    )
+    assert_array_almost_equal(opencv_result, expected)
+
+    # This actually fails, it wants a different kind of offset
+    # but [[0], [0]] doesn't work nor does [0, 0] nor [[0, 0]]
+    scikit_result = skimage.morphology.grayreconstruct.reconstruction(
+        seed,
+        mask,
+        method="dilation",
+        footprint=np.array([[1, 1, 1]], dtype=np.uint8),
+        offset=np.array([[0], [0]], dtype=np.uint8),
+    )
+    assert_array_almost_equal(scikit_result, expected)