feat: refine boundary mapping to improve alignment of inner and outer source coordinates

src/anyimage/operators/cutout_tool/boundary_padding.py

@@ -51,6 +51,7 @@ def build_boundary_mapping(content_values, threshold, padding, target_shape=None
     )
     distance = padding * scale
     signed = ndimage.distance_transform_edt(mask) - ndimage.distance_transform_edt(~mask)
+    signed = np.where(signed != 0.0, signed - 0.5 * np.sign(signed), 0.0)
     inward_y = ndimage.sobel(signed, axis=0, mode="nearest")
     inward_x = ndimage.sobel(signed, axis=1, mode="nearest")
     length = np.hypot(inward_y, inward_x)

tests/anyimage/operators/test_cutout_boundary_padding.py

@@ -36,6 +36,19 @@ def test_mapping_moves_along_one_direction_instead_of_nearest_content():
     assert abs(result[1, 8, 0] - 8) < 0.5
 
 
+def test_boundary_mapping_aligns_inner_and_outer_source_coordinates():
+    values = np.zeros((9, 9), dtype=np.float32)
+    values[3:6, 3:6] = 1.0
+
+    mapping = build_boundary_mapping(values, 0.9, 2)
+
+    np.testing.assert_allclose(
+        mapping.source_x[4, 2],
+        mapping.source_x[4, 3],
+        atol=0.25,
+    )
+
+
 def test_thin_structure_stops_at_the_last_point_on_the_same_ray():
     values = np.zeros((11, 15), dtype=np.float32)
     values[5:7, 2:13] = 1