Merge pull request #1183 from jni/warn-single-labels

Warn when single int label of 1 is passed to remove_small_objects

skimage/morphology/misc.py

@@ -1,5 +1,6 @@
 import numpy as np
 import functools
+import warnings
 import scipy.ndimage as nd
 from .selem import _default_selem
 
@@ -128,6 +129,10 @@ def remove_small_objects(ar, min_size=64, connectivity=1, in_place=False):
                          "relabeling the input with `scipy.ndimage.label` or "
                          "`skimage.morphology.label`.")
 
+    if len(component_sizes) == 2:
+        warnings.warn("Only one label was provided to `remove_small_objects`. "
+                      "Did you mean to use a boolean array?")
+
     too_small = component_sizes < min_size
     too_small_mask = too_small[ccs]
     out[too_small_mask] = 0

skimage/morphology/tests/test_misc.py

@@ -1,5 +1,6 @@
 import numpy as np
-from numpy.testing import assert_array_equal, assert_equal, assert_raises
+from numpy.testing import (assert_array_equal, assert_equal, assert_raises,
+                           assert_warns)
 from skimage.morphology import remove_small_objects
 
 test_image = np.array([[0, 0, 0, 1, 0],
@@ -55,6 +56,13 @@ def test_uint_image():
     assert_array_equal(observed, expected)
 
 
+def test_single_label_warning():
+    image = np.array([[0, 0, 0, 1, 0],
+                      [1, 1, 1, 0, 0],
+                      [1, 1, 1, 0, 0]], int)
+    assert_warns(UserWarning, remove_small_objects, image, min_size=6)
+
+
 def test_float_input():
     float_test = np.random.rand(5, 5)
     assert_raises(TypeError, remove_small_objects, float_test)