Added test case for warp() when cval out of clipping range

skimage/transform/_geometric.py

@@ -786,6 +786,7 @@ def warp(image, inverse_map=None, map_args={}, output_shape=None, order=1,
     # The spline filters sometimes return results outside [0, 1],
     # so clip to ensure valid data
     clipped = np.clip(mapped, 0, 1)
+
     if mode == 'constant' and not (0 <= cval <= 1):
         clipped[mapped == cval] = cval
 

skimage/transform/tests/test_warps.py

@@ -2,7 +2,8 @@ from numpy.testing import assert_array_almost_equal, run_module_suite
 import numpy as np
 
 from skimage.transform import (warp, homography, fast_homography,
-                               SimilarityTransform, ProjectiveTransform)
+                               SimilarityTransform, ProjectiveTransform,
+                               AffineTransform)
 from skimage import transform as tf, data, img_as_float
 from skimage.color import rgb2gray
 
@@ -74,5 +75,12 @@ def test_swirl():
     assert np.mean(np.abs(image - unswirled)) < 0.01
 
 
+def test_const_cval_out_of_range():
+    img = np.random.randn(100, 100)
+    warped = warp(img, AffineTransform(translation=(10, 10)), cval=-10)
+    assert np.any(warped < 0)
+
+
+
 if __name__ == "__main__":
     run_module_suite()