Merge pull request #1828 from stefanv/radon_circle_warn

radon transform: ignore values outside circle

skimage/transform/radon_transform.py

@@ -20,6 +20,7 @@ from scipy.interpolate import interp1d
 from ._warps_cy import _warp_fast
 from ._radon_transform import sart_projection_update
 from .. import util
+from warnings import warn
 
 
 __all__ = ["radon", "iradon", "iradon_sart"]
@@ -49,11 +50,6 @@ def radon(image, theta=None, circle=False):
         at the pixel index ``radon_image.shape[0] // 2`` along the 0th
         dimension of ``radon_image``.
 
-    Raises
-    ------
-    ValueError
-        If called with ``circle=True`` and ``image != 0`` outside the inscribed
-        circle
     """
     if image.ndim != 2:
         raise ValueError('The input image must be 2-D')
@@ -67,8 +63,8 @@ def radon(image, theta=None, circle=False):
                                  + (c1 - image.shape[1] // 2) ** 2)
         reconstruction_circle = reconstruction_circle <= radius ** 2
         if not np.all(reconstruction_circle | (image == 0)):
-            raise ValueError('Image must be zero outside the reconstruction'
-                             ' circle')
+            warn('Radon transform: image must be zero outside the '
+                 'reconstruction circle')
         # Crop image to make it square
         slices = []
         for d in (0, 1):

skimage/transform/tests/test_radon_transform.py

@@ -9,7 +9,7 @@ from skimage.transform import radon, iradon, iradon_sart, rescale
 from skimage.io import imread
 from skimage import data_dir
 from skimage._shared.testing import test_parallel
-
+from skimage._shared._warnings import expected_warnings
 
 PHANTOM = imread(os.path.join(data_dir, "phantom.png"),
                    as_grey=True)[::2, ::2]
@@ -215,7 +215,8 @@ def _random_circle(shape):
 
 def test_radon_circle():
     a = np.ones((10, 10))
-    assert_raises(ValueError, radon, a, circle=True)
+    with expected_warnings(['reconstruction circle']):
+        radon(a, circle=True)
 
     # Synthetic data, circular symmetry
     shape = (61, 79)