BUG: division by zero for small arrays in iradon

skimage/transform/radon_transform.py

@@ -135,7 +135,7 @@ def iradon(radon_image, theta=None, output_size=None,
     img = radon_image.copy()
     # resize image to next power of two for fourier analysis
     # speeds up fourier and lessens artifacts
-    order = max(64, 2 ** np.ceil(np.log(2 * n) / np.log(2)))
+    order = max(64., 2 ** np.ceil(np.log(2 * n) / np.log(2)))
     # zero pad input image
     img.resize((order, img.shape[1]))
     # construct the fourier filter

skimage/transform/tests/test_radon_transform.py

@@ -30,6 +30,9 @@ def test_radon_iradon():
     reconstructed = iradon(radon(image), filter="ramp", interpolation="nearest")
     delta = np.mean(abs(image - reconstructed))
     assert delta < 0.05
+    size = 20
+    image = np.tri(size) + np.tri(size)[::-1]
+    reconstructed = iradon(radon(image), filter="ramp", interpolation="nearest")
    
 def test_iradon_angles():
     """