unwrap: Test wrap_around functionality.

This test is currently failing. Most likely, the axes are swapped.

skimage/exposure/tests/test_unwrap.py

@@ -1,8 +1,12 @@
+from __future__ import print_function, division
+
 import numpy as np
-from numpy.testing import run_module_suite, assert_array_almost_equal
+from numpy.testing import (run_module_suite, assert_array_almost_equal,
+                           assert_almost_equal)
 
 from skimage.exposure import unwrap
 
+
 def test_unwrap2D():
     x, y = np.ogrid[:8, :16]
     phi = 2*np.pi*(x*0.2 + y*0.1)
@@ -47,6 +51,43 @@ def test_unwrap3D_masked():
     s = np.round(phi_unwrapped_masked[0,0,0]/(2*np.pi))
     assert_array_almost_equal(phi + 2*np.pi*s, phi_unwrapped_masked)
 
+
+def check_wrap_around(ndim, axis):
+    # create a ramp, but with the last pixel along axis equalling the first
+    elements = 100
+    ramp = np.linspace(0, 12 * np.pi, elements)
+    ramp[-1] = ramp[0]
+    image = ramp.reshape(tuple([elements if n == axis else 1
+                                for n in range(ndim)]))
+    image_wrapped = np.angle(np.exp(1j * image))
+
+    index_first = tuple([0] * ndim)
+    index_last = tuple([-1 if n == axis else 0 for n in range(ndim)])
+    # unwrap the image without wrap around
+    image_unwrap_no_wrap_around = unwrap(image_wrapped)
+    print('endpoints without wrap_around:',
+          image_unwrap_no_wrap_around[index_first],
+          image_unwrap_no_wrap_around[index_last])
+    # without wrap around, the endpoints of the image should differ
+    assert abs(image_unwrap_no_wrap_around[index_first]
+               - image_unwrap_no_wrap_around[index_last]) > np.pi
+    # unwrap the image with wrap around
+    wrap_around = [n == axis for n in range(ndim)]
+    image_unwrap_wrap_around = unwrap(image_wrapped, wrap_around)
+    print('endpoints with wrap_around:',
+          image_unwrap_wrap_around[index_first],
+          image_unwrap_wrap_around[index_last])
+    # with wrap around, the endpoints of the image should be equal
+    assert_almost_equal(image_unwrap_wrap_around[index_first],
+                        image_unwrap_wrap_around[index_last])
+
+
+def test_wrap_around():
+    for ndim in (2, 3):
+        for axis in range(ndim):
+            yield check_wrap_around, ndim, axis
+
+
 def unwrap_plots():
 
     x, y = np.ogrid[:32, :32]