Extending ImageSequence reader when only imageio (but not skimage/matplotlib) is installed

pims/image_reader.py

@@ -12,20 +12,24 @@
     from skimage.io import imread
 except ImportError:
     try:
-        from matplotlib.pyplot import imread
-        # imread() works differently between scikit-image and matplotlib.
-        # We don't require users to have scikit-image, 
-        # but if we fall back to matplotlib, make sure the user 
-        # is aware of the consequences.
-        ski_preferred = ("PIMS image_reader.py could not find scikit-image. "
-                 "Falling back to matplotlib's imread(), which uses floats "
-                 "instead of integers. This may break your scripts. \n"
-                 "(To ignore this warning, include the line "
-                 '"warnings.simplefilter("ignore", RuntimeWarning)" '
-                 "in your script.)")
-        warnings.warn(RuntimeWarning(ski_preferred))
+        from imageio import imread
     except ImportError:
-        imread = None
+        try:
+            from matplotlib.pyplot import imread
+            # imread() works differently between scikit-image and matplotlib.
+            # We don't require users to have scikit-image,
+            # but if we fall back to matplotlib, make sure the user
+            # is aware of the consequences.
+            ski_preferred = ("PIMS image_reader.py could not find either "
+                    "scikit-image or imageio installed. "
+                    "Falling back to matplotlib's imread(), which uses floats "
+                    "instead of integers. This may break your scripts. \n"
+                    "(To ignore this warning, include the line "
+                    '"warnings.simplefilter("ignore", RuntimeWarning)" '
+                    "in your script.)")
+            warnings.warn(RuntimeWarning(ski_preferred))
+        except ImportError:
+            imread = None
 
 
 class ImageReader(FramesSequence):

pims/image_sequence.py

@@ -27,9 +27,12 @@
     has_skimage = True
 except ImportError:
     try:
-        from matplotlib.pyplot import imread
+        from imageio import imread
     except ImportError:
-        imread = None
+        try:
+            from matplotlib.pyplot import imread
+        except ImportError:
+            imread = None
 
 
 class ImageSequence(FramesSequence):

pims/tests/test_common.py

@@ -62,6 +62,17 @@ def _skip_if_no_skimage():
         raise nose.SkipTest('skimage not installed. Skipping.')
 
 
+def _skip_if_no_skimage_or_matplotlib():
+    try:
+        import skimage
+    except ImportError:
+        try:
+            import matplotlib
+        except ImportError:
+            raise nose.SkipTest('Test requires either matplotlib or'
+                                ' scikit-image. Skipping.')
+
+
 def _skip_if_no_PIL():
     import pims.tiff_stack
     if not pims.tiff_stack.PIL_available():

pims/tests/test_imseq.py

@@ -13,7 +13,8 @@
 
 from pims.tests.test_common import (_image_series,
                                     clean_dummy_png, save_dummy_png,
-                                    _skip_if_no_skimage, _skip_if_no_imread)
+                                    _skip_if_no_skimage, _skip_if_no_imread,
+                                    _skip_if_no_skimage_or_matplotlib)
 
 path, _ = os.path.split(os.path.abspath(__file__))
 path = os.path.join(path, 'data')
@@ -107,7 +108,7 @@ def tearDown(self):
 
 class TestImageSequenceNaturalSorting(_image_series, unittest.TestCase):
     def setUp(self):
-        _skip_if_no_imread()
+        _skip_if_no_skimage_or_matplotlib()
         self.filepath = os.path.join(path, 'image_sequence')
         self.filenames = ['T76S3F1.png', 'T76S3F20.png',
                           'T76S3F3.png', 'T76S3F4.png',