Add a helper function to check for low contrast

Add a helper function to check for low contrast

Add a check for low contrast when using imsave

Use the low contrast helper in imshow and make sure warnings are always shown

Clean up parameter names and add doctests

Remove unnecessary warning context

Remove unnecessary warning context

Add dtype ranges for 64bit types

Update tests with new warnings

Fix doctest logic

Fix doctest logic

Add a low contrast test with multiple dtypes

Fix check for color images

Fix color check again

Add support for int32 types

Relax assertion for 32bit builds

Add a low contrast test with multiple dtypes

Add a low contrast test with multiple dtypes

Fix check for color images

Fix color check again

Add support for int32 types

skimage/io/_plugins/matplotlib_plugin.py

@@ -2,7 +2,9 @@ from collections import namedtuple
 import numpy as np
 import warnings
 import matplotlib.pyplot as plt
-from skimage.util import dtype as dtypes
+from ...util import dtype as dtypes
+from ...exposure import is_low_contrast
+from ..._shared._warnings import all_warnings
 
 
 _default_colormap = 'gray'
@@ -49,7 +51,7 @@ def _get_image_properties(image):
     out_of_range_float = (np.issubdtype(image.dtype, np.float) and
                           (immin < lo or immax > hi))
     low_dynamic_range = (immin != immax and
-                         (float(immax - immin) / (hi - lo)) < (1. / 255))
+                         is_low_contrast(image))
     unsupported_dtype = image.dtype not in dtypes._supported_types
 
     return ImageProperties(signed, out_of_range_float,
@@ -72,8 +74,8 @@ def _raise_warnings(image_properties):
         warnings.warn("Low image dynamic range; displaying image with "
                       "stretched contrast.")
     if ip.out_of_range_float:
-        warnings.warn("Float image out of standard range; displaying image "
-                      "with stretched contrast.")
+        warnings.warn("Float image out of standard range; displaying "
+                      "image with stretched contrast.")
 
 
 def _get_display_range(image):