Merge pull request #260 from ahojnnes/convert-bool

ENH: Support for boolean dtype conversion.

skimage/util/dtype.py

@@ -1,12 +1,15 @@
 from __future__ import division
 import numpy as np
 
-__all__ = ['img_as_float', 'img_as_int', 'img_as_uint', 'img_as_ubyte']
+__all__ = ['img_as_float', 'img_as_int', 'img_as_uint', 'img_as_ubyte',
+           'img_as_bool']
 
 from .. import get_log
 log = get_log('dtype_converter')
 
-dtype_range = {np.uint8: (0, 255),
+dtype_range = {np.bool_: (False, True),
+               np.bool8: (False, True),
+               np.uint8: (0, 255),
                np.uint16: (0, 65535),
                np.int8: (-128, 127),
                np.int16: (-32768, 32767),
@@ -15,7 +18,8 @@ dtype_range = {np.uint8: (0, 255),
 
 integer_types = (np.uint8, np.uint16, np.int8, np.int16)
 
-_supported_types = (np.uint8, np.uint16, np.uint32,
+_supported_types = (np.bool_, np.bool8,
+                    np.uint8, np.uint16, np.uint32,
                     np.int8, np.int16, np.int32,
                     np.float32, np.float64)
 
@@ -145,6 +149,10 @@ def convert(image, dtype, force_copy=False, uniform=False):
     kind_in = dtypeobj_in.kind
     itemsize = dtypeobj.itemsize
     itemsize_in = dtypeobj_in.itemsize
+
+    if kind == 'b' or kind_in == 'b':
+        return dtype(image)
+
     if kind in 'ui':
         imin = np.iinfo(dtype).min
         imax = np.iinfo(dtype).max
@@ -322,3 +330,26 @@ def img_as_ubyte(image, force_copy=False):
 
     """
     return convert(image, np.uint8, force_copy)
+
+
+def img_as_bool(image, force_copy=False):
+    """Convert an image to boolean format.
+
+    Parameters
+    ----------
+    image : ndarray
+        Input image.
+    force_copy : bool
+        Force a copy of the data, irrespective of its current dtype.
+
+    Returns
+    -------
+    out : ndarray of bool (bool_)
+        Output image.
+
+    Notes
+    -----
+    All non-zero elements are treated as True.
+
+    """
+    return convert(image, np.bool_, force_copy)

skimage/util/tests/test_dtype.py

@@ -1,7 +1,7 @@
 import numpy as np
 from numpy.testing import assert_equal, assert_raises
 from skimage import img_as_int, img_as_float, \
-                    img_as_uint, img_as_ubyte
+                    img_as_uint, img_as_ubyte, img_as_bool
 from skimage.util.dtype import convert
 
 
@@ -86,5 +86,19 @@ def test_copy():
     assert y is x
     assert z is not x
 
+
+def test_bool():
+    img_ = np.zeros((10, 10), np.bool_)
+    img8 = np.zeros((10, 10), np.bool8)
+    img_[1, 1] = True
+    img8[1, 1] = True
+    funcs = (img_as_float, img_as_int, img_as_ubyte, img_as_uint, img_as_bool)
+    for func in funcs:
+        converted_ = func(img_)
+        assert np.sum(converted_) == 1
+        converted8 = func(img8)
+        assert np.sum(converted8) == 1
+
+
 if __name__ == '__main__':
     np.testing.run_module_suite()