Implement invert function

skimage/util/__init__.py

@@ -7,6 +7,7 @@ from .apply_parallel import apply_parallel
 from .arraypad import pad, crop
 from ._regular_grid import regular_grid
 from .unique import unique_rows
+from .invert import invert
 
 
 __all__ = ['img_as_float',
@@ -22,4 +23,5 @@ __all__ = ['img_as_float',
            'random_noise',
            'regular_grid',
            'apply_parallel',
+           'invert',
            'unique_rows']

skimage/util/invert.py

@@ -0,0 +1,33 @@
+import numpy as np
+from .dtype import dtype_limits
+
+
+def invert(image):
+    """Invert an image.
+
+    Substract the image to the maximum value allowed by the dtype maximum.
+
+    Parameters
+    ----------
+    image : ndarray
+        The input image.
+
+    Returns
+    -------
+    invert : ndarray
+        Inverted image.
+
+    Examples
+    --------
+    >>> img = np.array([[100, 0, 200],
+    ...			[0,  50, 0],
+    ...			[30,  0, 255]], np.uint8)
+    >>> invert(img)
+    array([[155, 255,  55],
+           [255, 205, 255],
+           [225, 255,   0]], dtype=uint8)
+    """
+    if image.dtype == 'bool':
+        return ~image
+    else:
+        return dtype_limits(image)[1] - image

skimage/util/tests/test_invert.py

@@ -0,0 +1,45 @@
+import numpy as np
+from numpy.testing import assert_array_equal
+from skimage import dtype_limits
+from skimage.util import invert
+
+
+def test_invert_bool():
+    dtype = 'bool'
+    image = np.zeros((3, 3), dtype=dtype)
+    image[1, :] = dtype_limits(image)[1]
+    expected = np.zeros((3, 3), dtype=dtype) + dtype_limits(image)[1]
+    expected[1, :] = 0
+    result = invert(image)
+    assert_array_equal(expected, result)
+
+def test_invert_uint8():
+    dtype = 'uint8'
+    image = np.zeros((3, 3), dtype=dtype)
+    image[1, :] = dtype_limits(image)[1]
+    expected = np.zeros((3, 3), dtype=dtype) + dtype_limits(image)[1]
+    expected[1, :] = 0
+    result = invert(image)
+    assert_array_equal(expected, result)
+
+def test_invert_bool():
+    dtype = 'int8'
+    image = np.zeros((3, 3), dtype=dtype)
+    image[1, :] = dtype_limits(image)[1]
+    expected = np.zeros((3, 3), dtype=dtype) + dtype_limits(image)[1]
+    expected[1, :] = 0
+    result = invert(image)
+    assert_array_equal(expected, result)
+
+def test_invert_bool():
+    dtype = 'float64'
+    image = np.zeros((3, 3), dtype=dtype)
+    image[1, :] = dtype_limits(image)[1]
+    expected = np.zeros((3, 3), dtype=dtype) + dtype_limits(image)[1]
+    expected[1, :] = 0
+    result = invert(image)
+    assert_array_equal(expected, result)
+
+
+if __name__ == '__main__':
+    np.testing.run_module_suite()