Add map function for generic SpatialImage

Author: effigies

nibabel/spatialimages.py

@@ -872,3 +872,9 @@ def __getitem__(self):
         raise TypeError("Cannot slice image objects; consider slicing image "
                         "array data with `img.dataobj[slice]` or "
                         "`img.get_data()[slice]`")
+
+
+def mapImage(func, img):
+    """Map a function onto image data"""
+    return img.__class__(func(img.get_data()), img.affine, img.header.copy(),
+                         extra=img.extra.copy())

nibabel/tests/test_spatialimages.py

@@ -13,7 +13,7 @@
 import numpy as np
 
 from ..spatialimages import (Header, SpatialImage, HeaderDataError,
-                             ImageDataError)
+                             ImageDataError, mapImage)
 
 from unittest import TestCase
 
@@ -382,3 +382,9 @@ def test_load_mmap(self):
                 # Check invalid values raise error
                 assert_raises(ValueError, func, param1, mmap='rw')
                 assert_raises(ValueError, func, param1, mmap='r+')
+
+
+def test_mapImage():
+    img = SpatialImage(np.zeros((2, 3, 4)), np.eye(4))
+    assert np.unique(mapImage(lambda x: x + 1, img).get_data()) == \
+        np.array([1.0])