Add reset and compare to novice module

- Reset restores the image to the original.
- Compare displays the original and the modified image side-by-side.

skimage/io/_io.py

@@ -157,7 +157,7 @@ def imshow(arr, plugin=None, **plugin_args):
 
 
 def imshow_collection(ic, plugin=None, **plugin_args):
-    """Display an image.
+    """Display a collection of images.
 
     Parameters
     ----------

skimage/io/_plugins/matplotlib_plugin.py

@@ -171,7 +171,7 @@ def imshow_collection(ic, *args, **kwargs):
     """
     fig, axes = plt.subplots(1, len(ic))
     for n, image in enumerate(ic):
-        kwargs['axis'] = axes[n]
+        kwargs['ax'] = axes[n]
         imshow(image, *args, **kwargs)
 
 

skimage/novice/__init__.py

@@ -56,9 +56,9 @@ Changing `size` resizes the picture.
 
 >>> picture.size = (45, 30)
 
-We can preview the changes we made to the picture with our earlier command:
+We can preview the changes we made to the picture with the ``compare`` command:
 
->>> picture.show()  # doctest: +SKIP
+>>> picture.compare()  # doctest: +SKIP
 
 You can iterate over pixels, which have RGB values between 0 and 255,
 and know their location in the picture.
@@ -88,6 +88,13 @@ True
 >>> picture.modified
 False
 
+An image can also be restored to its original state after modification:
+
+>>> picture[0:20, 0:20] = (0, 0, 0)
+>>> picture.compare()  # doctest: +SKIP
+>>> picture.reset()
+>>> picture.compare()  # doctest: +SKIP
+
 """
 from ._novice import Picture, open, colors, color_dict
 

skimage/novice/_novice.py

@@ -7,6 +7,7 @@ from .. import io, img_as_ubyte
 from ..transform import resize
 from ..color import color_dict
 from ..io.util import file_or_url_context, is_url
+from ..io.collection import ImageCollection
 
 import six
 from six.moves.urllib import request
@@ -305,6 +306,7 @@ class Picture(object):
     def array(self, array):
         self._array = array
         self._xy_array = array_to_xy_origin(array)
+        self._array_backup = self._array.copy()
 
     @property
     def xy_array(self):
@@ -329,6 +331,12 @@ class Picture(object):
         self._path = os.path.abspath(path)
         self._format = imghdr.what(path)
 
+    def reset(self):
+        """Reset image to its original state, removing modifications.
+
+        """
+        self.array = self._array_backup
+
     @property
     def path(self):
         """The path to the picture."""
@@ -388,6 +396,13 @@ class Picture(object):
         io.imshow(self.array)
         io.show()
 
+    def compare(self):
+        """Compare the image to its unmodified version."""
+        images = [self._array_backup, self.array]
+        ic = ImageCollection([0, 1], load_func=lambda x: images[x])
+        io.imshow_collection(images)
+        io.show()
+
     def _makepixel(self, x, y):
         """Create a Pixel object for a given x, y location."""
         rgb = self.xy_array[x, y]

skimage/novice/tests/test_novice.py

@@ -135,8 +135,18 @@ def test_modified_on_set_pixel():
     assert pic.modified
 
 
+def test_reset():
+    pic = novice.Picture(SMALL_IMAGE_PATH)
+    v = pic[0, 0]
+    pic[0, 0] = (1, 1, 1)
+    pic.reset()
+    assert_equal(pic[0, 0], v)
+
+
 def test_update_on_save():
     pic = novice.Picture(array=np.zeros((3, 3, 3)))
+    pic[0, 0] = (255, 255, 255)  # prevent attempting to save low-contrast image
+
     with all_warnings():  # precision loss
         pic.size = (6, 6)
     assert pic.modified