Change default Slider update_on value to 'release'

Image filtering is usually slow, so updating on move was usually a bad idea.

skimage/viewer/widgets/core.py

@@ -90,12 +90,12 @@ class Slider(BaseWidget):
         is typically set when the widget is added to a plugin.
     orientation : {'horizontal' | 'vertical'}
         Slider orientation.
-    update_on : {'move' | 'release'}
+    update_on : {'release' | 'move'}
         Control when callback function is called: on slider move or release.
     """
     def __init__(self, name, low=0.0, high=1.0, value=None, value_type='float',
                  ptype='kwarg', callback=None, max_edit_width=60,
-                 orientation='horizontal', update_on='move'):
+                 orientation='horizontal', update_on='release'):
         super(Slider, self).__init__(name, ptype, callback)
 
         if value is None:

viewer_examples/plugins/canny_simple.py

@@ -12,9 +12,9 @@ image = data.camera()
 # You can create a UI for a filter just by passing a filter function...
 plugin = OverlayPlugin(image_filter=canny)
 # ... and adding widgets to adjust parameter values.
-plugin += Slider('sigma', 0, 5, update_on='release')
-plugin += Slider('low threshold', 0, 255, update_on='release')
-plugin += Slider('high threshold', 0, 255, update_on='release')
+plugin += Slider('sigma', 0, 5)
+plugin += Slider('low threshold', 0, 255)
+plugin += Slider('high threshold', 0, 255)
 # ... and we can also add buttons to save the overlay:
 plugin += SaveButtons(name='Save overlay to:')
 

viewer_examples/plugins/collection_plugin.py

@@ -24,7 +24,7 @@ def autolevel(image, disk_size):
 img_collection = [data.camera(), data.coins(), data.text()]
 
 plugin = Plugin(image_filter=autolevel)
-plugin += Slider('disk_size', 2, 8, value_type='int', update_on='release')
+plugin += Slider('disk_size', 2, 8, value_type='int')
 plugin.name = "Autolevel"
 
 viewer = CollectionViewer(img_collection)

viewer_examples/plugins/median_filter.py

@@ -10,7 +10,7 @@ image = data.coins()
 viewer = ImageViewer(image)
 
 plugin = Plugin(image_filter=median_filter)
-plugin += Slider('radius', 2, 10, value_type='int', update_on='release')
+plugin += Slider('radius', 2, 10, value_type='int')
 plugin += SaveButtons()
 plugin += OKCancelButtons()
 

viewer_examples/plugins/probabilistic_hough.py

@@ -34,8 +34,8 @@ canny_viewer += canny_plugin
 hough_plugin = OverlayPlugin(image_filter=hough_lines)
 hough_plugin.name = 'Hough Lines'
 
-hough_plugin += Slider('line length', 0, 100, update_on='release')
-hough_plugin += Slider('line gap', 0, 20, update_on='release')
+hough_plugin += Slider('line length', 0, 100)
+hough_plugin += Slider('line gap', 0, 20)
 
 # Passing a plugin to a viewer connects the output of the plugin to the viewer.
 hough_viewer = ImageViewer(canny_plugin)