old_contents: from skimage.filter import canny
  
  from .overlayplugin import OverlayPlugin
  from ..widgets import Slider, ComboBox
  
  
  class CannyPlugin(OverlayPlugin):
  
      name = 'Canny Filter'
  
      def __init__(self, *args, **kwargs):
          super(CannyPlugin, self).__init__(image_filter=canny, **kwargs)
  
          self.add_widget(Slider('sigma', 0, 5, update_on='release'))
          self.add_widget(Slider('low threshold', 0, 255, update_on='release'))
          self.add_widget(Slider('high threshold', 0, 255, update_on='release'))
          self.add_widget(ComboBox('color', self.color_names, ptype='plugin'))
  
new_contents: from skimage.filter import canny
  
  from .overlayplugin import OverlayPlugin
  from ..widgets import Slider, ComboBox
  
  
  class CannyPlugin(OverlayPlugin):
      """Canny filter plugin to show edges of an image."""
  
      name = 'Canny Filter'
  
      def __init__(self, *args, **kwargs):
          super(CannyPlugin, self).__init__(image_filter=canny, **kwargs)
  
          self.add_widget(Slider('sigma', 0, 5, update_on='release'))
          self.add_widget(Slider('low threshold', 0, 255, update_on='release'))
          self.add_widget(Slider('high threshold', 0, 255, update_on='release'))
          self.add_widget(ComboBox('color', self.color_names, ptype='plugin'))
  
subject: Add class docstring