new_contents: from skimage import data
  from skimage.filter import canny
  
  from skimage.viewer import ImageViewer
  from skimage.viewer.widgets import Slider
  from skimage.viewer.plugins.overlayplugin import OverlayPlugin
  
  
  image = data.camera()
  # Note: ImageViewer must be called before Plugin b/c it starts the event loop.
  viewer = ImageViewer(image)
  # 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')
  # Finally, attach the plugin to the image viewer.
  viewer += plugin
  viewer.show()
  
subject: Add example of adding widgets to plugin