old_contents: """
  =====================
  CollectionViewer demo
  =====================
  
  Demo of CollectionViewer for viewing collections of images. This demo uses
  successively darker versions of the same image to fake an image collection.
  
  You can scroll through images with the slider, or you can interact with the
  viewer using your keyboard:
  
  left/right arrows
      Previous/next image in collection.
  number keys, 0--9
      0% to 90% of collection. For example, "5" goes to the image in the
      middle (i.e. 50%) of the collection.
  home/end keys
      First/last image in collection.
  
  """
  import numpy as np
  from skimage import data
  from skimage.viewer import CollectionViewer
  from skimage.transform import build_gaussian_pyramid
  
  
  img = data.lena()
  img_collection = tuple(build_gaussian_pyramid(img))
  
  view = CollectionViewer(img_collection)
  view.show()
  
new_contents: """
  =====================
  CollectionViewer demo
  =====================
  
  Demo of CollectionViewer for viewing collections of images. This demo uses
  the different layers of the gaussian pyramid as image collection.
  
  You can scroll through images with the slider, or you can interact with the
  viewer using your keyboard:
  
  left/right arrows
      Previous/next image in collection.
  number keys, 0--9
      0% to 90% of collection. For example, "5" goes to the image in the
      middle (i.e. 50%) of the collection.
  home/end keys
      First/last image in collection.
  
  """
  import numpy as np
  from skimage import data
  from skimage.viewer import CollectionViewer
  from skimage.transform import build_gaussian_pyramid
  
  
  img = data.lena()
  img_collection = tuple(build_gaussian_pyramid(img))
  
  view = CollectionViewer(img_collection)
  view.show()
  
subject: Update description of collection viewer example