title: Updating bqplot image widget
body: <p>I'm working on a project that uses ipywidgets and bqplot to display and interact with an image. 
  Using ipywidgets and open cv I can modify an image, save it and update the value of the widget. But I also need the on_click_element aspect of bqplot, so I use the widget from the last one. I still have problems figuring out how to do the same thing with the widget in bqplot. </p>
  
  <p>I would like to avoid to redraw the hole thing, but if needed it would have to close and redraw only the widget image since this is part of a bigger set of widgets. For example I would like to binarize the image using an arbitrary treshold.</p>
  
  <p>From here I got the information on how to use the bqplot image widget: <a href="https://github.com/bqplot/bqplot/blob/master/examples/Marks/Object%20Model/Image.ipynb" rel="nofollow noreferrer">https://github.com/bqplot/bqplot/blob/master/examples/Marks/Object%20Model/Image.ipynb</a></p>
  
  <p>I use something very similar to this to create the widget that I display. </p>
  
  <pre><code>from IPython.display import display
  import ipywidgets as widgets
  import bqplot as bq
  
  with open('chelsea.png', 'rb') as f:
      raw_image = f.read()
  
  ipyimage = widgets.Image(value=raw_image, format='png')
  x_sc = bq.LinearScale()
  y_sc = bq.LinearScale()
  bq_image = bq.Image(image=ipyimage, scales={'x':x_sc, 'y':y_sc})
  img_ani = bq.Figure(marks=[bq_image], animation_duration=400)
  display(img_ani)
  </code></pre>
  
  <p>After this I can't update the figure without redrawing the hole thing.
  Any ideas?</p>
  
  <p>jupyter 5.7.8, 
  ipython 7.5.0,
  ipywidgets 7.5.1,
  bqplot 0.12.10</p>