code: def get_canvas_image(self):
          
          if self._imgobj is not None:
              return self._imgobj
  
          try:
              # See if there is an image on the canvas
              self._imgobj = self.canvas.get_object_by_tag(self._canvas_img_tag)
              self._imgobj.add_callback('image-set', self._image_set_cb)
  
          except KeyError:
              # add a normalized image item to this canvas if we don't
              # have one already--then just keep reusing it
              NormImage = self.canvas.getDrawClass('normimage')
              interp = self.t_.get('interpolation', 'basic')
  
              # previous choice might not be available if preferences
              # were saved when opencv was being used (and not used now)
              # --if so, default to "basic"
              if interp not in trcalc.interpolation_methods:
                  interp = 'basic'
  
              self._imgobj = NormImage(0, 0, None, alpha=1.0,
                                       interpolation=interp)
              self._imgobj.add_callback('image-set', self._image_set_cb)
  
          return self._imgobj
docs: Get canvas image object.
  
          Returns
          -------
          imgobj : `~ginga.canvas.types.image.NormImage`
              Normalized image sitting on the canvas.