code: def redo(self):
          
          self.clear()
  
          tab = self.channel.get_current_image()
          if not isinstance(tab, AstroTable):
              return
  
          # Generate column indices
          self.tab = tab.get_data()
          self._idx = np.arange(len(self.tab))
  
          # Populate combobox with table column names
          self.cols = [self._idxname] + self.tab.colnames
          self.x_col = self._set_combobox(
              'xcombo', self.cols, default=self.settings.get('x_index', 1))
          self.y_col = self._set_combobox(
              'ycombo', self.cols, default=self.settings.get('y_index', 2))
  
          # Automatically plot first two columns
          self.plot_two_columns(reset_xlimits=True, reset_ylimits=True)
docs: This is called when a new image arrives or the data in the
          existing image changes.