code: def add_highlight_area(self, mask, label=None, col=0):
          
          patch = mask * np.ones(mask.shape) * 0.9
          cmap = self.conf.cmap[col]
          area = self.axes.contour(patch, cmap=cmap, levels=[0, 1])
          self.conf.highlight_areas.append(area)
          col = None
          if hasattr(cmap, '_lut'):
              rgb  = [int(i*240)^255 for i in cmap._lut[0][:3]]
              col  = '#%02x%02x%02x' % (rgb[0], rgb[1], rgb[2])
  
          if label is not None:
              def fmt(*args, **kws): return label
              self.axes.clabel(area, fontsize=9, fmt=fmt,
                               colors=col, rightside_up=True)
  
          if col is not None:
              for l in area.collections:
                  l.set_color(col)
  
          self.canvas.draw()
docs: add a highlighted area -- outline an arbitrarily shape --
          as if drawn from a Lasso event.
  
          This takes a mask, which should be a boolean array of the
          same shape as the image.