docs: def palettebar(height, length, colormap):
      """Return the channels of a palettebar.
      """
      cbar = np.tile(np.arange(length) * 1.0 / (length - 1), (height, 1))
      cbar = (cbar * (colormap.values.max() + 1 - colormap.values.min())
              + colormap.values.min())
  
      return colormap.palettize(cbar)