code: def brightness(x, gamma=1, gain=1, is_random=False):
      
      if is_random:
          gamma = np.random.uniform(1 - gamma, 1 + gamma)
      x = exposure.adjust_gamma(x, gamma, gain)
      return x
docs: Change the brightness of a single image, randomly or non-randomly.
  
      Parameters
      -----------
      x : numpy.array
          An image with dimension of [row, col, channel] (default).
      gamma : float
          Non negative real number. Default value is 1.
              - Small than 1 means brighter.
              - If `is_random` is True, gamma in a range of (1-gamma, 1+gamma).
      gain : float
          The constant multiplier. Default value is 1.
      is_random : boolean
          If True, randomly change brightness. Default is False.
  
      Returns
      -------
      numpy.array
          A processed image.
  
      References
      -----------
      - `skimage.exposure.adjust_gamma <http://scikit-image.org/docs/dev/api/skimage.exposure.html>`__
      - `chinese blog <http://www.cnblogs.com/denny402/p/5124402.html>`__