def brightness(x, gamma=<NUM_LIT:1>, gain=<NUM_LIT:1>, is_random=False):
if is_random:<EOL><INDENT>gamma = np.random.uniform(<NUM_LIT:1> - gamma, <NUM_LIT:1> + gamma)<EOL><DEDENT>x = exposure.adjust_gamma(x, gamma, gain)<EOL>return x<EOL>
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>`__