def tvi(b3, b4, b6):
    """
    Transformed Vegetation Index (Broge and Leblanc, 2001).

    .. math:: TVI = 0.5 * (120 * (b6 - b3) - 200 * (b4 - b3))

    :param b3: Green.
    :type b3: numpy.ndarray or float
    :param b4: Red.
    :type b4: numpy.ndarray or float
    :param b6: Red-edge 2.
    :type b6: numpy.ndarray or float

    :returns TVI: Index value

    .. Tip::

        Broge, N.H., Leblanc, E., 2001. Comparing prediction power and \
        stability ofbroadband and hyperspectral vegetation indices for \
        estimation of green leaf area index and canopy chlorophyll density. \
        Remote Sensing of Environment 76, 156-172. \
        doi:10.1016/S0034-4257(00)00197-8.
    """

    TVI = 0.5 * (120 * (b6 - b3) - 200 * (b4 - b3))
    return TVI