def evi(b2, b4, b8):
    """
    Enhanced Vegetation Index (Huete et al., 2002).

    .. math:: EVI = 2.5 * (b8 - b4) / (b8 + 6 * b4 - 7.5 * b2 + 1)

    :param b2: Blue.
    :type b2: numpy.ndarray or float
    :param b4: Red.
    :type b4: numpy.ndarray or float
    :param b8: NIR.
    :type b8: numpy.ndarray or float

    :returns EVI: Index value

    .. Tip::

        Huete, A., Didan, K., Miura, T., Rodriguez, E. P., Gao, X., \
        Ferreira, L. G. 2002. Overview of the radiometric and biophysical \
        performance of the MODIS vegetation indices. Remote Sensing of \
        Environment 83(1-2), 195-213. doi:10.1016/S0034-4257(02)00096-2.

    """

    EVI = 2.5 * (b8 - b4) / (b8 + 6 * b4 - 7.5 * b2 + 1)
    return EVI