@staticmethod
def vari_calc(img, scale_factor=10000):
    """ Visible Atmospherically Resistant Index"""
    return img.select(['RED']).subtract(img.select(['GREEN'])).divide(img.
        select(['RED']).add(img.select(['GREEN'])).subtract(img.select([
        'BLUE']))).select([0], ['VARI']).multiply(scale_factor).toInt16()
