Log2

def open_domain_to_normalized_log2(
    in_od,
    in_middle_grey=0.18,
    minimum_ev=-6.0,
    maximum_ev=+7.0
):
    total_exposure = maximum_ev - minimum_ev

    in_od = numpy.asarray(in_od)
    in_od[in_od <= 0.0] = numpy.finfo(numpy.float).eps

    output_log = numpy.clip(
        numpy.log2(in_od / in_middle_grey),
        minimum_ev,
        maximum_ev
    )

    return as_numeric((output_log - minimum_ev) / total_exposure)


# Convert normalised log value to scene referred linear value.
def calculate_log_to_sr(
    in_log_norm,
    sr_middle_grey=base_middle_grey,
    minimum_ev=base_dr_minimum_ev,
    maximum_ev=base_dr_maximum_ev
):
    in_log_norm = numpy.asarray(in_log_norm)

    in_log_norm = numpy.clip(in_log_norm, 0., 1.) * (
        maximum_ev - minimum_ev) + minimum_ev

    return as_numeric(numpy.power(2., in_log_norm) * sr_middle_grey)