def sb_to_i(sb, m_0=27, a_pix=1):
    """ Convert a given surface brightness to an intensity.

    Args:
        sb (float): Surface brightness
        m_0 (float): Zero-point magnitude
        a_pix (float): Area of a pixel (in arc seconds squared)

    Returns:
        Intensity value for the given surface brightness.
    """
    exponential = (sb - m_0) / -2.5
    return a_pix * (10 ** exponential)