Flux variation gradient diagram of ESO 399-IG20 for aperture. The solid lines delineate the ordinary least square bisector regression model yielding the range of the AGN slope. The dashed lines indicate the interpolated range of host slopes obtained from Sakata et al. (2010) for 11 nearby AGN. The intersection between the host galaxy and AGN slope (red area) gives the host galaxy flux in both bands. The dash-dotted blue lines represent the range of the AGN flux in both filters.