Comparison of central disk surface brightnesses of 20 galaxies derived from a single component and a combination of two-component fitting, respectively. The top panel (a) shows the comparison of the B-band central disk surface brightnesses derived by a single exponential fitting, ﹩{{\mu }_{0}}﹩(B) (exp), with those derived by a two-component exponential and Sérsic (exp + Sérsic) profile fitting ﹩{{\mu }_{0}}﹩(B)(exp+Sérsic). The bottom panel (b) shows the differences of ﹩{{\mu }_{0}}﹩(B)(exp+Sérsic) from ﹩{{\mu }_{0}}﹩(B) (exp) versus the bulge-to-total luminosity ratio (B/T). The surface brightness is given in units of mag arcsec⁻².