Simulation of the underestimation (in mag) of the apparent magnitude of the bulge inside R_B (vertical bar) when applying standard bulge-disk decomposition (into a Sérsic model for the bulge and a pure exponential model for the disk) to a galaxy with a centrally SF-quenched disk. The latter is approximated by a modexp profile with cutoff radii ϵ₂ of 0.67, 1.0, and 1.5 (left, central and right panel, respectively; cf. Fig. A.1) and a central surface depression δμ₀ = −2.5 log(1 − ϵ₁) between 0 and 5 mag. The (extrapolated) central surface brightness μ₀ (21.6 mag/▫″) and exponential scale length α (20″) of the disk are identical to those adopted in Fig. 8. The true apparent magnitude m_B of the bulge (abscissa) varies between 14.27 mag (the value for the Sérsic profile in Fig. 8) and ∼18 mag. Contours go from 0.5 mag to 9 mag in increments of 0.5 mag.