Bias on the r-band magnitude (bottom panel) and half-light radius (top panel) from the fit of a Sérsic profile to the r-band images of the set of simulated galaxies shown in Fig. 4, as a function of the ratio between the light-weighted radius of the spiral arms and the half-light radius of the smooth surface brightness component. All of the simulated galaxies have a spiral-arm-to-total ratio of f_spi = 0.10 and a smooth component with n = 4 and R_e, smo = 2.52″, and the images have HSC-like properties.