Stellar mass surface density (Σ_star) as a function of the r-band average surface brightness within the effective radius (). The LSBs and HSBs are marked as blue open circles and green crosses, respectively. The black dashed line and the black circles mark the median distribution of our sample (the error bars are the median absolute deviation). The mean uncertainty of and Σ_star is 0.03 mag arcsec⁻² and 0.07 M_⊙ kpc⁻², respectively. The brown squares are the HRS sample from Cortese et al. (2012a), and the brown dashed line and squares are their median distribution. The black dash-dotted line and the gray shaded region are the linear best-fit and 3σ scatter of our sample, respectively. The black open circles around some sources are the 3σ outliers of the best-fit line. The three black dotted lines correspond to the expected relation between Σ_star and based on fixed fiducial mass-to-light ratios of 1/3, 1, and 3 M_⊙/L_⊙ (Chamba et al. 2022), as discussed in Sect. 4.