Illustration of how to measure the strength of non-axisymmetric disk structures. The left two panels show the star-cleaned r-band image of NGC 447 and UGC 9476. The dashed blue ellipse in the image of NGC 447 denotes its bar (Appendix B). The right panels show radial profiles of A_tot. The galactocentric radius at which the bulge terminates and the disk starts to dominate (1.5 × R_bul/(1 − ϵ_disk), where ϵ_disk is the disk-averaged ellipticity) is indicated by the dotted line. The bar radius is indicated by the dashed line for NGC 447. The R_90%, enclosing the majority of structure, is indicated by the solid line. We compute s_disk as the mean A_tot over the disk-dominated region between 1.5 × R_bul/(1 − ϵ_disk) and R_90%, and define the strength of non-axisymmetric disk structure as 2 + log s_disk. The disk-dominated region for barred galaxies contains spirals and bars, but that for unbarred galaxies contains only spirals.