a) Radial profiles of NGC 6946 in surface brightness (Jy) as a function of distance from the center of the galaxy (arcsec). Error bars are inferred from the background measurements reported in Table 2 and from the number of pixels at in the ellipses at each radius. b) Ratio of radial profiles of the different maps over the radial profile of the reference map obtained without compression. Radial profiles are obtained from the maps in Fig. 4. Acronyms refer to Fig. 4.