Top: Surface brightness profiles and color profiles extracted by AutoProf as described in the text for IC 342 (left panel) and NGC 6822 (right). Upper panel: SB radial profiles for I_E, Y_E, J_E, and H_E . The four bands are shown as purple, blue, green, and red curves for I_E, Y_E, J_E, and H_E, respectively. The 1σ SB limits from AutoProf (not rescaled to 100 arcsec² regions) in units of mag arcsec^-2 are shown as dashed horizontal lines, with colors corresponding to the Euclid bands. The fluxes have been corrected for foreground extinction (see Sect. 4.1); the uncorrected I_E profile is shown as a dotted (purple) curve in the top panel. Middle and bottom: I_E - H_E and Y_E - H_E radial color profiles. The top axis corresponds to galactocentric radii in units of arcsec, and the bottom in units of kpc. The mean I_E - H_E color over typically a factor of 100 in radius is shown as a horizontal dashed line in the middle panel; the light gray rectangular regions illustrate the full spread in model colors (see Fig. 7) and the dark gray one the standard deviation about the mean of the models. The mean galaxy I_E - H_E with its standard deviation is also shown as a gray rectangular region in Fig. 7.