Radial profiles of surface brightness μ (top panel, with linear radial scale), and PA and ellipticity (middle and bottom panels, with logarithmic radial scale) as derived from ellipse fitting to the SST 3.6-μm image of the complete disc of M100. The μ profile has been calculated with fixed PA = 30° and ε= 0.149. Exponential scalelength fits are indicated for the bulge (blue) and disc (red), where the latter was fitted between radii of 35 and 150 arcsec. The two parts of the bar can be clearly seen as distinct rises and falls in the ellipticity profile.