Upper panel: subtraction of the best-fitting stellar SED computed with Starlight with two different SSP libraries (BC03 and MILES; blue and magenta, respectively) from an observed sisp spectrum extracted from an off-nucleus region of a CALIFA ETG. The fit residuals are comparatively small, on the order of 1–2σ of the continuum in the blue spectral range, but they are systematic. lower panel: the same spectrum after rectification of the rest-continuum.