Spectra of three typical H ii regions for two different galaxies, NGC 628 (left panels), and UGC 1081 (right panels). The panels correspond, from top to bottom, to the brightest, average and faintest H ii regions with good quality data for each particular object. The spectral range shows all the emission lines analysed in this article. From top to bottom: each panel shows the integrated spectra of the considered H ii region (solid-black), together with the best model for the underlying stellar population (solid-red), and the pure-gas spectra (solid-blue). The two boxes show a zoom of the same plots at the Hβ and Hα wavelength range.