Correction for [NII] contamination. Left panels: relation between the [NII]λ6548 + 6583 Å/Hα line ratio (upper panel), the dust attenuation measured using the Balmer decrement A(Hα)_BD (middle panel), and the dust attenuation A(Hα) derived by averaging the Balmer decrement and the far-infrared determinations (see Sect. 3.3; lower panel) and the stellar mass of the selected galaxies. The long-dashed red lines indicate the mean relations derived in this work. Right panels: [NII]λ6548 + 6583 Å/Hα, A(Hα)_BD, and A(Hα) distributions. The hatched red and blue histograms give the distribution of [NII]λ6548 + 6583 Å/Hα, A(Hα)_BD, and A(Hα) derived from the mean scaling relations given in the text and adopted in the Hα flux correction for galaxies without any spectroscopic data.