Reddening constant maps of HS 0128+2832, HS 0837+4717, and Mrk 930 from left to right. The solid line contours are those described in Fig. 3. The histogram plots above represent the distribution of the extinction in different regions: dark blue bars represent the spaxels in Region 1 (spaxels with a F(Hα) larger than 25% of the maximum), light blue bars, in Region 2 (spaxels with F(Hα) larger than 12.5% of the maximum), and white bars, Region 3 (all the spaxels in the observed field with S/N).