Corner plot comparing the reddening value (E(B − V)) measured directly from the data (before and after the correction for DIG contribution) with the values obtained by IZI using the three different grids of models used in the classification algorithm (H II regions, PNe and Shocks). Only the regions belonging to the BPT sample are considered in this plot (see Sect. 6.1). In each plot, the coloured points represent the nebulae we could classify with our algorithm, following the usual convention. Only the points belonging to the grids considered by the specific panel are coloured. The plots on the matrix’s diagonal show regions’ distribution as a function of E(B − V) for each method.