Radial profiles of the logarithmic extinction coefficient c(Hβ) (top), electron temperature T_e (middle), and electronic density n_e (bottom) in the halo of IC 418 (black lines) overlaid by the radial profile of the [O III] λ5007 emission line presented in Fig. 3 (dashed red line). The radial range where the estimates of these physical parameters are found to be reliable is shown with a solid black line and its respective error bars, whereas regions where they become notably uncertain are indicated by thin, dashed black lines.