Quality of the derived background presented in Fig. 2. Shown are the relative accuracies of the background obtained by median filtering with respect to the true background ℬ_λ. Only the relevant pixels within the model sources are shown for values limited by the range [−0.3,0.3 ] with linear color coding. In panel a, the minima visible in the centers of some footprints are caused by the absorption of radiation in the central parts of starless cores; the two deepest minima are at levels of −0.7 and −0.6. In panels b and c, the maxima are at levels of 0.8 and 0.7, respectively.