PDFs of the logarithm of the relative values of column density (N∕⟨N⟩); blue lines) and 250μm surface brightness (S(250μm)∕⟨S(250μm)⟩); red lines). Gaussian fits to the column density histograms are shown as dotted black lines. The black histograms are derived from column density that is estimated based on background subtracted surface-brightness data. The grey histograms additionally (mostly on top of the black histograms) include the bias corrections derived from RT models. The fields are arranged in the order of increasing distance (see Table 1).