Parameters of the N-PDFs of contaminated clouds corrected for the contamination through the subtraction of a constant offset given by the peak of the N-PDF of the contaminating structure. The upper plot shows the position of the N-PDF peak on the logarithmic column density scale η relative to the original peak column of the cloud. Consequently a value of 0 represents the correct peak position; a value of 0.5 indicates a 65 % overestimate of the column. The lower plot shows the width of the corrected cloud N-PDF relative to the original cloud N-PDF. On the horizontal axis, we varied the amplitude of the contamination, while on the vertical axis its width relative to the cloud N-PDF width.