Histograms of extracted filament parameters for simulated observations. The first three columns show the recovered central optical depth relative to the true value, τ/τ₀, and the parameters R and p. The last column contains the FWHM values computed from the Plummer parameters. In frames (a)-(h), I^fg is estimated with Eq. (8), in frames (i)-(p) simply based on the minimum observed value. The noise values are 0.2 in frames (a)-(d) and (i)-(l) and 0.75 in frames (e)-(h) and m-p. In each frame, we overplot ten histograms. Each of the individual histograms corresponds one random error in the I^ext value and contains 640 realisations of filament profiles with random observational errors.