Modelled effect of scattered light on the filament parameters derived from MIR observations. The filament column density is N(H₂) = 10²⁴ cm⁻², and it is illuminated by an isotropic radiation field and a foreground point source. The blue curves correspond to the case of χ = 1 for the isotropic component and the point source with the nominal luminosity. The cyan and red curves show, respectively, the results when both radiation-field components are scaled by a factor of 20 or 100. The dashed black lines show the correct values of the parameters.