Purely synthetic image, made up of a scale-free background image constructed using the fBm algorithm (panel a; cf. Miville-Deschênes et al. 2003). The embedded synthetic filaments have a lognormal column density contrast distribution in a range between 0.3 <  δ_c <  2 and peak of δ_peak ∼ 0.9. The overall area-filling factor of the filaments is A_fil ∼ 3%. The filaments are of Gaussian profiles with a FWHM ∼0.1 pc at a distance of 140 pc (see text). Panel b: solid black curve shows the power spectrum of the scale-free background image and the synthetic filaments. The logarithmic slope of the power-spectrum is γ ∼ −2.7 ± 0.1. The dashed curve shows the power spectrum of the background image (γ ∼ −2.8). The blue solid line shows the power spectrum of the synthetic filaments. Panel c: residuals between the best power-law fit and the power spectrum data points (triangle symbols) of synthetic cirrus map. The of the residuals between k_min <  k <  1.5 k_fil is 0.03.