Single-scale masking of filaments (Sect. 2.4). The images of spatial scales from Fig. 4 are shown here exactly on the intensity threshold for detection of filaments, and all lower level signals were set to zero. The simulated filament is clearly visible on all scales, as is the abundant contamination of the images by noise. Noise-free black zones that appear to surround the filament are the consequence of the negative areas seen in Figs. 4 and 6.