Benchmark B₄ extraction of filaments with getsf. The component of filaments ℱ_ƛY is shown in the middle panel for the surface density 𝒟_13″, overlaid with the skeleton 𝒦_k4 (detection significance ξ = 4) obtained from the combined ℱ_DjC on the scales S_​k ≈ 153″, corresponding to the adopted value Y_ƛ = 150″. The left panel displays the skeletons and the footprints Υ_n, with the pixel values equal to the skeleton (filament) number. The right panel shows the detected skeleton of the spiral filament, together with its one-sided normals. The first pixel of the skeleton is at the center, hence the left normals point to the center (red) and the right normals point outward (orange). Square-root color mapping, except the footprints with linear mapping.