frequency op• Data kinds: voxel → voxel
• Call: import fullseye as fs; fs.ledger.vol_fft_lowpass(vol, cutoff, spacing=None) (to call the implementation directly, import volfreq; volfreq.vol_fft_lowpass(vol, cutoff, spacing=None); from the registry, ops3d.get("vol_fft_lowpass"))
Gaussian low-pass: keeps structure coarser than 1/cutoff (voxels, or mm with *spacing*).
Finer detail is attenuated smoothly. Transfer exp(-f^2 / (2 cutoff^2)) — the DC level (mean intensity) passes unchanged. Typical use: extract the illumination/thickness drift.
Procedure: real FFT with np.fft.rfftn → multiply by the transfer function exp(-|f|^2 / (2 cutoff^2)) according to each frequency bin's magnitude |f| = sqrt(fz^2 + fy^2 + fx^2) → transform back with irfftn. Returns float64 of the same (D, H, W) as the input (passing spacing does not change the shape).
Arguments:
• cutoff: positive finite value. With spacing=None it is in cycles/voxel (Nyquist = 0.5); passing spacing=(sz, sy, sx) (mm, or a volio.VolumeMeta with spacing_mm) makes it cycles/mm. For anisotropic voxels each axis is converted to physical frequency with fftfreq(n, d=spacing), so the same physical structure is treated the same way.
• The attenuation is Gaussian: at |f| = cutoff it is exp(-1/2) ≈ 0.61 (not a brick-wall filter. No ringing appears).
Validation (ValueError): not 3-D / NaN or Inf / voxel count over MAX_VOXELS (1 << 27) / cutoff non-positive, non-finite, or so small that its 2nd power underflows / spacing not of length 3 or non-positive.
Note: the FFT treats the volume as periodic. If opposite faces differ strongly in luminance, it leaks across the wrap (no windowing is applied silently). vol_fft_highpass is exactly this complement 1 - lowpass, and the sum of the two equals the input.
• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).
• Operator provenance and references — the sources of the research/methods this op family came from.
• deconv_fft_restore — py -3.11 examples_3d/deconv_fft_restore.py
voxel as input)voxel_to_mips · voxel_to_mesh · signed_distance_field · to_points · sobel3d · hessian3d · curvature_maps · edt_jfa
frequency)vol_fft_highpass · vol_fft_bandpass
*Provenance: volfreq.py — 3D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.