lowpass — 2D `frequency` op

• Data kinds: image → image

• Call: fullseye.apply(img, "lowpass", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])

Usage

Low-pass filter via FFT (blurring). No corresponding single HALCON op has been specified.

> The detailed description below is the original text — the summary and the headings are translated.

`a が遮断周波数 cutoff = 0.05 + 0.4a（正規化周波数、0〜0.5 がナイキストまでの範囲）を振る。b は未使用。2-D FFT で rad <= cutoff の低周波成分だけを残し、逆 FFT の実部を [0,1] に clip する。a が小さいほど強くぼける。境界は周期的（FFT の性質上、画像端は反対側と隣接するとみなされる）に扱われ、ndimage 系フィルタの reflect/edge` とは境界処理が異なる点に注意。

Detailed usage guide

• gallery2d_texture_freq family guide

References (sample data, literature)

• 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.

• The canonical algorithm (author, year) and its uses are named in the family usage guide above.

Runnable examples (verified samples that actually call this op)

• gallery2d_texture_freq — py -3.11 examples/gallery2d_texture_freq.py

• signal_filter — py -3.11 examples/signal_filter.py

Ops the type connects to (they accept `image` as input)

identity · gaussian · mean_box · bilateral · unsharp · median · min_filter · max_filter

Same category (`frequency`)

highpass · sk_butterworth · fft_image · power_real · power_byte · phase_rad · highpass_image · bandpass_image

*Provenance: ops.py — 2D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*

lowpass — 2D frequency op