frei_dir — 2D `edges` op

• Data kinds: image → image

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

• HALCON equivalent: frei_dir (the HALCON reference is a useful guide to its meaning and parameters)

frei_dir: 入力 → 出力

*The figure is the real output on a synthetic 128×128 input. Left: input, right: output (a non-image return value is shown as the value itself).*

Usage

An edge-direction (angle) map using Frei-Chen-type kernels. Computes `arctan2(gy, gx) from the convolution responses of the horizontal kernel _FREI[0] (row/vertical-direction gradient) and vertical kernel _FREI[1] (column/horizontal-direction gradient), and maps it to [0,1] using the same convention as sobel_dir/prewitt_dir` (0/1 = -180 degrees, 0.5 = 0 degrees). a and b are unused.

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

HALCON の `frei_dir（Frei-Chen 演算子でエッジの振幅と方向を検出する演算）のうち方向成分に相当する近似。振幅は frei_amp` 側が担当する。

Detailed usage guide

• gallery2d_edges 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.

Try it in Studio

The program below has been verified to run (same input as the figure). In Studio's help this block becomes buttons that load and run it on the spot.

frei_dir 0.40 0.50

▸ Load this pipeline · Load & run

Runnable examples (verified samples that actually call this op)

• gallery2d_edges — py -3.11 examples/gallery2d_edges.py

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

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

Same category (`edges`)

sobel_mag · prewitt_mag · roberts_mag · dog · grad_dir · log · corner_response · sk_scharr

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

frei_dir — 2D edges op