features op• Data kinds: region → feature
• Call: fullseye.apply(img, "compactness", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: compactness (the HALCON reference is a useful guide to its meaning and parameters)
*The figure is the actual output on a synthetic 128×128 input. Left: input, right: output. Point clouds are drawn as a top-down scatter (brightness = z), 1-D series as a line plot, volumes as the maximum-intensity projection along z, videos as the middle frame, complex images as magnitude; return values that are not pictures are shown as the values themselves.*
*Knob a does not change the output (measured: identical at 0.1 / 0.5 / 0.9).*
*Knob b does not change the output (measured: identical at 0.1 / 0.5 / 0.9).*
Stages (the ops that come before → this op, left to right):
▸ compactness: stages (docs site)
Compactness `perimeter^2 / (4pi * area). It is 1 for a circle and grows with elongation, roughness and holes, with **no upper bound**. The same quantity as HALCON's compactness` (Shape factor for the compactness of a region.).
> The detailed description below is the original text — the summary and the headings are translated.
★2026-09-26 まで `/10 して min(1.0, ...)` で切っていた —— 値を [0,1] に
収めるための便宜だったが、`周囲長²/(4π・面積)` が 10 を超える形(幅 2 px なら
長さ 80 以上の傷)を全部 1.0 に潰していた。傷や割れという、いちばん見たい
領域で「形が違うのに同じ数」が返っていたことになる。値域 [0,1] はそもそも
feature の契約ではない(`elliptic_axis は 6.35、r3_region_features` は
18.1 を返す)ので、潰す理由が無かった ――
`docs/hardening/compactness-saturated-at-one.md`。
HALCON は `max(1, C)` と下で切る(画素近似で 1 を下回りうるため)が、
ここでは切らない。1 を下回る値は「領域が小さすぎて近似が効いていない」と
いう情報そのもので、必要なら呼ぶ側で切れる。
`a, b` は未使用。
• gallery2d_features family guide
• 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.
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.
threshold 0.50 0.50 compactness 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_features — py -3.11 examples/gallery2d_features.py
• shape_factors_closed_form — py -3.11 examples/shape_factors_closed_form.py
feature as input)features)effective_bit_depth · blob_count · area_frac · count_contours · total_length · vol_count · sk_euler · sk_entropy_feat
*Provenance: ops.py — 2D 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.