features op• Data kinds: contour → feature
• Call: fullseye.apply(img, "circularity_xld", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: circularity_xld (the HALCON reference is a useful guide to its meaning and parameters)
For the largest contour, computes the area via the shoelace formula and the perimeter as the sum of segment lengths, then calculates circularity as `4π・area/perimeter² (the contour-based version of the region-based circularity). Corresponds to HALCON's circularity_xld` (Shape factor for the circularity (similarity to a circle) of contours or polygons.).
> The detailed description below is the original text — the summary and the headings are translated.
`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.
• gallery2d_features — py -3.11 examples/gallery2d_features.py
feature as input)features)blob_count · area_frac · count_contours · total_length · vol_count · sk_euler · sk_entropy_feat · sk_blur_effect
*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.