features op• Data kinds: region → match
• Call: fullseye.apply(img, "area_center", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: area_center (the HALCON reference is a useful guide to its meaning and parameters)
Returns the area and centroid of a region as a resolution-independent normalized 3-component vector (area ratio = area / number of image pixels, normalized centroid row, normalized centroid column). Since a single scalar cannot represent (Area, Row, Column), it differs from other region-feature ops by returning a `match-sort value (a 1-D vector, the same shape as ncc_locate). It has a fail-soft specification: when the region is empty it returns (0, 0.5, 0.5) -- zero area, center = image center. Equivalent to HALCON's area_center` (Area and center of regions.).
> 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
match 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.