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.).
★Until 2026-09-26 it applied /10 and cut off with min(1.0, ...) -- a convenience to keep the value within [0,1], but every shape whose perimeter²/(4π·area) exceeds 10 (with a width of 2 px, a scratch of length 80 or more) was crushed all to 1.0. So in scratches and cracks, the regions one most wants to see, "different shapes, same number" was being returned. The range [0,1] was never part of the feature contract (elliptic_axis returns 6.35, r3_region_features 18.1), so there was no reason to crush it -- docs/hardening/compactness-saturated-at-one.md.
HALCON clips from below with max(1, C) (because the pixel approximation can fall below 1), but here it is not clipped. A value below 1 is itself the information that "the region is too small for the approximation to work", and the caller can clip it if needed.
a, b are unused.
• 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.