features op• Data kinds: region → match
• Call: fullseye.apply(img, "eccentricity", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: eccentricity (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):
▸ eccentricity: stages (docs site)
Returns the three ellipse-derived shape features (Anisometry, Bulkiness, StructureFactor) as a 3-component vector of match sort (a single scalar cannot carry three values — the same shape as area_center).
With Ra/Rb the radii of the ellipse with the same moments and A the area:
Anisometry = Ra/Rb (elongation; 1 for a circle, lower bound 1)
Bulkiness = π·Ra·Rb / A (how much of the ellipse is left unfilled; 1 for a circle)
StructureFactor = Anisometry·Bulkiness - 1 (0 for a circle)
Same as HALCON's eccentricity (Shape features derived from the ellipse
parameters.): the same 3 values, the same formulas. All 3 are dimensionless, so they are not normalised.
★Until 2026-09-26 it returned skimage's eccentricity sqrt(1-(b/a)²), a quantity that is none of the 3, as 1 scalar (0.0 vs HALCON's 1.0 for a circle, 0.999 vs 20.65 for a 4x80 bar). Since 1 scalar cannot represent 3 values, it was changed to the same match sort as area_center. docs/hardening/halcon-named-shape-factors.md.
When the region is empty it returns the circle's values (1, 1, 0) as fail-soft behaviour (the number of components does not change with the input). 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 eccentricity 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_features — py -3.11 examples/gallery2d_features.py
• poc_rotation_invariance_audit — py -3.11 examples/poc_rotation_invariance_audit.py
match 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.