features op• Data kinds: contour → match
• Call: fullseye.apply(img, "eccentricity_xld", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: eccentricity_xld (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_xld: stages (docs site)
Contour counterpart of eccentricity. For the largest contour it returns (Anisometry, Bulkiness, StructureFactor) as a 3-component vector of match sort. The same three values and the same formulas as HALCON's eccentricity_xld (Shape features derived from the ellipse parameters of contours or polygons.).
★Ra/Rb are derived from the geometric moments of the enclosed area. Until 2026-09-26 cv2.fitEllipse (a least-squares fit to the contour "points") was used, and for elongated shapes it was far off -- Anisometry 39.1 vs 20.65 for a 4x80 bar. HALCON's definition is the one derived from the moments.
When cv2 is not available, there are too few points, or the area is 0, it returns the circle's values (1, 1, 0). 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 sk_find_contours 0.50 0.50 eccentricity_xld 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_features — py -3.11 examples/gallery2d_features.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.