halcon_ext op• Data kinds: contour → feature
• Call: fullseye.apply(img, "hx_fit_ellipse_contour", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: fit_ellipse_contour_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):
▸ hx_fit_ellipse_contour: stages (docs site)
Fit an ellipse from the second moments and return the axis ratio (minor/major: 1 for a circle, toward 0 the more elongated).
Pools the points of all contours, takes the eigenvalues λmin, λmax of the coordinate covariance matrix, and returns sqrt(λmin/λmax) (the ratio of the standard deviations along the principal axes = minor/major axis of the inertia ellipse) as np.float64.
• a, b are unused.
• 0.0 if there are fewer than 3 points or λmax <= 1e-9 (all points coincide). Negative eigenvalues are clipped to 0.
Close to 1 means isotropic (a true circle); close to 0 means elongated. This is the 2nd-order moment of the point set, not an algebraic fit of an ellipse boundary, so the axis ratio changes with uneven point density or missing arcs. The ellipse's tilt and centre are not returned (orientation_xld / area_center_xld). The cv2.fitEllipse version is elliptic_axis_xld. Deviation from an ellipse is hx_dist_ellipse_contour.
• gallery2d_halcon_ext 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 hx_fit_ellipse_contour 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_halcon_ext — py -3.11 examples/gallery2d_halcon_ext.py
feature as input)halcon_ext)hx_gen_circle · hx_gen_ellipse · hx_gen_rectangle2 · hx_gen_checker_region · hx_gen_grid_region · hx_gabor · hx_fit_surface1 · hx_fit_surface2
*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.