halcon_ext op• Data kinds: contour → feature
• Call: fullseye.apply(img, "hx_fit_rectangle2_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_rectangle2_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_rectangle2_contour: stages (docs site)
Fit the minimum-area oriented rectangle and return its aspect ratio (short side / long side; a feature).
Pools the points of all contours, searches 0° to 84° in 6° steps for the rotation angle at which the area of the axis-parallel bounding rectangle is smallest, and returns that rectangle's short side / long side as np.float64 (the same search as hx_smallest_rect2_xld).
• a, b are unused.
• 0.0 if there are fewer than 3 points. Also 0.0 if the long side is below 1e-9 (all points coincide).
The angle is a discrete search over 15 values, so it can deviate by up to 3° from the true minimum-area rectangle (the more elongated the shape, the smaller the effect on the aspect ratio). The rectangle's centre, angle and side lengths are not returned. Close to 1 means square; close to 0 means elongated. The area ratio of the unrotated bounding rectangle is hx_smallest_rect1_xld; the region version (rotating calipers) is r2_smallest_rectangle2.
• 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_rectangle2_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.