halcon_ext op• Data kinds: contour → feature
• Call: fullseye.apply(img, "hx_smallest_rect2_xld", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: smallest_rectangle2_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_smallest_rect2_xld: stages (docs site)
The area ratio of the minimum-area oriented rectangle (rectangle area / image area; a feature).
Pools the points of all contours, rotates them from 0° to 84° in 6° steps, computes the area of the axis-parallel bounding rectangle, and returns its minimum divided by the image area H*W and capped at 1 as np.float64.
• a, b are unused.
• 0.0 if there are fewer than 3 points. 1e-9 is added to each side, so even for collinear points the area is not exactly 0 but a tiny value.
Because the angle search uses 6° steps, the result can come out up to a few % larger than the true minimum area. All contours are enclosed in 1 rectangle, so several separated contours include the empty space between them. The aspect ratio is hx_fit_rectangle2_contour; the axis-parallel version is hx_smallest_rect1_xld.
• 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_smallest_rect2_xld 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.