contour op• Data kinds: contour → contour
• Call: fullseye.apply(img, "fit_line_contours", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: fit_line_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):
▸ fit_line_contours: stages (docs site)
On other images (synthetic scene / photo / coins. Top row: inputs, bottom row: their outputs. Knobs at default):
▸ fit_line_contours: other inputs (docs site)
Approximates each XLD contour with a single straight line. Equivalent to HALCON's fit_line_contour_xld (Approximate XLD contours by line segments.).
a, b are unused. It takes as the line direction the first principal component direction obtained by SVD (singular value decomposition), passing through the centroid of the contour points (the line minimising the sum of squared distances to all points), and replaces the contour with a sequence of points re-placed at equal intervals over the projected extent of the original points. The difference is that the HALCON version can split into a polyline (multiple segments), whereas this implementation turns the whole contour into 1 straight line. Contours with fewer than 2 points are returned as they are.
• gallery2d_contour_measure 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 fit_line_contours 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_contour_measure — py -3.11 examples/gallery2d_contour_measure.py
• poc_screw_thread_metrology — py -3.11 examples/poc_screw_thread_metrology.py
contour as input)identity · select_contours · smooth_contours · contours_to_region · count_contours · total_length · select_contours_xld · smooth_contours_xld
contour)select_contours · smooth_contours · contours_to_region · sk_find_contours · edges_sub_pix · lines_gauss · select_contours_xld · smooth_contours_xld
*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.