segmentation op• Data kinds: image → region
• Call: fullseye.apply(img, "hysteresis_threshold", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: hysteresis_threshold (the HALCON reference is a useful guide to its meaning and parameters)

*The figure is the real output on a synthetic 128×128 input. Left: input, right: output (a non-image return value is shown as the value itself).*
Hysteresis thresholding (`skimage.filters.apply_hysteresis_threshold). Among pixels exceeding a low threshold (0.2+0.3*a), only those connected to pixels exceeding a high threshold (0.5+0.3*b) are kept as foreground -- an edge-extraction technique resistant to gaps, also used as post-processing for Canny edge detection. Corresponds to HALCON's hysteresis_threshold` (Perform a hysteresis threshold operation on an image).
> The detailed description below is the original text — the summary and the headings are translated.
`a が低いしきい値を、b` が高いしきい値を振る。両方が使われる。
• gallery2d_segmentation 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.
hysteresis_threshold 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_segmentation — py -3.11 examples/gallery2d_segmentation.py
region as input)identity · reg_erode · reg_dilate · reg_open · reg_close · fill_holes · select_largest · remove_small
segmentation)threshold · otsu · canny · adaptive_gauss_thresh · sk_otsu · sk_li · sk_yen · sk_sauvola
*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.