segmentation op• Data kinds: image → region
• Call: fullseye.apply(img, "dual_threshold", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: dual_threshold (the HALCON reference is a useful guide to its meaning and parameters)
A thresholding operation for signed images. Treats the median value 0.5 as "zero" and takes pixels satisfying `|x - 0.5| > 0.1+0.35*a (pixels sufficiently far from 0.5) as foreground — responding symmetrically to both the positive and negative side. Corresponds to HALCON's dual_threshold` (Threshold operator for signed images.) (HALCON can have separate thresholds for positive and negative, but this is simplified to a symmetric band centered on 0.5).
> The detailed description below is the original text — the summary and the headings are translated.
`a が除外帯域の半幅を振る。b は未使用。highpass_image` や
`bandpass_image` のような符号つき応答(0.5=ゼロ)の後段でよく使う。
• 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.
• 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.