gray op• Data kinds: image → image
• Call: fullseye.apply(img, "sigmoid", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: scale_image_max (the HALCON reference is a useful guide to its meaning and parameters)
S-curve contrast enhancement using a logistic (sigmoid) function. Mapped to HALCON's `scale_image_max (Maximum gray value spreading in the value range 0 to 255.), but the processing differs from scale_image_max`, which stretches the dynamic range to its maximum (this is closer to a different operation than an approximation).
> The detailed description below is the original text — the summary and the headings are translated.
`a が S字の傾き k = 4 + 12a（4〜16）を、b が中心（変曲点）の位置 x0 = 0.2 + 0.6b（0.2〜0.8）を振る（1/(1+exp(-k*(v-x0)))）。x0` 付近の階調差を強調し、両端の階調差は圧縮する。
• gallery2d_gray_arith 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_gray_arith — py -3.11 examples/gallery2d_gray_arith.py
image as input)identity · gaussian · mean_box · bilateral · unsharp · median · min_filter · max_filter
gray)gamma · invert · scale_clip · equalize · clahe · sk_adapthist · sk_enhance_contrast · sk_autolevel
*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.