region op• Data kinds: region → region
• Call: fullseye.apply(img, "r3_rank_region", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: rank_region (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).*
Morphological rank operator on a region (HALCON's genuine `rank_region`: a generalisation that is neither pure erosion nor pure dilation).
> The detailed description below is the original text — the summary and the headings are translated.
`sz x sz(sz は 3, 5, 7 のいずれかを a で選ぶ)の窓の中で、領域に属する画素が number 個以上あれば出力を立てる。number はb(0〜1)を窓面積に対する割合として決める(number = sz*sz で収縮相当、number = 1` で膨張相当、中間ではランク/メディアンフィルタ相当の挙動になる)。
• gallery2d_region 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 r3_rank_region 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_region — py -3.11 examples/gallery2d_region.py
region as input)identity · reg_erode · reg_dilate · reg_open · reg_close · fill_holes · select_largest · remove_small
region)reg_erode · reg_dilate · reg_open · reg_close · fill_holes · select_largest · remove_small · invert_region
*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.