region op• Data kinds: region → region
• Call: fullseye.apply(img, "r2_smallest_rectangle1", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
*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):
▸ r2_smallest_rectangle1: stages (docs site)
On other images (synthetic scene / photo / coins. Top row: inputs, bottom row: their outputs. Knobs at default):
▸ r2_smallest_rectangle1: other inputs (docs site)
Axis-aligned bounding box (smallest_rectangle1).
Draws the region's circumscribed axis-parallel rectangle (bounding box) as a mask. For the foreground pixels of the foreground mask (> 0.5) it takes the row/column minimum/maximum ys.min()..ys.max(), xs.min()..xs.max() and paints that range with 1.0. a, b are unused.
The return value is a float64 0/1 mask of the same shape as the input. All zeros if there is no foreground. The output always contains the input region. If there are several connected components, the result is 1 rectangle enclosing all components together (if you want a bbox per component, first narrow down with r2_sort_region or select_largest to 1 component). The coordinates of the rectangle's 4 corners themselves are not returned (mask representation). A single isolated noise pixel (1 pixel) is enough to enlarge the rectangle greatly, so apply remove_small or opening_circle upstream. The minimum-area rectangle allowing rotation is r2_smallest_rectangle2; the inscribed counterpart is r2_inner_rectangle1.
• 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 r2_smallest_rectangle1 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.