region op• Data kinds: region → region
• Call: fullseye.apply(img, "r2_inner_rectangle1", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: inner_rectangle1 (the HALCON reference is a useful guide to its meaning and parameters)
*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.*
Sweeping knob a (0.1 / 0.5 / 0.9, the other knob at its default):
▸ r2_inner_rectangle1: knob a sweep (docs site)
*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_inner_rectangle1: stages (docs site)
On other images (synthetic scene / photo / coins. Top row: inputs, bottom row: their outputs. Knobs at default):
▸ r2_inner_rectangle1: other inputs (docs site)
Largest axis-aligned inscribed rectangle (a shrinks the drawn rect; a=0=exact).
Draws, as a mask, the axis-parallel rectangle of largest area inscribed in the region. For the foreground mask (> 0.5), it accumulates the consecutive foreground height of each column row by row and obtains the exact solution with the histogram method (O(H*W)), which finds the largest rectangle with a monotonic stack. If there are several candidates of the same area, the first one found in scan order is taken.
a is the fraction by which the drawn rectangle is shrunk inward: with f = 0.3*a, the height is trimmed by round(hh*f/2) rows and the width by round(ww*f/2) columns from both sides. a=0 gives the exact largest inscribed rectangle; at a=1 each side shrinks by about 15% (roughly half in area). If shrinking too far collapses a side, it is rounded to the central 1 row / 1 column. b is unused.
The return value is a float64 0/1 mask of the same shape as the input. All zeros if there is no foreground. Because the rectangle aligns with pixel boundaries, the output at a=0 is always contained in the region (unlike r2_inner_circle, it does not stick out). In a region with holes the rectangle avoids the holes, so if you want to ignore holes, put fill_up upstream. Rotated rectangles cannot be handled (axis-parallel only). The circumscribed axis-parallel rectangle is r2_smallest_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_inner_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.