var_threshold — 2D `segmentation` op

• Data kinds: image → region

• Call: fullseye.apply(img, "var_threshold", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])

• HALCON equivalent: var_threshold (the HALCON reference is a useful guide to its meaning and parameters)

var_threshold: 入力 → 出力

*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).*

Usage

Sauvola's local adaptive binarization (`skimage.filters.threshold_sauvola, window size 2*int(a*6)+3). Since the threshold is determined using both the local mean and local standard deviation, it is more robust to uneven illumination and low-contrast documents than dyn_threshold. An approximation corresponding to HALCON's var_threshold` (Threshold an image by local mean and standard deviation analysis) -- the formulation follows a similar idea, but Sauvola's formula and HALCON's formula have different coefficients, so the numerical results are not identical.

> The detailed description below is the original text — the summary and the headings are translated.

`a が局所窓のサイズを振る。b` は未使用(Sauvola の k, r は skimage の

既定値に固定)。

Detailed usage guide

• gallery2d_segmentation family guide

References (sample data, literature)

• 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.

Try it in Studio

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.

var_threshold 0.50 0.50

▸ Load this pipeline · Load & run

Runnable examples (verified samples that actually call this op)

• gallery2d_segmentation — py -3.11 examples/gallery2d_segmentation.py

• poc_document_scan — py -3.11 examples/poc_document_scan.py

Ops the type connects to (they accept `region` as input)

identity · reg_erode · reg_dilate · reg_open · reg_close · fill_holes · select_largest · remove_small

Same category (`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).*

var_threshold — 2D segmentation op