halcon_ext op• Data kinds: image → region
• Call: fullseye.apply(img, "hx_char_threshold", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: char_threshold (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):
▸ hx_char_threshold: knob a sweep (docs site)
*Knob b does not change the output (measured: identical at 0.1 / 0.5 / 0.9).*
On other images (synthetic scene / photo / coins. Top row: inputs, bottom row: their outputs. Knobs at default):
▸ hx_char_threshold: other inputs (docs site)
*The 4th column is a colour (H,W,3) input. This op handles colour without crossing channels (it does not convolve the colour channel as a third spatial axis).*
Extract dark characters from a bright background (region): pick the lower side at thresh = mean − k*std (k from a).
> The detailed description below is the original text — the summary and the headings are translated.
画像全体の平均 `mean と標準偏差 std から thr = mean - k*std を計算し、v < thr` の画素を 1 とする
0/1 の float region を返す。暗い文字が少数派で明るい背景が多数派、という前提の大域しきい値。
• `a → 係数 k = 0.2 + 1.8*a`(0.2〜2.0)。大きいほど厳しく(より暗い画素だけ)、小さいほど多く拾う。
• `b` は未使用。
濃淡が一様な画像では `std = 0 となり thr = mean` で「平均未満」だけが残る。照明ムラがあると 1 本の
しきい値では片側が欠けるので、前に `hx_plane_deviation で背景を引くか、局所版の dyn_threshold` /
`local_threshold` を使う。明るい文字を取りたい場合は先に画像を反転する(この op は下側しか選ばない)。
• gallery2d_halcon_ext 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.
hx_char_threshold 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_halcon_ext — py -3.11 examples/gallery2d_halcon_ext.py
region as input)identity · reg_erode · reg_dilate · reg_open · reg_close · fill_holes · select_largest · remove_small
halcon_ext)hx_gen_circle · hx_gen_ellipse · hx_gen_rectangle2 · hx_gen_checker_region · hx_gen_grid_region · hx_gabor · hx_fit_surface1 · hx_fit_surface2
*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.