halcon_ext op• Data kinds: image → image
• Call: fullseye.apply(img, "hx_nonmax_dir", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: nonmax_suppression_dir (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_nonmax_dir: 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_nonmax_dir: 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).*
Non-maximum suppression along the gradient direction (Canny's NMS stage). Thins edges to one pixel.
> The detailed description below is the original text — the summary and the headings are translated.
Sobel で `gx(列方向)・gy(行方向)を取り、振幅 hypot(gx, gy) と方向 arctan2(gy, gx) mod 180°` を
求める。方向を 45° 刻みの 4 区分に量子化し、各画素をその区分に対応する 2 つの隣接画素と比べて
`mag >= 両隣 の画素だけ残す(それ以外は 0)。残った振幅を min-max で [0,1] に正規化し、a*0.3` 未満を 0 に落とす。
• `a → 弱エッジのしきい値 a*0.3`(正規化後の値に対して。a=0 でしきい値なし)。
• `b` は未使用。
注意点:
• 隣接比較は `np.roll` なので画像端では反対側の画素と比較される(端 1 画素は信用しない)。
• 比較が `>=` のため、同じ振幅が並ぶ理想的なステップエッジは 2 画素幅で残る(1 画素にはならない)。
• 現状の実装では 45° と 135° の区分で比較する隣接画素の対が入れ替わっており、斜めのエッジは勾配方向でなく
エッジに沿った方向で比較される。そのため水平・垂直エッジは細線化されるが、斜めエッジはほとんど細線化されない
(ぼかした対角ステップエッジで 1400 画素前後がそのまま残る実測)。斜めエッジの細線化が要る場合は `canny` や
`skeleton` を検討する。
`sobel_amp のような振幅画像ではなく元の gray 画像を渡す(内部で微分する)。後段は hx_close_edges` /
`hx_detect_edge_segments / threshold`。
Value comparability (measured): the output is normalised by that image's own maximum (the output maximum is always 1.0, and scaling the input leaves the output unchanged). Values therefore cannot be compared across images — a feature of the same strength takes a different value depending on what the strongest feature in that image happens to be, and in an image holding only weak features the noise is lifted to 1.0. To compare across images, rescale by a common reference.
Blank frame (measured): feeding an image of uniform brightness gives an empty result — every pixel is background (0) — regardless of the brightness. Pure white and pure black behave alike; brightness by itself detects nothing.
• 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_nonmax_dir 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_halcon_ext — py -3.11 examples/gallery2d_halcon_ext.py
image as input)identity · gaussian · mean_box · bilateral · unsharp · median · min_filter · max_filter
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.