post op• データ種: image2d → image2d
• 呼び出し: import gfx2d; gfx2d.dither(img, levels=2, method='ordered', matrix_size=4) (または opsgfx2d.get("dither"))
Quantise to `levels` values per channel while preserving the local mean.
`method`:
• `"ordered" — Bayer threshold matrix of side matrix_size` (a power of
two, 2..16). The mean error has a closed-form bound: for a uniform
patch the output mean is within `0.5 / (matrix_size**2 * (levels-1))` of
the input, because the fraction of thresholds crossed is the input
fraction rounded to the nearest `1/matrix_size**2`. At the defaults
(4, 2 levels) the bound is 0.03125; the suite checks it holds for 101 grey
levels x 3 matrix sizes, with zero violations.
• `"floyd_steinberg"` — error diffusion with the 7/3/5/1 sixteenths of
Floyd & Steinberg 1976, serial and directional.
Which method preserves the mean better depends on the image, and this
docstring will not pretend otherwise. Measured on a 128-step horizontal
ramp: ordered is exact (0.0) at 2, 3 and 4 levels and drifts to 1.1e-3
at 8 levels, while Floyd-Steinberg is 7.3e-4 at 2 levels and improves to
4.1e-5 at 16. Ordered wins where the level lattice divides the ramp, error
diffusion wins where it does not.
Accepts `(H, W) or (H, W, 3|4)`; an alpha channel is quantised too,
because a dithered sprite with a smooth alpha is exactly the case that
motivates this.
Output values lie on the lattice `k / (levels - 1)`.
• サンプルデータ カタログ(DL URL / ライセンス) — 2-D は skimage.data(BSD/public)+ 合成、3-D は実データ源(Stanford/PDS 等)の DL URL。
• 演算子の来歴・参考文献 — この op 族の元になった研究/手法の出典。
• アルゴリズムの正典(著者・年)と用途は上記ファミリ使い方ガイドに記載。
• gfx2d_scene — py -3.11 examples/gfx2d_scene.py
image2d を入力に取れる)post)bloom · vignette · chromatic_aberration · film_grain · color_lut · color_grade · palette_quantize
*Provenance: gfx2d.py — GFX2D operator registry. この per-op ノートは tools/opdocs.py md が自動生成(手編集しない)。*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.