fullseye

dither — GFX2D post op

• データ種: image2d → image2d
• 呼び出し: import fullseye as fs; fs.ledger.dither(img, levels=2, method='ordered', matrix_size=4) (実装を直接呼ぶなら import gfx2d; gfx2d.dither(img, levels=2, method='ordered', matrix_size=4)、台帳から引くなら opsgfx2d.get("dither"))

使い方

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).

参考(サンプルデータ・文献)

• 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。

実行できる例(この op を実際に呼ぶ検証済みサンプル)

• gfx2d_scene — py -3.11 examples/gfx2d_scene.py

型が繋がる次の op(image2d を入力に取れる)

shadow_cast_2d

同カテゴリ(post)

bloom · vignette · chromatic_aberration · film_grain · color_lut · color_grade · palette_quantize

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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.

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