post op• Data kinds: image2d → image2d
• Call: import fullseye as fs; fs.ledger.dither(img, levels=2, method='ordered', matrix_size=4) (to call the implementation directly, import gfx2d; gfx2d.dither(img, levels=2, method='ordered', matrix_size=4); from the registry, 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).
• 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.
• gfx2d_scene — py -3.11 examples/gfx2d_scene.py
image2d as input)shadow_cast_2d · raw_black_level · raw_dead_pixel_mask · raw_dead_pixel_correct · lens_shading_gain · lens_shading_correct · raw_apply_gains · raw_demosaic_bilinear
post)bloom · vignette · chromatic_aberration · film_grain · color_lut · color_grade · palette_quantize
*Provenance: gfx2d.py — GFX2D 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.