A fourth Image Trace mode for flat-colour logos. The existing tracer follows hard pixel
edges, so an outline can only be as good as the pixel grid; here each pixel is read as a
blend of the logo's flat colours, the blend is interpolated smoothly (cubic B-spline), and
every outline is placed where two colours are equally present, to a fraction of a pixel.
Outlines are then cleaned the way a person would:
- corners the blur rounded are put back (line fits either side of a bend, intersected);
- near-straight runs and near-circular arcs become exact lines and arcs (Snap Curves To Lines);
- the rest is fitted with as few cubic Beziers as the tolerance allows (Schneider);
- touching colours overlap by 0.06 px so no hairline gap opens between independent fits;
- shapes are painted biggest first; transparent areas fully enclosed by artwork (letters
knocked out of a badge, the counters of an "o") are painted white so the logo reads the
same on any background, or become real holes with Ignore White (each hole belongs to the
smallest outline containing it);
- an outline whose fit strays more than 1.4 px from the raw contour is fitted plainly.
Colours are found automatically (and completed from pixels no blend of the known colours
explains, so a small accent is not lost) or named with `logoColors: ["#rrggbb", ...]` (white is
always its own class; colours closer than 12 count as one; at most ten). Gradients and photos
are refused with advice to use Color (a flat-colour score of the solid areas, 0.93). A
hard-edged source with no anti-aliasing is softened by under a pixel and fitted with looser
snap tolerances. Images over 1024 px on the long side are averaged down first (further, if
they are busy enough to make the unmixing expensive) and the result is mapped back exactly.
More real outlines than we will fit are refused, not silently truncated.
Also: a "Flat Logo" preset, the mode in the Image Trace panel (Method hidden: it always
stacks), the command docs and MCP prompt, es/fr/it/ru translations for the two new messages
and the mode name, and the ROADMAP.
Never-crash: no unwrap/expect/panic, every size and float is bounded and checked, with
tests for degenerate and extreme input (NaN/infinite parameters, 0x0 and 1x1 images, sparse
outlines, an anchor budget, a 200,000-entry palette) and a 250-run randomised no-panic
property test. The B-spline interpolation follows Unser et al. and Thevenaz et al., and the
curve fitter follows Schneider (Graphics Gems); both are written from the papers.
Measured (local experiment, not in CI): a flat-colour logo's vector original rendered down
to a soft 199x100 px PNG and traced. Mean edge error vs the original at 1600 px wide:
built-in colour presets 2.5 to 3.4 px, Flat Logo 0.78 px (0.48 px from a crisp source);
region overlap 0.88-0.91 vs 0.966. About 0.1 s for a 200 px logo.
Tests: 60 new in the trace crate (unmix, field, contours, geometry, Beziers, corners,
outline fitting, palette, end-to-end on synthetic shapes made in code) and 3 in the engine.
cargo xtask ci passes (fmt, clippy, test, assets, brands, layers, wasm): 4,290 tests.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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