Each crack between an inside and an outside pixel is moved to where the pixels across it say the edge is (the
blend of the two tones in the column of pixels across the crack; a thin line by the centroid and sum of its
tone; hard-edged images are read as staircases), and the outline is fitted as Flat Logo mode fits its own:
corners put back, straight runs as lines, a round outline as a circle, the rest as few curves as Paths allows.
Snap Curves To Lines straightens slightly curved runs and makes arcs. A fit that strays from its outline
gives way to a plainer one, and at last to the outline's own points.
On each preset's own inputs, all sizes and variants (docs/image-trace-quality.md):
- Default: outlines 0.313 -> 0.091 px off on average, largest 1.51 -> 1.02; edge error 17.2 -> 10.1;
gaps between abutting paths 63.5 -> 22.2 px, overlaps 67.0 -> 22.4 px
- Black and White Logo: 0.270 -> 0.064 px off, kinks 15.3 -> 0.3, anchors 3.78 -> 2.73 times the art's
- Technical Drawing: 0.201 -> 0.086 px off; Line Art: 0.158 -> 0.093
- Worse: anchors on blurred and scanned thin lines (Line Art 25 -> 77 on average), High Fidelity Photo
(colour error 2.30 -> 2.50, anchors 46,866 -> 81,597, 1 megapixel photo-like image 0.37 -> 1.98 s)
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