Each documented preset has an enhanced version (`enhanced: true` in
`imageTrace.make`, an Enhanced checkbox under the panel's preset): the preset
with Auto Grouping, and with Shapes in all but High Fidelity Photo. Gradients
stay an option. Flat Logo, a preset of our own, has none. The legacy presets,
and documents traced with them, are as they were.
So that an enhanced preset is no worse than its preset on that preset's inputs:
- A hole that one colour fills is the same shape as the path that fills it, so
the two still share one outline (a shape beside a fitted hole left slivers).
- A rectangle is as large as where its sides lie on average, not their farthest
points.
- Auto Grouping keeps the paths of a group in the order they were traced in. It
put a path first and what is inside it on top: a white counter traced under
its black letter was then painted over the letter's edge, a light seam
(Default with Auto Grouping, edge dE 10.24 -> 9.88; legacy 10.05).
The harness measures every enhanced preset beside its preset.
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