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.
Create: Strokes drew every line with round caps: a square-ended line 10 px wide
had its corners 2.94 px outside the stroke.
- A line's ends are square when its ink reaches as far a third of the width to
either side of its middle as along it (a round end stops short there by a
seventh of the width); told from lines 3 px wide and more, all the ends of a
line together. The stroke then has square caps (`TracedPath::square_caps`).
- The last points of a wide line's skeleton can turn towards a corner of its
end. An end that has left the line the skeleton followed a width back (by a
quarter of the width, 1 px at least) is put back on it; and an end may be
pulled back as well as pushed out to where the ink ends.
Outline on the thin-line inputs: largest distance from the art 2.94 -> 0.88 px
(clean 2.94 -> 0.41; aliased 0.88 -> 0.81), mean 0.055 -> 0.050 px, anchors
14 -> 10.
Gradients (params `gradients`, a checkbox in the panel for Grayscale and Color;
off unless asked for): an area whose colour changes evenly along one direction
is traced as one path filled with a linear gradient, not as bands of flat colour.
Gradients are found before the palette is made, so no colour is spent on their
bands: a connected run of smoothly changing pixels is a gradient when a plane
fits each colour channel with all three sloping the same way, the colours along
that way are at most six stops with ramps between them, and painting them back
gives the area's own pixels. Flat colour, soft edges between flat colours and
shading that goes two ways are left as they were.
The harness gains two linear-gradient inputs with known lines and stops, and
measures whether each is found, the angle of its line and the colours of its ramp.
Auto Grouping (params `autoGrouping`, a checkbox in the panel; off unless asked
for): each traced path that has others inside its outer contour comes out in a
group with them, the path first, nested as deep as the picture is. The path that
covers the whole image is nobody's group.
The grouped result paints the same picture: where paths can overlap (stacked
layers, Flat Logo, strokes) a path only joins a path below it, and only if that
moves it under nothing that shares any of its box.
The harness measures three presets with the option on ("grouped %"), painting
them in the grouped order.
bflatastic