Restroke — SVG fills to centerlines

Accuracy and smoothing

Bézier fitting error --error

auto SVG units

Maximum deviation of the output curve from the centerline that was found. Lower — follows the shape more closely, but adds nodes and file weight. Higher — smoother and lighter, small wiggles get cut off. The same value doubles as the dust threshold: lines shorter than it are dropped. Auto = drawing size / 150.

Contour sampling step --step

auto SVG units

How densely the outline is turned into points before the Voronoi diagram is built — in other words, how finely the centerline itself is searched for. Lower — a more accurate and stable axis, but the running time grows fast. Higher — quicker, but the axis starts to wobble and break up. Auto = 1/8 of the shape's own stroke thickness, which is why it behaves the same on a 24×24 icon and on a 10000×10000 artboard.

Flattening resolution --flatten

auto SVG units

How finely the source Bézier curves are split into segments while the file is parsed. This is the real accuracy ceiling of the whole pipeline: setting the fitting error finer than the flattening makes no sense — the result cannot be more precise than its input. Auto = drawing size / 800.

Bézier arm cap --arm-cap

× chord

How long the curve's control handles may get, as a fraction of its own chord. On nearly straight runs the least-squares fit degenerates and can throw a control point far off to the side: you get a loop or a tail at a formally tiny error. 1.0 — safe; higher — freer curves and a higher risk of loops.

Skeleton topology

Spur pruning strength --prune

× half-thickness

Threshold for removing parasitic twigs of the skeleton, in multiples of the local half-thickness. A flat end always forks into two whiskers running to the corners, r·√2 ≈ 1.41r long, so below about 1.5 the corners keep their forks. Higher — cleaner lines, but short genuine branches (serifs, short tails) get eaten.

Extend open ends --no-extend

The centerline physically stops short of the end cap by r — that is the last point where the inscribed circle still touches both sides. Without extension every stroke is half a thickness short at each end and the joints sit with gaps. Extension pulls the end either to the shape's boundary or to the centerline of the neighbouring stroke, which gives a clean T-joint.

Dot threshold (kept as fill) --blob

length / width

A dot, a disc or a small square has no centerline to speak of, so shapes like these are copied into the result as they are — as fills. A compact shape counts as a dot when the aspect ratio of its minimum bounding rectangle is below this value. Higher — more shapes stay filled; lower — they turn into short strokes.

Pass through stroked paths --no-strokes

Paths with fill="none" and a stroke are already centerlines — they are carried into the result with their original geometry and width. Turn this off if you do not need those paths from the source.

Output styling

Stroke width --width

auto — every path gets the thickness of its source stroke (2r, measured on the shape). median — a single median thickness across the drawing, handy for uniform icon sets. thin — 15% of the median, useful for inspecting the line geometry itself. number — a fixed thickness in SVG units.

Force colour --color

When off, the colours of the source fills are preserved (shapes are grouped by colour and processed separately). When on, every output path gets this one colour; any SVG colour value is accepted, including currentColor.

Source—

Result—

Load an SVG and hit Convert

Ready