Inkscape Centerline Trace
Centerline tracing finds the centre axis of each line element and produces a single-stroke path rather than an outline. This is essential for laser engraving, pen plotters, and CNC machines where you want the tool to follow the line's centre.
About Inkscape centerline trace
Standard vectorization (Potrace/Autotrace) traces the edges of shapes, producing outline paths with fill areas. Centerline tracing instead finds the centre axis of each line element and produces a single-stroke path that follows the line's middle. This is essential for laser engraving, pen plotting, and CNC engraving where you want the laser or tool to follow the line centre rather than cut around its edges.
When to use centerline trace: use it for hand-drawn line art, technical pen drawings, circuit board traces, musical scores, line calligraphy, or any artwork where a single-stroke path is more useful than a closed filled outline.
Inkscape's built-in Trace Bitmap does not include a centerline algorithm. The centerline method requires the Centerline Trace extension or a manual workflow.
Method 1 — Inkscape Centerline Trace Extension: install the Inkscape Centerline Trace extension (available from the Inkscape extensions repository). Access via Extensions > Generate from Path > Centerline Trace. The extension analyses the input bitmap and generates single-stroke paths along detected line centres.
Method 2 — Manual workflow: trace the image with Potrace (Brightness Cutoff, low threshold). Select all traced paths. Use Path > Stroke to Path to convert filled outlines to stroke paths. In Path Effects, apply a Thinning or Skeleton effect (available in Inkscape 1.2+).
For laser engraving of line art: centerline output produces cleaner, faster engraving than outline-traced paths because the laser travels the line once rather than twice (once for each edge of the outline).