Centreline tracing for line art in Vectornation by Zaweba

Most tracing turns an image into filled shapes. For a pen drawing that is often the wrong answer. A line drawn with a fineliner is one line, and you want it back as one stroked path, not as a thin filled outline with an edge on each side. Centreline tracing in Vectornation by Zaweba gives you exactly that.

It takes line art and finds the middle of each drawn line. The result is a set of stroked lines, joined through the places where lines meet, with the short spurs that scanning tends to leave behind removed.

Outlines versus centrelines

It helps to picture the difference. An ordinary trace of a line two pixels wide gives you a long, thin filled shape. Change its stroke and nothing useful happens, because it has no stroke, only a fill. Scale it up and the line thickens with it. Try to cut it on a machine and the cutter follows both edges.

A centreline trace gives you a path running down the middle with a stroke on it. You can set the stroke weight to anything, swap in a brush, add width variation, or hand it to a pen plotter that will draw it once. For technical drawings, maps, signatures, hand lettering in a single weight, embroidery outlines and plotter art, that is what you need.

Junctions and spurs

Real drawings cross and branch. Where three lines meet in a T or four meet in a cross, a naive centreline trace tends to break up into fragments that stop just short of each other. Centreline tracing here joins lines through junctions so that a crossing reads as continuous strokes.

Spurs are the other common nuisance. Scanned ink often has small bumps along a line, and where two lines meet at a shallow angle the tracer can see a short extra branch. These spurs get removed, so you are not left deleting dozens of tiny stubs.

Getting good line art to trace

The cleaner the source, the better the result. A good scan or photo of the drawing, with even lighting and strong contrast between line and paper, matters more than any setting. If the paper is grey or the lines are faint, use the levels controls in the Image Trace panel to push the paper to white and the ink to black before you trace.

Lines that are roughly even in width trace most predictably. Centreline tracing finds the middle of a line, so a drawing with heavy filled areas, such as solid black shadows, is not really line art. For those, a normal trace, or a mix of the two on separate copies, is the better route.

After the trace

Once you have strokes, the rest of Vectornation by Zaweba treats them like any other path. Set a stroke weight that matches the original, or try a heavier one for a bolder look. Apply a brush for a hand-drawn feel. Use the direct selection tools to fix the odd join that came out wrong.

If the work is going to a cutter or plotter, G-code export takes stroked paths to laser cutters, pen plotters and drag knives, which makes centreline tracing a natural first step for turning a sketch into something a machine can draw.

Things that catch people out

Tracing a coloured illustration with centreline tracing rarely gives a useful result. It is designed for line art, so keep it for drawings where the line is the picture.

Small text in a scanned drawing is another weak point. Letters are short strokes packed close together and can merge into one another. If a drawing has a title or labels, consider tracing the drawing and setting the text again as live type.

And keep the original image. The placed picture is still there after tracing, so if a junction or a curve needs another attempt with different settings, you can trace it again rather than redrawing.