How to trace a line drawing into strokes, not shapes

Centreline tracing is the answer when you want a line drawing back as strokes rather than filled shapes. In Vectornation by Zaweba, choose the centreline option in Image Trace and each drawn line becomes a single stroked path running down its middle, with lines joined where they meet and stray spurs removed. You can then change the stroke weight, colour or brush as with any path.

Ordinary tracing draws round the outside of each mark, so a pencil line becomes a long thin filled shape with an edge on both sides. That looks right on screen but is awkward to edit, and it is no use to a pen plotter or engraver that needs to follow a line once.

When centreline tracing is the right choice

Use it for line art: sketches, technical drawings, maps, handwriting and signatures, outline illustrations, embroidery and engraving designs. Anywhere the meaning is in the line rather than in a filled area, centreline gives you paths that behave the way you expect. Change the stroke from 1 point to 3 points and every line thickens evenly. Swap the colour and the whole drawing changes.

It is also the better choice for machines. A pen plotter draws a stroke; it would draw the outline of a filled shape twice. Vectornation exports G-code for pen plotters, laser cutters and drag knives, so a centreline trace can go straight from scan to machine.

Use the normal fill tracing for logos, lettering with real weight, and anything where solid areas of colour matter.

Tracing step by step

Place the scan or photo of the drawing in your document with File > Place, and select it. Open Image Trace from the Object menu or Window > Image Trace. With the image selected, the result shows live and updates as you change settings, so you can see the effect of each choice.

Set the mode to black and white, since line art is almost always one colour, and choose the centreline option. Use the views to judge the result. Result over image is the most useful here, because you can see whether each traced line sits down the middle of the drawn one. Side by side and split views help too.

When you are happy, Trace makes a live trace, still tied to its settings. Expand turns it into ordinary paths you can edit point by point.

Getting a clean result

Start with a good scan. Dark, even lines on a clean background trace far better than a faint photo with shadows across it. If your drawing has smudges or paper texture, the trace may pick them up as tiny lines, so tidy the picture first or delete the strays afterwards.

Look closely at junctions. Vectornation joins lines through junctions and removes the little spurs that tracing tends to leave where lines cross, but very dense hatching or lines that touch only by accident can still join where you didn't mean them to. Check the busy areas and cut or delete as needed.

After the trace

Expanded strokes are ordinary paths, so the rest of the program opens up. Give them a calligraphic or art brush to bring back a hand drawn feel. Use the Width tool to vary the thickness along a stroke, which turns a uniform trace into something livelier. Path clean up commands in Object > Path, such as simplify and smooth, remove extra points where the trace followed a wobble too faithfully.

A sketch turned into clean strokes is easy to recolour, resize and send to print or a plotter. Vectornation by Zaweba does it on your PC, offline, with the result live until you decide to expand it.