Vectorizing a scanned drawing without losing the line

Most of the quality is decided here, and it costs nothing.

Use a scanner, not a phone, if you can. A phone photo brings perspective distortion and uneven lighting across the page. A flatbed gives you even illumination and a flat plane.

Scan at 600 DPI or higher. More resolution gives the tracer more information about where a line actually is. For line art this matters more than it does for photographs.

Scan in greyscale, not colour. Colour scanning of a pencil drawing captures paper tint and introduces variation that has nothing to do with your drawing.

If you must use a phone: shoot in bright even light with no shadow across the page, hold the camera parallel to the paper, and crop tight afterwards.

Three adjustments, in this order, each of which does more for the result than any tracer setting.

Levels. This is the big one. Pull the white point down until the paper goes pure white and the texture disappears. Pull the black point up until your lines are solid. What you're aiming for is a drawing on genuinely white paper, not grey-on-cream.

Go carefully: push the white point too far and light pencil strokes vanish entirely.

Contrast. After levels, add contrast to firm up the edges of each stroke.

Despeckle. Pencil scans pick up isolated dark pixels from paper grain and dust. These trace as hundreds of tiny blobs. Most editors have a despeckle or dust-and-scratches filter; a light pass removes them without eating your line work.

Ink is the easiest. Solid, consistent, high contrast. Clean the scan and trace.

Marker is nearly as good, though broad markers can have uneven coverage that traces as a hollow outline instead of a filled stroke. Raise the levels until the stroke is solid.

Pencil is the hard case. Graphite is grey, not black, and pressure varies along every stroke, so a single line can be dark at the start and nearly invisible at the end. Expect to spend most of your time in levels, and expect some strokes to need redrawing.

Coloured pencil combines both problems: low contrast and colour variation. Consider converting to greyscale first and treating it as a pencil drawing.

For line art, use a monochrome preset — Logo / Line art or Sketch — rather than a colour trace. A pencil drawing has one colour, and asking a tracer to find several produces artefacts.

Check three things in the result:

Broken strokes. Where the pencil lifted, the trace will too. Either go back and strengthen that part in the raster, or join the paths afterwards.

Doubled outlines. Tracing a thick stroke can give you two paths, the outer and inner edge of the stroke, rather than one line. Whether you want that depends on what you're doing with the file.

Background speckle. If you skipped despeckling, you'll see it now as hundreds of tiny paths. Faster to go back and despeckle than to delete them individually.

Tracing a scan works well for line drawings, logo sketches, lettering, signatures, and simple illustration. The result is faithful to the stroke and keeps the character of the hand drawing.

It works poorly for shaded drawings, cross-hatching, and anything where tone matters. Those are better served by posterising deliberately, or by using the scan as a template and redrawing.

If the end goal is a laser or a cutter, there's a separate set of checks before the file reaches the machine.

Tracer is free for SVG, which is enough to see whether a scan cleaned up well before you go further.