Image to DXF

Turning a picture into CAD geometry: what is really happening

It is worth being clear about what this does, because the expectation gap causes most disappointment. A photo or a scan is a grid of coloured dots. A DXF is a list of mathematical shapes — lines, arcs and curves with coordinates. Vectorizing means tracing the boundary between black and white and writing those boundaries out as outlines. It does not recognise what your image depicts, it does not know a circle from a coincidence, and it cannot recover information the picture never contained. What it does extremely well is convert a clean two-tone shape into geometry a machine can follow, which is exactly what you need for a logo, a stamp, a stencil or a traced sketch.

The threshold slider is the whole job

Everything is decided before conversion, by the black-and-white preview. The threshold sets where the tool draws the line between what counts as material and what counts as background, and the preview shows you precisely what will be traced — what you see there is what you get. Spend your time here rather than on the result. A scan with uneven lighting is the classic hard case: one threshold catches the drawing on the bright side of the page and floods the darker corner, and no single setting fixes both. Improving the source beats fighting the slider, so rescan flatter, or lift the contrast in any image editor first. There is also a privacy consequence worth knowing: only the small black-and-white bitmap is sent to our server, never your original photo.

Line drawings are not what you think they are

This is the single most misunderstood point. Vectorizing traces the outline of black areas, not the centre of lines. Feed it a drawing with 1 mm thick lines and you do not get one line back — you get a long thin closed loop running down both sides of it, because that is genuinely where black meets white. For a laser that cuts an outline, or for a stencil, that is exactly right. If what you actually wanted was a single centreline path for an engraving toolpath, that is a different operation called centreline tracing or skeletonisation, and most CAM packages can do it from this result or from the bitmap directly. Knowing which of the two you need before you start saves a great deal of confusion afterwards.

Scale is meaningless until you set it

The output has no idea how big your object is. An image knows pixels; it does not know millimetres. So the DXF arrives at whatever size the tracing produced, and you must rescale it in your CAD software before anything is cut. The reliable way is to include a known dimension in the scan — put a ruler beside the object, or measure one feature on the real part — then scale the drawing so that feature matches. Do this before you do anything else, because every subsequent measurement inherits the error. A drawing that is silently ten times too large looks perfectly correct on screen and only reveals itself at the machine.

Speckles, noise and the cleanup that pays for itself

Scanner noise, paper texture, JPEG artefacts and dust all become geometry, because the tracer has no way of knowing they are not part of your drawing. The result is a DXF containing your shape plus a few hundred tiny closed contours, each of which a cutting machine will faithfully try to cut. Reducing the threshold usually removes the faint ones. What survives is best deleted in CAD: most packages can select by size or by area, which turns a tedious job into a few clicks. It is genuinely worth doing before cutting rather than after, because a stray one-millimetre contour costs a pierce and a scorch mark on the finished part.

When to reach for this, and when not to

Use it for clean two-tone material: logos, signatures, stamps, stencils, silhouettes, simple traced sketches, an old paper drawing that only exists on paper. Do not use it to convert a photograph of an object into a CAD model — there is no algorithm here that reconstructs a shape from shading, and the result will be a mess of contours following the highlights. Also do not expect it to reproduce a technical drawing as a technical drawing: you will get the outline of every printed line including the dimension arrows and the text, as shapes rather than as annotations. If your source is a PDF rather than an image, start from the PDF instead, because a PDF often contains real vector paths that can be extracted directly rather than traced.

What this can and can't do

Vectorizing traces the outlines of black areas — it shines on clean line drawings, logos, stamps, stencils and signatures. It does not turn a photo into CAD geometry, and it doesn't measure your original: check and rescale the dimensions in your CAD program before cutting anything. The preview shows exactly which pixels will be traced — move the slider until the drawing looks crisp and the background is clean.