PNG to SVG: what tracing can and cannot recover

A bitmap remembers what colour every pixel ended up; a vector remembers the shapes that put them there. Converting PNG to SVG means running that process backwards — inferring shapes from their pixels — and like any reconstruction, it works exactly as well as the evidence allows. Knowing what survives the trip, and what never does, is the difference between a clean result and an afternoon of disappointment.

1. What tracing actually does

Every tracer runs some version of the same pipeline. First the image is posterised: every pixel is snapped to one of a handful of colours, because a tracer cannot draw a gradient, only regions. Then each colour's connected areas are extracted, and the boundary of each area is fitted with straight lines and curve segments. Specks below a size threshold are dropped. What comes out is one path per colour region — real geometry, but geometry invented from pixels, with node positions the fitter chose, not the ones a designer would have.

<!-- what the tracer saw -->
<path d="M31.8 12.1l.4-.1.9.4c.8.4 1.1.7 1.2 1.4l-.2 1.1 …" />

<!-- what the designer drew -->
<path d="M32 12 20 34h9l-3 12 13-20h-9Z" />

Both render a lightning bolt. One is eleven commands you can edit; the other is a faithful record of antialiased edges. The PNG to SVG tool runs this pipeline in your browser — posterisation level and speck threshold are the two knobs that matter, and the presets are those knobs in three arrangements.

2. The input decides more than the settings

A tracer amplifies whatever it is given. Feed it the sharpest, largest, cleanest copy of the image that exists, and spend your time hunting that copy rather than tuning sliders:

• Prefer PNG over JPEG sources. JPEG compression scatters faint ringing around every edge. Your eye ignores it; the posteriser does not, and edges come out wobbling. If a screenshot is all you have, screenshot at 2× and let the tool downscale.
• Do not upscale first. Interpolation invents no information — it makes the file bigger, not sharper. Tracing a 200 px logo blown up to 2000 px gives you the same shapes with smoother-looking mistakes.
• Crop to the artwork. Background texture, drop shadows and photo grain all become colour regions the tracer dutifully outlines. Remove what you do not want vectorised before it gets the chance.

3. Three kinds of image, three outcomes

Whether tracing pays off is decided by what the image is, more than by any setting:

• Flat artwork — logos, icons, diagrams — traces well. Few colours, hard edges, large regions: exactly the evidence a tracer needs. This is the case the whole exercise exists for.
• Text traces badly, always. Letterforms are precision shapes your eye knows intimately, and a fitted outline of 12 px pixels is never that shape. If you can identify the font, delete the traced text and set the words again with Text to Path — real outlines from the real font beat any trace.
• Photographs do not vectorize. A photo posterised to eight colours becomes hundreds of jagged fields, usually heavier than the JPEG it came from. The exception is deliberate: a poster-style portrait at four to six colours is a look, chosen on purpose, not a conversion.

4. The trace is the start, not the result

A raw trace ships with debris: halo colours where antialiasing blended foreground into background, stray specks the threshold let through, and coordinates quoted to absurd precision. The cleanup sequence that works:

• Merge the halos. Reduce the colour count until the invented blend colours collapse into their neighbours, or swap them explicitly with the Color Replacer afterwards.
• Delete what should not exist. Open the result in the editor, walk the layer tree, and remove stray paths — a trace's mistakes are much easier to spot in a layer list than on the canvas.
• Then optimise. The Optimizer rounds the coordinate precision and strips what the tracer left behind; on traced output the savings are routinely half the file. Why that works is its own story — why your SVG is 40 KB.

5. When redrawing beats tracing

Tracing is a reconstruction, and sometimes reconstruction is the wrong tool. A mark made of a few geometric shapes — circles, rounded rectangles, a chevron — is faster to redraw at full precision than to un-wobble node by node. An hour spent cleaning a trace is a redraw with extra steps, minus the precision.

And before either: check the vector original is actually gone. The agency that made the logo has the .ai file. The slide deck was exported from something. Marketing has a brand folder nobody looked in. The best trace is the one you never had to run — tracing is for when the search genuinely comes up empty.