About Image Vectorizer (PNG to SVG)
Tracing is done by VTracer, an open-source engine that runs as WebAssembly in a background thread of your browser. It finds regions of similar colour, stacks them into layers and fits curves to their edges, which is why a flat logo comes back as a few crisp paths while a photograph becomes a painterly mosaic of many. Pick the preset that matches the picture and the sliders start in the right place.
A raster image is a grid of pixels; a vector is a list of shapes. Converting one into the other means deciding where the shapes are, and that is what a tracer does: it groups neighbouring pixels of similar colour into regions, discards regions too small to matter, and fits curves to each region's outline. The result scales to any size without blurring, can be recoloured in a text editor, and is usually far smaller than the bitmap it came from — for artwork that was drawn as shapes in the first place.
The engine here is VTracer, from the visioncortex project. It differs from the older Potrace in two ways that matter for everyday use: it handles colour rather than only black and white, and it stacks the colour layers on top of one another instead of cutting holes, which keeps the SVG compact and free of hairline seams between adjacent shapes. It was built to trace high-resolution scans of blueprints, so a logo is well within its comfort zone.
Three presets set the sliders for the three kinds of picture people actually bring. Black & white thresholds the image to two tones first, which is right for scans, signatures and single-colour marks. Poster keeps a handful of flat colours with crisp boundaries, which suits logos, icons, illustrations and screenshots of interfaces. Photo keeps many layers with softer edges and produces a painterly result — larger, slower, and pleasant, but never a substitute for the photograph.
The sliders are the same controls the engine exposes, described in plain words. Filter speckle drops any patch smaller than a given number of pixels, which is how JPEG grain and scanner dust vanish. Colour precision and layer difference decide how many distinct colours survive and how far apart two colours must be to become separate layers. Corner threshold is the angle at which a bend becomes a sharp corner rather than a curve, and simplify is the tolerance in pixels for straightening a path — raise it for a smaller file, lower it for fidelity.
Work is done in a background thread of the page, so the interface stays responsive while a trace runs, and the image is scaled to at most two megapixels before tracing. That cap is deliberate: on a single thread a spline trace of a photo at that size takes a few seconds, and a vector gains nothing from more pixels — outlines do not get better past the resolution at which they were drawn.