How tracing works
Each pixel is first given a class. In Black and white that is ink or paper, by how dark it is against the Threshold; Auto threshold picks the level that splits the picture most cleanly (Otsu's method). In Colour the picture's colours are gathered into the number you choose, by k-means or median cut, measured in OKLab so that colours which look alike are grouped together. The edge of each region is then followed pixel by pixel, smoothed, split at sharp corners and fitted with Bézier curves, so a staircase of pixels becomes one clean line.
Getting a clean result
Logos, icons, line drawings and flat artwork trace best: a few solid colours with crisp edges. Remove specks folds tiny islands into the colour around them, which clears out noise and JPEG fuzz. A lower Corner threshold keeps more corners sharp; a higher one rounds them. Curve smoothing evens out wobbles, and Path simplification lets the curves stray a little further from the pixels for a smaller file. In Colour mode the shapes are stacked, biggest colour at the bottom and each layer reaching under the ones above it, so no hairline gaps open between neighbours. Lock palette keeps your colours while you change the other settings, and clicking a swatch changes that colour in the SVG.
Pixel art, and saving
Pixel art skips the curves: every pixel is kept as an exact square and same-coloured runs are merged into rectangles, so the SVG scales up perfectly sharp. It is meant for small pictures, up to 512 pixels on a side. Compare the result with the original with the slider or side by side, and zoom in to check the edges. Then download the SVG, copy its code into a web page, or save a PNG drawn from the SVG at one, two or four times the size.
Questions
Is my picture uploaded?
No. The tracing runs in your browser, in a background worker on your device. Nothing is sent anywhere and nothing is kept once you close the page.
Can it trace a photo?
It will, but a photo has thousands of soft colour changes, so the SVG comes out as a poster-like picture with many shapes and a large file. Fewer colours and more speck removal give a cleaner, smaller result. Tracing suits logos, drawings and flat art much better.
Why was my picture made smaller?
Very large pictures are traced at about 2,000 pixels on the long side to keep the page quick. The SVG still opens at your picture's full size, and being vector it stays sharp at any size.
Why are some colours slightly off?
Each traced colour is the average of the pixels grouped into it. Click a swatch under Palette to set the exact colour you want, such as your brand colour. To pick or convert colours, use the Color Picker.