Signature Background Remover

What this signature background remover does

This page pulls the pen strokes out of a photo or scan of a signed sheet of paper and makes everything else transparent. It does not run the AI subject-segmentation model that the general background remover uses, and that is a deliberate design decision rather than a missing feature. A salient-object model asked to name the subject of a photograph of a signed page answers: the page. It would hand back the whole sheet, neatly cut away from your desk, with the signature still sitting on opaque white. Separating ink from paper is a different measurement entirely, so this page runs a different algorithm. It works the way a document scanner does. First it builds a map of how bright the paper is at every point, by averaging the brightness of a large square window around each pixel — a window sized at roughly one sixteenth of the shorter edge, computed through a summed-area table so the cost does not grow with the window size. Pen strokes are thin, so they contribute only a few percent of any such window, which makes that map a good estimate of the paper on its own, including its shadow gradient, the warm cast of a desk lamp and the yellowing of old stock. Each pixel is then judged against its own local paper value instead of against a fixed brightness: anything below the threshold share of the light around it becomes ink, everything else becomes transparent. A soft band immediately below the threshold keeps the antialiased outside of each stroke partly transparent, which is what stops the result from looking like a fax. Ink is flattened to near-black by default, or keeps its scanned color for a blue pen. The limits follow directly from the method: anything genuinely darker than its surrounding paper counts as ink, so printed text, ruled lines, graph squares, staple shadows and a hard crease all survive alongside the signature. A pencil signature barely darker than the sheet may need the threshold raised before it registers, and raising it also starts admitting paper grain. And because the illumination map assumes strokes are thin relative to the window, a thick marker signature filling most of the frame will partly erase its own interior. Output is always PNG, and the file never leaves your browser.