Signature Background Remover

Turn a phone photo or scan of a signed sheet of paper into clean black strokes on a transparent PNG, with the paper, its shadows and its yellow cast gone.

将图片拖放到此处或点击上传

支持 JPG、PNG、GIF、WEBP、SVG

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.

Why a signature needs its own tool

Almost nobody signs digitally on the first pass. The normal sequence is that a contract, a lease, a tax form or a school permission slip arrives as a PDF, someone prints the signature line or signs a blank sheet, and then photographs it with a phone because there is no scanner in the house. What comes back is a rectangle of paper that is bright near the window and grey in the corner, slightly warm from the ceiling light, with a faint shadow from the hand that held the phone. Dropping that rectangle into a document leaves an obvious pale patch sitting on top of the page, and it reads as exactly what it is. What the document actually needs is the strokes and nothing else, so the underlying text and rules show through around the signature the way they would if it had been signed on the printout. That is also why the general background remover is the wrong stop for this job: it removes what is behind the paper, not what is behind the ink. The relative threshold matters for the same practical reason. A single fixed brightness cutoff can be tuned for one photo and then fail on the next one taken two minutes later from a different angle, because the paper in the shadowed corner of the second photo is darker than the ink in the bright corner of the first. Comparing each pixel against its own neighbourhood makes the setting transferable, which means you can sign five forms, photograph all five under the same messy lamp, and run them through without retuning. Everything happens in the browser, which matters more here than on most tools: a signature is one of the few images where uploading a copy to somebody else's server is a genuine risk rather than a theoretical one.

Local paper-brightness comparison, so uneven lamp light and shadow do not break it

Works on yellowed, warm-cast or off-white paper without a color correction step

Strokes flattened to near-black, or the original pen color kept on request

Transparent PNG that sits on a contract without a visible paper patch

How to get a clean signature cut-out

The result depends more on how the page is captured than on the settings, so the first two steps matter most.

Sign a plain unlined white sheet with a dark pen, and photograph it flat from directly above so the signature fills most of the frame — a distant shot leaves too few pixels per stroke to threshold cleanly

Upload the photo or scan; nothing is sent anywhere, the file is read locally

Press Extract signature, then check the result against the white and dark backdrops — a light halo only shows on the dark one

If strokes are broken raise the ink threshold, if paper grain shows lower it, then download the transparent PNG

Frequently Asked Questions

Because the AI model finds subjects, and on a photo of a signed page the subject is the page. Running it gives you a cleanly cut-out sheet of paper with the signature still on opaque white, which is the opposite of what you need. This page instead measures how bright the paper is around each pixel and keeps only what is meaningfully darker than it. If your sheet happens to be photographed on a patterned desk or held up against a room, you can turn on the optional paper-isolation pass, which runs the AI model first to get rid of the scene and then applies the ink threshold to the sheet.

Not much, and that is the main thing this page is built for. A single fixed brightness cutoff cannot handle it: in a strongly lit photo, the paper in the shadowed corner can be darker than the ink in the lit corner, so no single number separates the two. Every pixel here is compared against the average brightness of a large window around itself instead, so the shadowed corner is judged against shadowed paper. Very harsh light with a hard shadow edge crossing the signature is still worth avoiding, but a normal desk-lamp gradient is handled without any adjustment.

That is expected and unavoidable with this approach. The tool has no concept of a signature; it keeps whatever is darker than its surrounding paper, and printed text, ruled blue lines, graph squares, a staple shadow or a hard fold all qualify. The fix is at capture time: sign a blank unlined sheet, or crop the photo down to just the signature before uploading so nothing else is in frame. Lined paper specifically is worth avoiding, because the lines are usually close in darkness to a light pen stroke and no threshold setting will separate them.

Pencil sits much closer to the paper brightness than ink does, so it needs the ink threshold raised — try moving it upward until the strokes fill in. The cost is that paper grain starts to register at the same time, because grain is also slightly darker than its surroundings. If pencil is all you have, capture it at the highest resolution you can and under even light, since both raise the contrast between graphite and paper. A dark ballpoint or fineliner will always give a cleaner result than pencil.

Around 20 for anything that will be scaled down, which is most uses. That keeps a partly transparent band on the outside of each stroke, so when the signature is shrunk to fit a signature line it still reads as pen rather than as a jagged shape. Drop it to 0 only if you need a strictly two-level image, for example because you are feeding the PNG into something that treats any partial transparency as opaque. Above about 40 the band starts pulling in genuine paper and the strokes look smudged.

Yes, turn on the option to keep the original pen color. It is off by default because black ink photographed by a phone rarely comes out black: the camera white-balances against the paper and returns a washed grey-brown that looks faded once it sits on a white document. Flattening to near-black fixes that in the common case. For blue, red or any deliberately colored ink, keeping the scanned color is the right choice, though the color you get is whatever the camera recorded rather than the true ink color.

Nowhere. The image is decoded, thresholded and re-encoded inside the page using the browser canvas, and no copy is sent to any server. The one exception is the optional paper-isolation pass, which downloads an AI model file to your device on first use and then also runs locally; even then the image itself is not transmitted. This is worth being specific about for signatures in particular, since a signature is one of the few images where a stray server-side copy is a real problem rather than a hypothetical one.

All three end in a transparent PNG, but they solve different problems. Remove Background and Transparent Background both run AI subject segmentation and are for photos with a subject — a person, a product, an object. This page runs no segmentation by default and is for flat documents, where the thing you want to keep is thin dark marks on a light surface. If you want to draw a signature with a mouse or a finger rather than photograph one on paper, the signature drawing page is the better starting point.

What this signature background remover does

Why a signature needs its own tool

How to get a clean signature cut-out

Frequently Asked Questions

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