Signature Extractor

Features

• Separates ink from paper automatically, even on off-white paper or in uneven light
• Five manual threshold steps, from light to heavy ink
• Four edge softness steps: smooth for photos, hard for scans
• Force black, pen blue or red ink — fixes the grey look of photographed black
• Trims the empty margins, leaving only a small border
• Invert mode for light ink on dark paper
• Can produce a white-background version for forms that cannot take transparency
• Says what to do when no ink is found, rather than returning an empty transparent image
• The image is never uploaded and no server is involved

How to use

1. Sign on white paper with a dark pen and take a clear photo (cleaner background is better)
2. Drop the photo in
3. The defaults usually work; adjust the threshold and edge softness if not
4. Download the PNG and paste it into your document or form

FAQ

My extracted signature keeps a grey background, or parts of a stroke are missing.

A lingering background means the threshold is too low and paper is being counted as ink — switching to Automatic usually fixes it, since Otsu re-finds the split for this particular photo. Missing strokes are the opposite: the threshold is too high and lighter strokes are read as paper, so step it down (150 or 120). Very high edge softness can also make thin strokes fade — if the tail of your signature is fine, drop it to 8.

Why does my signature show a black background in Word?

That is Word rendering the transparent area as black, which some versions and view modes do. The image is fine, but there is a safe workaround: switch the background option to White and download that version, which cannot display as a black block anywhere. If the document itself is dark, keep the transparent version and ignore Word's preview — it prints correctly.

How is the automatic threshold worked out? Why not just ask me for a number?

It uses Otsu's method: build a histogram of the brightness across the image and find the split that separates the pixels into two groups as far apart as possible. Paper and ink are exactly two such groups, so this almost always lands in the right place without needing to know how white the paper is or how bright the light was. The manual steps are for the exceptions: very light ink, or a large shadow across the paper, where the automatic value drifts to one side.

Is the signature image uploaded?

No. Processing uses the browser's own canvas entirely in local memory. A handwritten signature carries the legal weight of a contract or an ID, which makes it one of the last images that should pass through someone else's server. The tool keeps working offline, which is the proof that nothing is being sent.