What happens to a signature here
The Ink panel opens first. If the PNG is transparent, its alpha channel already marks the ink. If it is a scan or a phone photo, the paper is separated from the ink by brightness. Either way the picture is cropped to the ink, with a margin of 8% of the longer side so the strokes do not touch the frame.
White goes under everything, the edge repair is on so the strokes have no grey halo, and the quality is searched to land between 10 and 20 KB — the commonest signature rule. Pick 140 × 60 px or 4.5 × 2 cm at 200 DPI from the same panel, or choose a form under Form to take its exact rule.
Getting a clean result
- Sign in dark ink on plain white paper, and photograph it flat in daylight. Shadows across the page are the commonest reason the threshold needs moving.
- If the strokes break up, raise the threshold so lighter pixels count as ink.
- If grey specks of paper survive, lower the threshold a little until they become background.
- Under the minimum KB? Let the page find a larger pixel size, then check the form accepts it.
Questions about signatures
- Why is there a grey outline around my signature?
- The anti-aliased edge of each stroke is part ink, part whatever the signature was cut out of. Put on white, that leftover colour shows as a grey rim. The edge repair here gives those pixels the colour of the solid ink next to them before the white goes underneath, which is why it is on from the start.
- Why is my signature file too small for the form?
- A signature is mostly empty white, and white costs almost nothing to store, so a 140 × 60 signature can come out at six or seven kilobytes even at quality 100 — under a 10 KB minimum. The page says so with the figure and can find the smallest enlargement that reaches the floor. It never pads the file with junk.
- My signature is a photo of paper, not a transparent PNG. Does it work?
- Yes. With no transparency in the file, paper and ink are told apart by brightness: the threshold is chosen automatically for your picture (Otsu's method) and a slider lets you move it for faint pencil or a grey scan. Everything brighter than the threshold becomes the white background.
- Does the tool change my signature?
- It decides which existing pixels are ink and crops around them. It does not draw, smooth, generate or reshape a stroke.
- Is my signature uploaded?
- No. It is opened, cropped, put on white and encoded in this tab. Nothing about it leaves the page.
Next steps
- PNG to JPG for online formsThe photo for the same form, with its own rule and checks.
- PNG to JPG in KBAny other kilobyte range.
- PNG to JPG with white backgroundWhite held, for everything that is not a signature.
