Transparent Signature Maker

About the Transparent Signature Maker

Sign a sheet of plain paper, take a photo, and get a transparent PNG of your signature to place on PDFs, letters, Word documents and e-signing apps. The paper, its texture and the shadow of your phone are removed with adaptive thresholding — every pixel is compared with its own neighbourhood, so uneven light does not turn grey paper into ink — and specks of dust are cleaned away. The pen strokes keep their soft, natural edge; the ink can stay as written or become black or blue, and the result is cropped round the signature.

For online forms there is also a white-background JPG at an exact pixel size and between a minimum and maximum file size in KB. Everything happens in your browser: your signature never leaves your device.

Common uses

• A transparent signature for signing PDFs, offer letters, invoices and contracts electronically.
• Signatures for letterheads, certificates, email signatures and presentations.
• A signature JPG at the exact pixel size and KB range an application form asks for.
• Cleaning up a scanned signature that shows paper texture or grey background.

How the paper is removed

A global threshold fails on phone photos: one corner is brighter than another, the phone casts a shadow, and paper is never pure white. This tool uses local (adaptive) thresholds instead:

• Sauvola (the default) — the threshold for each pixel is T = m × (1 + k × (s ÷ R − 1)), where m and s are the mean and standard deviation of the grey levels round it and R = 128 (J. Sauvola and M. Pietikäinen, “Adaptive document image binarization”, Pattern Recognition 33(2), 2000). Where the paper is even, only pixels clearly darker than their surroundings count as ink; the Sensitivity slider sets k from 0.5 (as in the paper) down to 0.05 for faint pencil or gel ink.
• Bradley–Roth — a pixel is ink when it is t% darker than the mean of a window an eighth of the image wide round it (D. Bradley and G. Roth, “Adaptive Thresholding using the Integral Image”, Journal of Graphics Tools 12(2), 2007; t = 15% in the paper, about Sensitivity 55 here). Try it when Sauvola leaves gaps in very thick strokes.

The local means come from running window sums — the same values as the paper’s integral image. Groups of ink pixels smaller than a speck (relative to the picture’s size) are removed. Next to the strokes, opacity runs from clear at the paper’s brightness to solid at the ink’s, so edges stay smooth instead of jagged.

Getting a clean result

• Use a black or dark blue pen on plain white paper; ruled or coloured paper may need a tight selection.
• Photograph in even daylight, without flash, and keep the phone’s shadow off the signature. The tool copes with soft shadows and uneven light, but not with a shadow darker than the ink.
• Fill the photo with the signature (or select it): the clean-up works on up to 2,400 pixels across the selected area (1,600 on phones), so a signature that fills the frame keeps the most detail.
• As written gives every stroke the median colour of your solid ink, so the result is even; choose Black or Blue when a form asks for a colour.
• Check the result on the Dark background: a light fringe round the strokes means the sensitivity can come down a little.

PNG for documents, JPG for forms

Transparent PNG keeps the transparency, so the signature sits on any page without a white box — place it with Sign PDF, or insert it as a picture in Word or Google Docs.

JPG on white is for upload forms that ask for a JPG within limits. With a width and height, the signature is fitted and centred on white at exactly that size. The quality is set as high as the maximum size allows; if the file is still below the minimum, an invisible JPEG comment pads it (the picture is unchanged). KB limits are met under either reading of a kilobyte — at most the maximum × 1,000 bytes and at least the minimum × 1,024 bytes. For the published sizes of IBPS, SBI, SSC, UPSC, NEET and other exams, use the Photo & Signature Resizer.

Limitations

• Works for dark ink on lighter paper; light ink on dark paper, and signatures over printed text or patterns, may need a careful selection or will not separate.
• Strokes as light as the paper (very faint pencil) cannot be told apart from it; sign with a darker pen.
• Shadows darker than the ink and creases may be kept as ink: retake the photo in even light.
• Use only your own signature, or one you are authorised to use. An image of a signature is not a certificate-based digital signature; whether it is accepted depends on the document and the organisation.

Privacy

Your signature is processed in your browser and never uploaded or stored. Only your choices of ink colour and file type are remembered on this device.