Transparent Signature

A signature saved as a plain photo carries its paper with it: a grey or cream rectangle that shows on top of the document you sign, over its lines and its text. With the paper gone, only the ink lands on the page, as if you had signed it there.

The same file works in a PDF signing tool, a Word or Google Docs letter, an email signature or a contract template, and on any colour of background.

Paper is rarely pure white: under a lamp it turns cream, in the shade grey. So the colour to remove is the most common colour along the picture’s edges, where only paper is. Every pixel is then measured against it: close enough and it becomes see-through, far enough and it stays as it is.

Between the two, at the edge of each stroke, a pixel is partly see-through, and the paper’s share is taken out of its colour. That keeps the pen’s soft edge and its true colour, so blue ink stays blue on any background rather than turning grey at the edges.

Sign on plain white paper with a dark pen, and photograph it flat, in even light, filling most of the frame. A shadow across the page is the usual trouble: the darker corner is further from the paper’s colour and may stay. Raise Tolerance until it goes, or crop the shadow away first with Crop.

If faint strokes disappear, lower Tolerance; if a grey haze stays around the ink, raise it. Soft edge decides how gradually the ink fades into the transparency.