SIG Converter

What are SIG files?

SIG (Signature Image) is a raster format for storing a handwritten signature as a compact bitmap. In the files we have examined, the content is a standard baseline JPEG stream in which every pair of bytes is swapped: the header reads FJFI instead of JFIF, and the first bytes are D8 FF E0 FF instead of FF D8 FF E0. Once the byte order is restored, the file is an ordinary RGB JPEG with an optional embedded ICC color profile and a resolution of about 200 dpi, for example 880 by 233 pixels. This is why viewers that rely on the file signature cannot open it by default. Conversion reverses the swap and decodes the JPEG data, after which the signature can be saved as PNG with a transparent background, as JPEG or TIFF for printing, or as PDF for insertion into a document. Because the image is a scan with a white background, a conversion to PNG often includes thresholding the paper color to alpha so that the signature can be placed over text without a white box. The format does not store pen pressure, stroke order, or timing, so the file is a picture of a signature and not a biometric record.