Format introduced by Sigma SD9 and SD10 digital camera. The Sigma DP1 uses it with some variations.
Official spec: http://www.photofo.com/downloads/x3f-raw-format.pdf (via the Internet Archive) - local copy
But the RAW data is “encrypted”. dcraw has code in GPL but no documentation per see. [http://www.photofo.com/x3f-raw-format/] (https://web.archive.org/web/20131126184040/http://www.photofo.com/x3f-raw-format/) (via the Internet Archive) is a project to try to document this.
- X3F Foveon, the Foveon partial documentation (via the Internet archive - 2007-08-07).