From: http://en.wikipedia.org/wiki/Digital_Picture_Exchange

Digital Picture Exchange (DPX) is a common file format for digital
intermediate and visual effects work and is an ANSI/SMPTE standard
(268M-2003). The file format is most commonly used to represent the
density of each colour channel of a scanned negative in a 10-bit
uncompressed log format where the gamma of the original camera
negative is preserved as taken by a film scanner. Other common video
formats are also supported. DPX provides a great deal of flexibility
in storing color and other information for exchange between production
facilities. Multiple forms of packing and alignment are possible.

The DPX file format was originally derived from the output file format
(.cin) of the Kodak Cineon 'FIDO' film scanner, and has been published
by SMPTE as ANSI/SMPTE 268M-2003 (originally was version 1 268M-1994).