|Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact
|Digital Moving-Picture Exchange (DPX) Format
File format for the exchange of resolution-independent, pixel-based (bitmapped) images, intended for very high quality moving image content for theatrical distribution; DPX masters provide the input for film recording (digital images back to film for projection) or D-Cinema digital projection systems. Each DPX file represents a single image with a single component, e.g., luma, or multiple components, e.g., red, green, blue; or Cb, Y, Cr (chroma-luma data). Many variations in multiple component data are supported. DPX images may be produced by scanning film or by using a camera that produces a DPX output.
DPX is intended to carry picture data; its developers assumed that sound would be carried in separate formats, e.g., WAVE files, and this is the general practice. Nevertheless, a few organizations scan an image area large enough to include optical soundtracks and at least one software application (AEO Light) can convert this image data to sound.
|Typically a middle-state format for material exchange, "post-production" in movie industry parlance, or archiving; in some circumstances may be a initial state format, i.e., "production," when digital cameras are employed.
|Relationship to other formats
|Has earlier version
|Digital Moving-Picture Exchange (DPX), Version 1.0 1994. See Notes for changes between versions.
|LC experience or existing holdings
|Used for motion picture scanning by the Motion Picture, Broadcasting, and Recorded Sound Division, beginning in 2004.
|None at this time.
|Open standard. Developed by the Society of Motion Picture and Television Engineers (SMPTE), a member of the American National Standards Institute (ANSI).
|SMPTE 268M-2003, SMPTE Standard for File Format for Digital Moving-Picture Exchange (DPX), Version 2.0
|Reasonably well adopted including US National Archives and Library and Archives Canada. Several film scanners support DPX, and it is offered as an output from ARRI, Kinetta and DALSA cameras among others. ImageMagicK supports editing of DPX files. On the playback side, FFmpeg has good support for DPX. It is not supported currently by popular viewers such as VLC or Windows Media Player.
|Licensing and patents
|Wrapper is transparent; overall transparency depends upon the essence encoding.
DPX is a pixel-based (raster) file format with attributes defined in a binary file header. Each file represents a single image or single frame of a motion picture or video data stream. Since each DPX frame is "one of tens of thousands" in a motion picture, users will track intellectual/bibliographic metadata separately from the set of DPX files. A DPX file has four sections (including one optional section):
|Technical protection considerations
|DPX files are not be designed to play in the customary sense. Most applications in which DPX files may be played will be professional; this is not a format intended for desktop PC applications.
|Clarity (high image resolution)
|Depends upon picture size and bit depth; for uncompressed bitmaps. The format has no limit on picture size (beyond that imposed by the use of 32-bit integers); many motion picture applications work at 2K (2048x1080 pixels) and 4K (4096x2160 pixels) resolution. Several color space implementations are supported. Regarding bit depth (necessary to encompass the wide dynamic or brightness range of actual scenes or images on film), many in the motion picture industry advocate having masters with 16-bit-per-channel linear data, whether RGB, YUV (chrominance-luminance), or some other, e.g., raw data from a Bayer array.
|Functionality beyond normal rendering
|Not investigated at this time.
|From the specification
|Internet Media Type
|Not registered with IANA. Found on FileSuffix.com
|If big-endian (most significant byte first), from the specification
|If little-endian (least significant byte first), from the specification
|Wikidata Title ID
|No versions declared. See https://www.wikidata.org/wiki/Q527723.
The European PRESTO project supported efforts to preserve broadcast content via digitization. A PRESTO report on a file format conversion software issued in 2002 includes two statements that pertain to DPX: "Currently the DPX file format has become an industry standard for film production. It supports resolution independence (spatial and densitometric), but does not meet the requirements of broadcasters because, for instance, it does not contain sound data or metadata. Film is stored as a number of single uncompressed image files. The MXF format intends to overcome these limitations by, for instance, support of metadata and by support of film structure information (shot information)." (p. 2)
The PRESTO report also includes a paragraph that indicates one application's approach to filenaming with one-frame-at-a-time formats like DPX, a critical issue since 30 minutes of film contains 43,200 frames and 30 minutes of video contains about 54,000: "Both input and output image sequences are expected to be stored as a number of files in the same directory in one of the following image formats: TIFF, PNM, SGI, RGB, DPX. Interlaced image sequences [video fields] are expected to be stored as a sequence of images containing two woven fields. The filename is assumed to be in the format name.n.ext, where n is the frame number with up to 8 digits and ext is the file extension. The number of digits in the frame number has to be constant for all frames of one sequence." (p. 13) Frank Wylie of the Library of Congress Film Preservation Laboratory confirms that most DPX-capable applications provide this type of filenaming as the default.
Stream and File Formats: Where Are We Now? states that DPX "was developed several years ago to support the transfer of uncompressed images between telecine machines. It was later used for synthetic image file transfers." The Wikipedia article on DPX reports (on December 5, 2013): "The DPX file format was originally derived from Kodak Cineon open file format (.cin file extension) used for digital images generated by Kodak's original film scanner." This format was referred to as Cineon.
As near as the authors have been able to determine, the content differences between DPX v.1 (SMPTE 268M-1994) and DPX v.2 (SMPTE 268M-2003) specifications are, in summary, updating references to other SMPTE standards and assigning previously reserved file space for specific purposes. This document does not detail all the changes in references to external SMPTE or other standards. However the substantive content changes between the v.1 and v.2 standards are listed below:
Moreover, Amendment 1 to DPX v.2 (SMPTE 268M-2003),was published in 2012. A summary of key changes are listed below:
Finally, the SMPTE Standards Quarterly Report (link available through Internet Archive) from March 2015 indicates that the latest revision of the DPX v. 2 standard, SMPTE ST 268:2014 was found to contain "significant errors ...[and] a corrected version is being put together." The authors of this website will wait until a stable version is released before conducting any analysis.
Federal Agencies Digital Guidelines Initiative Audio-Visual Working Group has drafting guidelines for embedding metadata in the DPX header. The draft guidelines outline FADGI implementations of the SMPTE Core fields as well as other elements Strongly Recommended, Recommended or Optional for FADGI use. The non-Core fields take advantage of existing header structures as well as define new metadata elements for the User Defined fields to document, among other things, digitization process history. The draft guidelines and supporting documents are now available for public comment through February 2017.