Guidelines: Embedding Metadata in DPX Files
Audio-Visual Working Group
Embedded metadata can travel with a digital object during its life cycle and often exists in synergy with metadata in an organization's databases or other information technology systems. Embedded metadata enables people in and outside an organization to work more efficiently, provides valuable data to the systems that preserve digital content, and can assist in disaster recovery. In addition to this project to develop guidelines for DPX files, FADGI offers embedding guidelines for WAVE audio files and two embedding guidelines for still images: for minimal descriptive metadata and for the TIFF header. In addition, the Working Group has developed the BWF MetaEdit tool to support users of the WAVE format.
Overview of DPX Format
Digital Picture Exchange (DPX) is a pixel-based (raster) file format intended for very high quality moving image content with attributes defined in a binary file header. There are two versions of the DPX format, version 1 defined by SMPTE 268M-1994 and version 2 defined by SMPTE 268M-2003 and Amd. 1:2012. DPX images are produced by scanning motion picture film or by using a camera that produces a DPX output.
Each DPX file represents a single image or frame in a sequence of a motion picture or video data stream 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. As a structured raster image format, DPX is intended to carry only picture or imagery data with corresponding sound carried in a separate format, typically WAVE files. In practice, this means that a single digitized motion picture film will consists of a sequence of tens of thousands of individual DPX files, each file corresponding to a frame of scanned film with sequentially numbered file names as well as a separate audio file for sound data.
FADGI Guidelines for Embedded Metadata in DPX Files
In spring 2016, FADGI Audio-Visual Working Group initiated a project to review the state of embedded metadata in DPX headers from a wide variety of film scanners in use at federal agencies and beyond. The results of the analysis demonstrate that metadata implementation is inconsistent, even in SMPTE core fields.
FADGI has authored 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.
This document is limited in scope to embedded metadata guidelines and does not look to define other technical characteristics of what a DPX file might carry such as image tonal settings, aspect ratios, bit depths, color models and resolution. Recommended capture settings are defined for a variety of source material in the companion FADGI document, Digitizing Motion Picture Film: Exploration of the Issues and Sample SOW.
This project is led by the FADGI Film Scanning subgroup with active participation from the Smithsonian's National Museum of African American History and Culture (NMAAHC), the National Archives and Records Administration (NARA), and the Library of Congress including Digital Collections and Management Services, the Packard Campus for Audio-Visual Conservation and the American Folklife Center. Many other agencies also participate, including the National Air and Space Administration (NASA).
DRAFT Guidelines for Public Comment
FADGI sees the value of publishing the preliminary version of the draft guideline so that the working group can get stakeholder comments early in the project.
- Embedding Metadata in Scanned Motion Picture Film Files: Guideline for Federal Agency Use of DPX Files (PDF, December 16, 2106). Comments welcome through February 28, 2017
- Anonymized analysis of embedded metadata and data structure in sample DPX files. (XLSX File)
Last Updated: 01/03/2017