Preservation

Digital File Types

Digital file types describe the types and characteristics of the files produced from the digitization of original record materials at NARA, as well as the standard or most common data formats that the Digitization Services Branch uses to store digitized records.

  • Still Image File

    A type of digital object that is created from the digitization of still image (textual documents and photographs) originals. A still image is data in which a grid or raster of picture elements (pixels) has been mapped to represent a visual subject, e.g., the page of a book or a photograph. The term raster data is often contrasted with vector data, in which geometrical points, lines, curves, and shapes are based upon mathematical equations, thus creating an image without specific mapping of data to pixels. [From the FADGI Glossary] Bit-depth, spatial resolution, and color encoding, for example, are all important characteristics of still images. Raster images can be stored in a variety of data formats, such as TIFF (.tif).

    • JPEG: Joint Photographic Experts Group

      JPG/JFIF (Joint Photographic Experts Group/JPEG File Interchange Format) is a popular file format for storing raster image data. JFIF is the file format; JPG is the compression method JPG/JFIF is specified in the JPEG File Interchange Format and JPEG (ISO 10918). The Sustainability of Digital Formats site at the Library of Congress contains additional information about the JFIF file format as well as JPG compression encoding.

      Currently, the Photographic Imaging, Microfilm and Textual Preservation Lab is using JPEG/JFIF (as well as TIFF) for most distribution files. JPEG files are well-suited for online access and use and are compressed for faster online transmission. JPEG files are created for use in NARA's Online Catalog as well as other internal databases, and for many reference requests.

      NARA's JPEG/JFIF files are identified as PUID fmt/44 in the PRONOM database.

      Although JPEG/JFIF is the formal full name of the file format (Joint Photographic Experts Group/JPEG File Interchange Format), the three character file name extension is JPG. We have used the three character file name here in keeping with he way the file format is most often expressed as a file name extension.

    • TIFF: Tagged Image File Format

      TIFF (Tagged Image File Format) is a popular format for storing raster image data and is specified in TIFF Revision 6.0 from Adobe Systems. Additional information about the TIFF file format can be found at the Sustainability of Digital Formats site at the Library of Congress.

      Currently, the Photographic Imaging, Microfilm and Textual Preservation Lab is using the TIFF file format for both preservation master and most reproduction master files. The TIFF file format is a stable, well-documented, widely adopted, uncompressed file format widely used for master files in the digital imaging community.

      NARA's TIFF files are identified as PUID fmt/353 in the PRONOM database.

      Although TIFF is the formal full name of the file format (Tagged Image File Format), the three character file name extension is TIF. We have used the three character file name here in keeping with the way the file format is most often expressed as a file name extension.

      • PDF: Portable Document Format

      PDF (Portable Document Format) is a popular format for storing many types of data including raster images. There are several subtypes of PDF including PDF-A. Additional information about the PDF format can be found at the Sustainability of Digital Formats site at the Library of Congress.

      NARA's PDF files version 1.4 and are identified as PUID fmt/18 in the PRONOM database.

      Currently, the Photographic Imaging, Microfilm and Textual Preservation Lab are using the PDF format for distribution purposes only.

  • Audio File

    An audio recording produced from original analog or digital audio formats that has been encoded using linear Pulse Code Modulation (PCM). For audio files, it is important to distinguish between a file format and a codec. A codec performs the encoding and decoding of the raw audio data while the data itself is stored in a specific audio file format, such as Broadcast WAV (.wav). Sampling frequency, bit-depth, and monophonic or stereo, for example, are important characteristics of audio files.

    • WAV: Waveform

      The Sustainability of Digital Formats site at the Library of Congress contains information about the WAV file format.

      NARA's WAV files are identified as PUID fmt/141 and fmt/142 in the PRONOM database.

      Although WAVE is the formal full name of the file format (Waveform Audio File Format), the three character file name extension is WAV. We have used the three character file name here in keeping with the way the file format is most often expressed as a file name extension.

    • MP3

      The Sustainability of Digital Formats site at the Library of Congress contains information about the MP3 file format.

      NARA's MP3 files are identified as PUID fmt/134 in the PRONOM database.

  • Video File

    A moving image recording with synched audio produced from either original analog or digital video formats. Pixel array, frame rate per second, aspect ratio, bit rate, field order, color space, and standard or high definition, for example, are important characteristics of video files.

  • Motion Picture File

    A high-resolution moving image recording, often with synched audio, produced from either original physical or digital formats. Bit-depth, pixel array, frame rate per second, and color encoding, for example, are important characteristics of motion picture files.

    • DPX: Digital Moving-Picture Exchange

      The DPX file format or Digital Moving-Picture Exchange is specified in SMPTE 268M-1994 and is a pixel-based (raster) image format in which each content frame is a separate data file linked by metadata to play in the correct sequence.

      NARA's DPX files are identified as PUID fmt/193 in the PRONOM database.

    • DCP: Digital Cinema Package

      A DCP or Digital Cinema Package is a collection of digital files used to store and convey digital cinema audio, image and data streams.

  • File Type To Be Determined

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