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10.0 Best Practices for Technical Metadata

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Introduction

Technical metadata is used for recording the technical attributes of digital objects that include their production or creation information on the digital capture process, i.e., the hardware and software used to acquire the digital object, file formats for master and derivatives, resolutions, color profiles and so on, that enable the reproduction of digital resources in the future. For this reason technical metadata is categorized as administrative and preservation metadata.

Technical metadata can be included in preservation metadata (PREMIS) or structural metadata (METS). The decision regarding where to add the technical metadata can be made based on the types of technical metadata that should be preserved since METS and PREMIS have different ways of incorporating technical metadata in its schema, as mentioned in Preservation Metadata and Structural Metadata Sections (see sections).

Table of Contents

 

10.1 Minimum Requirements

 

10.2 Object Types and Related Information

    10.2.1 Textual Document

    10.2.2 Still Image

    10.2.3 Digital Audio Files

    10.2.4 Digital Multi-Media Files

10.3 Tools that Capture Technical Metadata

     10.3.1 JHOVE

     10.3.2 XMP

     10.3.3 Exif

10.4 Resources

 

 

 

 

 

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10.1 Minimum Requirements

Requirements for technical metadata will differ for various media formats.  Regardless of media formats, all technical metadata should include the following information.

• File Format: Recommended best practice is to select a value from a controlled vocabulary, such as the list of Internet Media Types < http://www.iana.org/assignments/media-types/ > that defines computer media formats (also known as MIME types).

 

• File Size: For most formats, the recommended best practice is to record file size as bytes (e.g., 3,000,000 bytes) and not as kilobytes (KB), megabytes (MB), etc., because it is the most specific measurement of file size. It is also best practice to include duration time for multi-media. For example: 4,200,000 bytes; 5 minutes, 34 seconds.

 

 

10.2 Object Types and Related Information

10.2.1 Textual Document

There is a standard called textMD that is a XML Schema that details technical metadata for text-based digital objects <http://www.loc.gov/standards/textMD/>. It can be added into both METS (as an extension) and PREMIS. It can be also used as a standalone document.

When using the textMD schema, the technical metadata for text-based digital objects may include:

• encoding information (quality, platform, software, agent)
• character information (character set and size, byte order and size, line terminators)
• languages
• fonts
• markup information
• processing and textual notes
• technical requirements for printing and viewing
• page ordering and sequencing

10.2.2 Still image

For digital still image, it is recommended to use the NISO Data Dictionary - Technical Metadata for Digital Still Images at <http://www.niso.org/kst/reports/standards?step=2&gid=None&project_key=b897b0cf3e2ee526252d9f830207b3cc9f3b6c2c>.

The document includes metadata elements important to the management of image files that could be captured automatically from scanner or digital camera software. The elements are based on MIX. <http://www.loc.gov/standards/mix/>

The technical metadata for digital still image may include:

• file format

• file resolution (pixels per inch)
• dimensions (image dimension or size in inches or centimeters)
• bit-depth (e.g., 8-bit, 16-bit, 24-bit, etc.)
• color mode (e.g., RGB, CMYK, or grayscale)
• scanner or digital camera brand, name, and model number
• software used to manipulate or compress the image, including the software name and version.

10.2.3 Digital Audio Files

For digital audio files (sound only) the technical metadata for the image quality and the image capture process may include:

• file format, including whether the format is lossless or lossy
• sample rate
• resolution
• number of channels
• software used to manipulate or compress the audio file, including the software name and version
• brand, name, and model number of the recording equipment used.

10.2.4 Digital Multi-Media Files

For digital multi-media files (including video, sound, and animations) the technical metadata for the image quality and capture process may include the:

• file format
• bitrate
• software used to manipulate or compress the multimedia file, including the software name and version
• brand, name, and model number of the equipment used.

 

10.3 Tools that Capture Technical Metadata

 

Currently most of technical metadata can be captured automatically by digital camera or scanner. Followings are the most commonly used tools and standards used for extracting from or embedding metadata to the digital objects.

10.3.1 JHOVE

 

JHOVE <http://hul.harvard.edu/jhove/ > provides functions to perform format-specific identification, validation, and characterization of digital objects. JHOVE generates technical metadata about files, usually by extracting information from the files themselves.

10.3.2 XMP

Adobe's Extensible Metadata Platform (XMP) is a labeling technology that allows users to embed metadata into the file itself.  XMP is used for both descriptive (based on Dublin Core) and administrative metadata.

10.3.3 Exif

Exchangeable image file format (Exif) < http://www.exif.org/ > is a specification for the image file format used by digital cameras. Exif data is embedded within the image file itself and can be editable. The metadata tags defined in the Exif standard include, date and time information, camera settings such as the camera model and make, and information that varies with each image such as orientation (rotation), aperture, shutter speed, focal length, metering mode, and ISO speed information. A thumbnail for previewing the picture on the camera's LCD screen, in file managers, or in photo manipulation software, and Descriptions and copyright information can be also captured or added later.

10.4 Resources

• NISO Data Dictionary for Technical Metadata for Digital Still Images: http://www.niso.org/kst/reports/standards?step=2&gid=None&project_key=b897b0cf3e2ee526252d9f830207b3cc9f3b6c2c
• NISO Metadata for Images in XML: http://www.loc.gov/standards/mix/
• Technical Metadata for Text: http://www.loc.gov/standards/textMD/
• JHOVE: http://hul.harvard.edu/jhove/
• Exif: http://www.exif.org/
• IPTC Core and Extension: http://photometadata.blogspot.com/2008/07/iptc-core-11-extensions-10-released.html
• XMP: http://www.adobe.com/products/xmp/
• NARA Technical Guidelines for Digitizing Archival Materials for Electronic Access: http://www.archives.gov/preservation/technical/guidelines.pdf

Selected Resources for Technical Metadata

Source for File Format Extension Information:

http://www.fileinfo.com/

Additional file formats are listed at:

http://www.ace.net.nz/tech/TechFileFormat.html

U.S. National Archives and Administration. Technical Guidelines for Digitizing Archival Materials for Electronic Access: Creation of Production Master Files - Raster Images. (June 2004). Online Edition

http://www.archives.gov/research/arc/digitizing-archival-materials.html

National Information Standards Organization and AIIM International. NISO Data Dictionary - Technical Metadata for Digital Still Images http://www.niso.org/kst/reports/standards?step=2&gid=&project_key=b897b0cf3e2ee526252d9f830207b3cc9f3

California Digital Library

http://www.cdlib.org/inside/diglib/guidelines/bpgimages/

Collaborative Digitization Program (select section on digital imaging)

https://www.bcr.org

11.0 Best Practices for Structural Metadata

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Last modified by: Amy Bennett on 12/15/10