From THO

THO Standards for Cultural Heritage Digitization Projects

Digitization Standards

Introduction

Presenting cultural heritage materials online requires conversion, whether from an original physical object to a digital surrogate, an analogue surrogate (such as microfilm) to a digital surrogate, or from one digital format to another. Creating digital surrogates from two-dimensional still images and texts is a relatively well-understood process, and several guides to best practices are available. Creating digital surrogates of three-dimensional objects and time-based media such as audio and video is less well understood. Participants should understand that this is an evolving field and that recommended practices may change over time, sometimes with the result that re-digitization will be required. In general, open standards are to be preferred over proprietary standards, as this may reduce the need for re-digitization in the future.

Excellent overviews of the digitization process can be obtained from the Cornell University Library's Moving Theory Into Practice: Digital Imaging Tutorial and from the Getty Institute's Introduction to Imaging (Revised Edition) by Howard Bessner, edited by Sally Hubbard with Deborah Lenert.

Levels of Digitization

THO recognizes three levels of digitization:

Minimal

Participants will provide online access to "reference" or access-quality digital objects, objects that are designed for use in the context of the World Wide Web. These objects may be images, texts, or multimedia documents, and may appear in any of the formats commonly supported by Web browsers. For specific formats and resolutions, refer to the Western States Digital Imaging Best Practices, Version 1.0, and CDP Digital Audio Best Practices, Version 2.0.

Some older collections may include materials that do not meet current standards, possibly because they were scanned using older standards or using equipment that was not capable of capturing sufficiently high resolutions or saving to uncompressed formats. Ideally, these objects would be re-digitized, but until such time as that is possible, they should be treated as meeting minimal standards.

Basic

Participants will create "master" or archival quality digital objects, objects that are saved in a lossless compression format at a sufficiently high resolution or sampling rate that the object is a "reasonable reproduction" of the original, without enhancement, as described in the 2004 NARA Technical Guidelines for Digitizing Archival Materials for Electronic Access. See the "Recommended Image Parameters" in the NARA Guidelines for specific minimum resolutions for text and still images. Technical metadata, including at a minimum EXIF data if generated by a digital still camera, will be created for each object.

In addition, participants will provide online access to "reference" or access-quality digital objects and to "thumbnails" of those access-quality digital objects. In the case of multimedia objects, thumbnails may be extracted from the original sequence or a "snippet" of the file may be provided for reference, and highly-compressed versions of the master object may be made available for streaming or download.

Enhanced

Participants will create "master" or "archival" quality digital objects that meet the requirements for a level 2 image quality assessment rating according to the NARA Technical Guidelines for Digitizing Archival Materials for Electronic Access. Detailed technical metadata about each object will be generated according to the NISO Z39.87 draft standard or its successor(s) and will be stored in both the image header, where possible, and in an external database. Participants may choose to create access-quality digital objects and "thumbnails" or "snippets" from the master object or may enable automated creation of such objects through digital library systems.

References

• Bessner, Howard, edited by Sally Hubbard with Deborah Lenert. 2003. Introduction to Imaging. Revised Edition. Retrieved 2 February 2006 from the Getty Institute’s website: http://www.getty.edu/research/conducting_research/standards/introimages/
• CDP Digital Audio Working Group. November 2005. Digital Audio Best Practices, Version 2.0. Retrieved 12 January 2006 from http://www.cdpheritage.org/digital/audio/documents/CDPDABP_1-2.pdf
• Cornell University Library. 2003. Moving Theory Into Practice: Digital Imaging Tutorial. Retrieved 2 February 2006 from http://www.library.cornell.edu/preservation/tutorial/.
• National Information Standards Organization, and AIIM International. 2005. Data Dictionary: Technical Metadata for Digital Still Images (NISO Z39.87-200X; AIIM 20-200X). Draft Standard. Retrieved 12 January 2006 from http://www.niso.org/standards/resources/Z39-87-200x-forballot.pdf
• Puglia, Steven, Jeffrey Reed, and Erin Rhodes. June 2004. U.S. National Archives and Records Administration (NARA) Technical Guidelines for Digitizing Archival Materials for Electronic Access: Creation of Production Master Files – Raster Images For the Following Record Types- Textual, Graphic Illustrations/Artwork/Originals, Maps, Plans, Oversized, Photographs, Aerial Photographs, and Objects/Artifacts. Retrieved 12 January 2006 from http://www.archives.gov/research/arc/preservation/digitizing-archival-materials.pdf
• Western States Digital Standards Group, Digital Images Working Group. 2003. Western States Digital Imaging Best Practices, Version 1.0. Retrieved 12 January 2006 from http://www.cdpheritage.org/digital/scanning/documents/WSDIBP_v1.pdf