Guidelines: Content Categories and Subcategories Objectives:
Reformatting Historical Printed Matter, Documents and Manuscripts,
and Pictorial Materials — Content Categories and Subcategories Table
Still Image Working Group

Use Cases: Master Images and Image Sets

• Digitizing organization uses archival or production master image(s) to produce derivative images for the use cases listed under the tab to the right.
• Digitizing organization uses the master image set (or an appropriate derivative image set) to create a virtual replica or a physical replica of the original item in the event of the loss, deterioration, or de-accessioning of the original.
• Digitizing organization (or successor/receiving agency with an archiving mission) sustains the master (or migrated copies) for the long-term without loss of essential features.
• Digitizing organization uses masters for disaster recovery in the event of impairment of digital asset management systems.

Quality Notes

• Image-quality characteristics of the archival or production master image(s) must be sufficient to support the production of the various image types listed under the Derivative Images tab. Dependencies include appropriate image specifications and a production activity that applies appropriate process controls, e.g., the use of targets to monitor output, a quality assurance process that includes the use of calibrated monitors and viewing environments, and various automated tools.
  
• For future exploration: When should master images be in an original-referred image state?
  
• In order to produce a virtual replica or a physical replica of the original item, the master "set" must possess three features: (1) the image-quality characteristics as cited above, (2) completeness of coverage (all pages, in some cases capture of paper sheet "beyond the edge," in some cases book covers and/or spines), and (3) structural metadata for the complete work.
  
• In order to sustain or migrate the master over the long-term without loss of essential features, the following features are required: (1) image-quality characteristics as above, (2) completeness of coverage and structural metadata as above, and (3) the selection of sustainable digital-content formats.
  
• Disaster recovery in the event of the impairment of digital asset management systems depends upon the availability of metadata in standardized formats, including embedded image-level metadata and work-level descriptive, administrative, and structural metadata.

Comments

Master and derivative image specifications for T.5 and T.6 include color, thus distinguishing them from the specifications for sub-categories T.1, T.2, T.3, and T.4.

Use Cases: Derivative Images and Image Sets

• Patron sees or reads inline image or image set in user interface. In some cases, users will seek viewing access to a complete work, in effect a virtual replica.
• Patron makes a hard copy of one or more images for personal use. In some cases, patron requires a print-on-demand copy of a complete work, in effect a physical replica, albeit in this case (scans from microfilm) a replica with moderate print quality.
  
• Patron is confident that the content received is an accurate and/or authentic reproduction of the original item.
• Patron (or content delivery system) receives information on rights and restrictions (delivery system may act on that information, if appropriate).
• Patron downloads one or more of the derivative images and, later, uses embedded metadata to identify the content and to determined technical and provenance information about the image.
• Patron examines the entire online image-set or a hard copy of the complete work (e.g., a book), to visualize it "as originally published."
• In some cases, digitizing organization runs OCR process to produce text. Patrons may read, search, or download this text for a variety of uses.
• Digitizing organization produces and archives an image that documents the condition of the original physical item in order to support its conservation.
• Publisher uses image to illustrate a book in color.
• Publisher uses image to illustrate a large color poster.
• Publisher uses image to create museum-quality color facsimile.
• Exhibit designer uses image for display "mural."
• Broadcaster uses image in high-definition television program, possibly with a Ken Burns effect.

Quality Notes

Inline image in user interface:

• Text is legible and graphic illustration content is reasonably clear. Zoom in may be required. In rare cases, legibility may depend upon contrast stretching.

Hard copy output:

• As good as a photocopy.

Patron confidence in accuracy and/or authenticity:

• Depends upon provenance metadata (attribute of the copy) and trustworthiness of the provider (attribute of the institution).

Images for OCR processing:

• Produce text at accuracy of 90 percent or higher.

Image to illustrate a book:

• Good enough to make a printing plate(s) for a one-ink-color of four-color printed halftone, 12x20 inches; if one ink color, 180 dpi/lpi.

Image for use as an exhibition mural:

• Good enough to make digital print, 6x9 feet.

Image for use in high-definition television program:

• Good enough to fill high-definition screen and zoom in (Ken Burns effect).

Note: Derivative images will generally be in an output-referred image state.

Recommended

Note: The 2004 NARA Guidelines also include alternate specifications similar to those below, but with reduced requirements for pixel density. These alternate specifications are not included here.

• 24-bit color mode - adjust scan resolution to produce a QI of 8 for smallest significant character

or

• 24-bit RGB mode - 400 ppi for documents with smallest significant character of 1.0 mm or larger

*NOTE: Regardless of approach used, adjust scan resolution to produce a minimum pixel measurement across the long dimension of 4,000 lines for 24-bit files.