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Home > Guidelines > Content Categories & Digitization Objectives > Explanatory Notes

Guidelines: Content Categories & Digitization Objectives Explanatory Notes
Still Image Working Group

General Explanatory Notes

About the Categories and Subcategories

The six main categories (T, PR, PT, AR, AT, and 3D) and their 23 subcategories represent the broad realm of printed matter, documents and manuscripts, pictorial materials, and three-dimensional objects and artifacts. Content in these categories and subcategories may be found in libraries, archives, galleries and museums, and among the administrative records of government agencies. These categories and subcategories were inspired by similar categorizations found in the 2004 National Archives and Records Administration (NARA) publication Technical Guidelines for Digitizing Archival Materials for Electronic Access, p. 45 (scanning from microfilm) and pp. 51-59 (all other subcategories).

Categories SPA and SPR are placeholders for descriptions of specialized imaging that are not customarily part of library and archive reformatting and the Working Group is not developing information about them at this time. SPA and SPR do not reference distinct types of original or source materials like the six categories listed in the preceding paragraph. Category SPA pertains to the creation of images of works of fine art, broadly speaking, including three-dimensional works, by means of specialized and complex approaches that are custom-fitted to the work at hand. Category SPR pertains to the creation of specialized images for analysis and research regarding the physical properties of the item being imaged. SPR is also a placeholder for the large and important category of born-digital (i.e., not reformatted) scientific and medical imaging, carried out by a number of federal government agencies.

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Matching Original Prints, Retaining Functionality for Photographic Negatives

In most cases, a high-level goal for digital images that reproduce reflected-light items (e.g., a printed book or a photographic print) and some positive transmitted-light items (e.g., photographic color slides) is to "match" the original. It is important to remember that the derivative images, rather than the master images, will provide the match expected by the end-user. In order to accomplish this objective, derivative images may require different tonal or resolution characteristics than the masters. In addition, the characteristics of an image that provides a match on a computer monitor may differ from those of an image that provides a match in hard copy.

When reformatting photographic negatives (and some transmissive positive originals), the objective may not be to match the original. Instead, the goal may be to produce a digital image that can provide the same functionality as the original. In such cases, the digital master will serve the same purpose as a photographic interpositive, duplicate negative, or duplicate transparency.

Analog photographic negatives--whether the original or a duplicate--are used in a darkroom to produce prints that vary according to their purpose. Such prints may have rich tonality and deep blacks for the gallery wall or lighter shadow areas for reproduction in a book or magazine. In a digital operation, this type of variation is achieved by using the master to produce derivative images that meet the requirement at hand.

The digital reproductions of photographic negatives and transparencies may also be used to support forensic study or to serve other types of analysis. For example, a legal researcher may wish to manipulate tonal representation in order to "see into the shadows" of a police photo. The image may contain hidden detail that reveals evidence related to a criminal case. In a similar use case, a radiologist may be better able to detect a tumor by adjusting the brightness or contrast of an image display when examining an x-ray. In our statements of objectives, use cases like these are represented by the patron who studies details in the deep shadows of Civil War field tent or the researcher looking into the shadows of an aerial photograph. In the digital realm, the ability to "see into the shadows" is enhanced by providing the researcher with a high dynamic range image.

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About Master and Derivative Images

The term master in this presentation refers to both the archival master file and the production master file. One or the other of these files will be used to execute the use cases listed under tabs labeled master. The term derivative images refers to any of a number specialty images that may be produced to meet the various objectives listed.

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About Digital Imaging Objectives and Use Cases

Reformatting objectives are provided for each of the 23 subcategories under the six main categories (T, PR, PT, AR, AT, and 3D). These objectives represent the goals of the organizations that carry out the digitizing and also the objectives of the endusers who will consult or use the images in their work.

The objectives are stated as simplified use cases: they name an actor (in a certain role) and an action that represents a use of the image. In many instances, use cases are phrased in singular terms but they are intended to represent larger classes. For example, "publisher uses image to illustrate a book" should be understood as pertaining to a number of publishing applications, in a variety of print outlets. Think of these use cases as "for instances."

Some use cases refer to an image set. This refers to the entire set of images resulting from the digitization of a complete work, e.g., all of the images for the pages in a book that has been scanned.

The wording for use cases is often identical from one category to the next. For example, the use case publisher uses image to illustrate a book appears in these tables several times. The image specifications that will satisfy the publisher, however, will differ from category to category. A bitonal image will permit a publisher to reproduce a simple typographic document as line art (subcategory T.1). In order for the same publisher to print an legible image of a handwritten manuscript, an uncompressed grayscale image (subcategory T.3) will be required. To print, say, a water color painting in a fine art book, a high-resolution uncompressed color image (e.g., categories PT.2 or PR.2) will be required.

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Long-Term Preservation

For all categories, the use cases for master images include a pair that pertain to the preservation of content for the long term:

  • Digitizing organization uses the master (or migrated copies) to create a virtual replica of the original item in the event of its loss, deterioration, or de-accessioning.
  • 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.

These objectives make a good fit for agencies with a long-term preservation mission. What about organizations that do not have such a mission, such as agencies in the Executive Branch whose records will ultimately be transferred to the National Archives and Records Administration? Some portion of their image holdings may be considered to be official records that will be transferred in the future. Such a transfer to a permanent archive is what is intended by the parenthetical phrase “successor/receiving agency with an archiving mission” in the second objective above. In these cases, it is very desirable for the originating agency to produce preservation-ready images that can subsequently be transferred to their permanent home.

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Image Specifications and the NARA Guidelines from 2004

At this writing (2009), the Working Group has begun the process of developing recommended specifications and practices to be associated with these tables. As a placeholder, this Web presentation presents the digitization recommendations found in the important 2004 National Archives and Records Administration (NARA) publication Technical Guidelines for Digitizing Archival Materials for Electronic Access, p. 45 and pp. 51-59. These can be seen an interim set of baseline specifications.

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Working Groups

Still Image Working Group
This group is involved in a cooperative effort to develop common digitization guidelines for still image materials.

Audio-Visual Working Group
The goal for this working group is to identify, establish, and disseminate information about standards and practices for the digital reformatting of audio-visual materials by federal agencies.

Last Updated: 11/07/2016