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last updated:
October 7, 2014 2:55 PM

J. Trant. "Framing the Picture: Standards for Imaging Systems", ICHIM/MCN, San Diego, CA, Oct. 1995.


4. Image Documentation

Documenting digital images which depict works of cultural heritage requires recording information both about the work, and about the digital representation of the work. If the digital image was created by scanning an existing photographic reproduction, the characteristics of that reproduction will have an impact on the resulting quality of the digital image, and should be documented as well. The same is true if an image was derived or subsampled from another digital image file.

Describing Content

The cultural heritage community has as history of collaboration centered on the question of content description. Data structure guidelines or standards published in recent years include Spectrum, The Documentation Standard for the United Kingdom,51 Categories for the Description of Works of Art, the report of the Art Information Task Force,52 and International Guidelines for Museum Object Information: The CIDOC Information Categories.53 Available data value standards include the Art and Architecture Thesaurus (AAT)54 and the Union List of Artists Names. The Canadian Heritage Information Network as recently published Data Content Standards: A Directory.55 This document lists standards, standards organizations and standards development projects, categorizing them by discipline, and by scope. Content documentation standards for imaging systems should conform to those of the relevant subject discipline.

Describing Surrogate Images

The manner in which a work of art or artifact is depicted in a surrogate image can greatly affect the utility of that image. The Data Standards Committee of the Visual Resources Association has drafted "Data Standards for Visual Resources." Although much of this proposed standard relates directly to managing information about a conventional slide collection, it includes a series of Image Elements which are unique to a visual representation. These include the format of the reproduction, and a means of recording the 'vantage point' from which the image was taken.56

Describing Digital Image Files

There is as yet no consensus regarding the information required to document digital image files. We need to determine what information should always travel with an image, and therefore must be placed in the image file header, and what can be stored in an accompanying text record. We need to determine how to manage relationships between image files and the text records that describe them.

Discussions of image documentation requirements have taken place within the context of the Coalition for Networked Information, and the Consortium for the Computer Interchange of Museum Information. In the fall of 1994, a preliminary framework was presented for comment, which raised the following questions: What information should be recorded about digital image files? Where and how should image files be documented? What information must be placed in the image header, and what can be placed in an accompanying text record? How should that text record be fielded? How should the relationships between image files and their accompanying text records be managed?57

A number of general kinds of information about a digital image were identified:

  1. Information required to view the image, including type (bit-mapped, vector, video), format (such as TIFF, GIF, JFIF), compression scheme (such as JPEG, LZW, QuickTime) pixel dimensions and dynamic range, CLUT and color metric (CMYK, RGB);
  2. Information about the quality and accuracy of the image, including the source digitized, the source image type, source image identification and the institution responsible for creation of the digital image (this could be a series of recursive relationships when images are derived or scanned from other images);
  3. Information about the scanning process, including light source (full spectrum, infrared), resolution, dynamic range, type of scanner (for color correction), date of scan, the identification of the scanning personnel, a record of image manipulation, (cropping, color balancing), and the addition of digital signatures or other methods of authentication;
  4. A description of how an original is depicted in a surrogate image, including mention of perspective, position, orientation, aspect, and linking between various views of the same original, or different versions of an image (browse, high-resolution, medium resolution) derived from the same scan;
  5. A description of the work depicted, according to a known content standard, such as AACR2 or the AITF Categories for the Description of Works of Art ;
  6. Rights and Reproduction Information, documenting the copyright of the original, the surrogate image, and the digital image, and including the name of the rights-holder and possible use restrictions (on viewing, printing, or reproduction);
  7. Information about how to locate an authentic copy of the image, recorded in a form such as a Universal Resource Name/Number or Universal Resource Locator.

The refinement of this preliminary schema, and the adoption of a standard description of an image file will be critical for the archival integrity of digital visual information. This will be the only way to ensure that as image files are transmitted over networks they carry enough information with them to identify their contents. As we build digital image archives, records of the circumstances of their creation will be an essential key to the future evaluation of their contents.

Data Representation

Standard means of representing the various types of image description will also be critical to their future utility. Within the bibliographic world, content documentation is recorded according to ISO 2709, and its implementation in the MARC format. Within the cultural heritage community, progress has been made in implementing the Standard Generalized Markup Language (ISO 8879) by the Consortium for the Computer Interchange of Museum Information (CIMI). However, we are still some way from standard Document Type Definitions for museum information, as there are for books, articles and serials.58

Next Section: 5. Image Use

Informatics: The interdisciplinary study of information content, representation, technology and applications,
and the methods and strategies by which information is used in organizations, networks, cultures and societies.