National Library News February 1999 Vol. 31, no. 2

Digital Imaging: Towards International Agreement on Guidance, Guidelines and Best Practices

The closing years of this decade have seen an increasing amount of digitization activity among libraries, archives, museums, and other organizations. The scope of this digitization runs the gamut from text to images, recorded sound, film, and other material of all shapes and sizes. As this work continues beyond experimental projects to larger-scale programs, many library managers and specialists are concerned about the issues of user needs, access, interoperability, preservation, effectiveness, efficiency, technological change, and a host of other topics.

A common denominator in most digitization projects is the use of digital imaging to re-format physical images so that they can be delivered to users over networks and preserved for future use. Such preservation is not trivial: the difficulties of using computer files that are only a few years old are well documented, as software, hardware, and formats continue to change.

Ensuring that digital images can be preserved for future access and use is a crucial issue for libraries and other organizations involved in digitization. There are plenty of standards for digital imaging, but which ones are most appropriate? What are the best practices? How should materials be selected, prepared, and scanned? What do we need to know about each image in order to migrate it to new formats safely?

These are some of the key questions addressed at the recent "Guidelines for Digital Imaging" conference, held at the University of Warwick, in Coventry, U.K., from September 28 to 30, 1998. The working conference, organized jointly by the British Library’s National Preservation Office (NPO) and the Research Libraries Group (RLG), was held so that participants could collaborate on working towards international agreement on guidelines and best practices for digital imaging projects. Major objectives of the conference included exchanging ideas on guidelines and best practices for digital imaging, achieving agreement on the purpose, scope, and practical implications of such projects, and learning more about current digital imaging projects.

Some 100 representatives of libraries, archives, museums, academia, and the private sector from the U.K., Ireland, continental Europe, the U.S., Australia, and Canada attended the conference.

In delivering the keynote address, Anne R. Kenney of Cornell University called on participants to work towards agreement on what is the best guidance for digital imaging projects, rather than necessarily on guidelines. She distinguished between the two by noting that while guidance encourages rational choices based on questions, guidelines tend to be prescriptive.

Experts gave presentations on issues involved in selection, preparation of materials, and image capture. Participants then joined one of three groups following these themes to determine areas of agreement on best practices, areas of significant differences of opinion, and areas where further work was needed. The convenors presented the results of the discussions in plenary sessions.

At the time of writing, the conference proceedings were still in preparation. The author takes responsibility for any over-simplifications or inaccuracies in this summary report. Readers are encouraged to view the complete proceedings at http://www.rlg.org/preserv/joint/index.html.

The convenors for the group dealing with selection of materials for digital imaging were Julia Walworth (University of London), Paul Ayris (University College, London), and Janet Gertz (Columbia University), who presented the results of the selection group’s discussions. It was recommended that:

• no single set of guidelines be prescribed;
• institutions should formulate their own selection policies and guidelines for decisions on what to digitize;
• there should be a unified site for information and guidance on the process of selection for digitization.

A number of general points were also made:

• in selection for digitization, the role of digitization in the overall institution (not just the library) should be considered;
• there is a problem in finding out what users want/need;
• selection requires a variety of expertise (content, systems, project management, digital imaging, encoding, etc.) early in the selection process;
• rights management problems must be addressed;
• overall collection needs must be considered;
• it is necessary to say "no" to proposals which do not meet institutional criteria, even when specific funding is available or can be obtained.

The group dealing with preparation of materials for digitization was convened by Alison Horsburgh (Scottish Record Office), Ann Swartzell (Harvard University), and John McIntyre (National Library of Scotland), who reported general agreement on best practices or approaches regarding:

• control of lighting conditions (controlling UV light and lux hours, not just lux levels);
• obtaining and using book cradles (on this point, it was noted that many of the best book cradles are designed by conservators working with a knowledgeable engineer, builder or technician);
• conservation considerations;
• digitization of oversize materials;
• restrictions on access to originals once they have been digitized (user access to originals should be discouraged unless there is a legitimate need to examine them);
• provision of appropriate finding aids for digitized collections;
• linking the digital resource to the original through metadata.

It was also agreed that although digitization has a preservation value, it is not a preservation action as such; nor are the resulting digital objects preservation media per se. It makes sense to convert fixed media to digital objects to provide access and support preservation, or to convert to digital formats simply to provide access. But it does not make sense to digitize for preservation as an end in itself, with no consideration of present and future access.

A legitimate divergence of viewpoints on disbinding and the use of surrogates for digitization was recognized. The questions to be considered in these cases include the purpose of the digitization (e.g., will the quality of a surrogate suffice?), the projected life span of the material (will disbinding or surrogate production shorten this?), whether items must go off-site for digitization (which may argue against use of originals), and whether the physical items are already at risk of deterioration, in which case it is extremely important to minimize handling.

In terms of areas for action, it was agreed that more research on costs is required, and that collaboration is needed to help libraries develop staff expertise (where necessary) or to find coping mechanisms and appropriate training in preparation of materials for digital imaging.

The digital image capture group noted that, among other things, agreed definitions of what is sufficient or acceptable as a "digital master", a "faithful digital reproduction", and quality control guidance are required. The latter includes distinguishing between objective and subjective quality assurance criteria, though both have value.

General agreement was reached on which file formats should be used to help ensure preservation: images should be in the TIFF format (Tag Image File Format), or in emerging "TIFF-like" formats such as PNG (Portable Network Graphics format, pronounced as "ping") and SPIFF (Still Picture Information File Format). General agreement was also reached on the following points:

• digital image compression should be lossless;
• more flexibility is needed in image file headers so that all necessary metadata can be included (e.g., documentation of the gamma levels of colour);
• preventing irretrievable loss of image information is a key issue in choosing digital image formats for preservation;
• quality control is essential. Before work begins each day, attention must be paid to such basics as scanners and monitors.

The general consensus from the plenary session was that digital images should be created using the best standards and practices possible, but with due consideration to the practicalities and the larger picture. Longer-term needs and capabilities must be kept in mind. Therefore, the initial high-quality digital image files should be retained, even when access versions are produced and they make optimum use of current capabilities such as monitor resolutions and existing Internet bandwidth.

Following the plenary presentations, Michael Day (CEDARS Project) presented a paper on metadata for preservation. He noted that all the approaches aimed at ensuring continued long-term access to digital resources depend not only on descriptive metadata — which is clearly necessary to identify and manage digital items — but also on appropriate preservation metadata. Current approaches to long-term access include migration to new standards/formats, conservation of hardware and software, and technology emulation. All these depend on the identification and collection of relevant metadata, such as the standard(s) used in creating the digital files, the practices employed, and the hardware platform, operating system, software and version used.

Margaret Hedstrom (University of Michigan) spoke on digital archiving for preservation, summarizing her preliminary survey results of 54 RLG member libraries’ current practices in digital preservation. Of these, 36 do not yet have written policies for managing digital materials. Eighteen already have at least some policies including policies on acquisitions (16) and migration (7). Many responding libraries indicated that in the next three years they plan to develop digital preservation policies (51 out of 54) and 52 plan digital conversion projects. In concluding, she spoke of the lag between the development and implementation of best practices, and the gap between current guidance on digital archiving and institutional capacities to follow through. She noted the following priorities:

• to implement the best practices which already exist;
• to provide training;
• to share successful policies, practices, and standards;
• to focus research efforts on emerging promising solutions.

The full report, co-written with Sheon Montgomery, is available on the RLG Web site at http://www.rlg.org/preserv/joint/index.html.

The conference was summed up by an international reaction panel composed of Seamus Ross (National Library of Scotland), Karen Turko (University of Toronto), and Colin Webb (National Library of Australia). In his closing address, Peter Fox (Cambridge University) emphasized the urgency of preserving original digital material. He added that his Digital Archiving Working Group will produce a non-technical guide on digital archiving in the spring of 1999.

Apart from the presentations and group or plenary discussions, participants found many valuable and congenial opportunities for sharing news and views with colleagues at breaks and mealtimes. This part of the conference went especially well, helped, no doubt, by the conducive surroundings and excellent meals served up by the University of Warwick’s Scarman House.

In short, the NPO and RLG organizers did an excellent job with the planning, organization, content and logistics of the conference, something which shone through at every turn. There were substantial areas of agreement on guidance for digital imaging, and each group identified important issues for further research and collaboration. The organizers and many of the participants are pursuing these outstanding issues and the agenda of establishing best practices for digital imaging.

¹ For a brief explanation of the TIFF and PNG formats, see: Shapiro, Kivi. "Graphics and Sound File Formats", Network Notes, no. 24, Jan. 31, 1996 (http://www.nlc-bnc.ca/pubs/netnotes/notes24.htm).