CHOOSING A DELIVERY METHOD FOR DIGITAL COLLECTIONS
The choice of a delivery method for your digital objects should include a review of several options. Choose an option that meets your goals, budget and access needs. Choose a delivery method that meets the needs of your audience. Access to your digital files should be user driven and should conform to the goals of your organization. Each delivery method will require a plan for maintaining the file and format. Thought should also be given for creating a master file of digital objects that can easily be migrated with new delivery options in the future.
Access interface:
World Wide Web
The internet has become the delivery method of choice for most organizations
that plan a digital imaging project. The attraction of universal access
for all is hard to resist. The ability to display images and text documents
online for access is often the motivation for embarking on a digital project.
However, digital objects are really just pictures of a photograph, map
or text page. In order to create retrievable text that provides a description
of the information in the picture, either indexed metadata or OCR text
has to be stored with the picture.
When choosing to deliver digital images using a web site, the project
will need to develop competency in a second set of technology, web development
and design. If the skills and equipment to create web delivery are already
in place in the organization then posting digital images to a web site
is a good outcome for the project.
While the Internet has many strengths, it may exclude access by those without Internet availability. However, with the use of public library equipment, the patron can access the files during a library visit as they do for printed material. Most of the recently digitized images targeted for public access are displayed over the Internet.
Most personal computers display images in 100 dots per inch (dpi) or less, with 72 dpi being a common standard. A quality of display in excess of 200 dpi is often lost on present monitors. If the object is scanned at higher resolution, it won't be displayed in its entirety on a monitor screen. It must be either divided into sections or 'panned' from top to bottom and side to side. One use of a higher resolution image is to support 'Zoom' function. For example, to see greater detail of an image, the observer can mark an area of an image and select Zoom. If a higher resolution image is available, it is displayed for the marked area.
Servers
Computer equipment is needed for the storage of digitized objects and
their discovery and display. For Internet delivery, a Web server is required.
This server should be powerful enough to handle large image files as well
as their index database. Desktop PC based Internet servers are not recommended.
At minimum a server using the NT, UNIX, LINUX, AIX or comparable operating
system is required. Typical prices for such a device in 2002 ranged from
$5,000 to $15,000.
Internet Access
Connection to an Internet Service Provider (ISP) is required. For Web
server use, ISPs typically charge from $100 to $500 per month for fractional
T1 line access. Based on the bandwidth load, more of a T1 capacity may
be needed, therefore increasing monthly charges.
Storage
Image files place high volume demands upon file storage. When a patron
selects a particular image file from its metadata index, the transfer
of the image to the patron's screen should be fast enough to meet their
expectations. More than ten seconds of download to a client machine for
viewing frustrates recreational viewing.
To achieve fast delivery speeds, the image files must be stored on drives that are optimized for transfer. Arrays of CD drives are acceptable for small collections. Use of optical drives and "jukeboxes" are recommended for larger collections (more than 10 CDs worth).
CDs
The inclusion of CDs as output medium allows for commercial distribution.
When a runtime indexed search engine/viewer program is added to each CD,
the patron can avoid the need for extra software. It also is a durable
medium for server jukebox file systems. (http://www.library.cornell.edu/preservation/kodak/cover.htm)
Microfilm
Microforms (roll and fiche) have an important place in preserving documents
and images. While electronic file formats are expected to evolve, making
obsolete today's formats, re-scanning from microforms appear to provide
a durable replication for the next several decades, if not centuries.
The present high degree of resolution of microforms support a "film-first",
then scanning from film approach. A drawback to consider is the scarcity
and cost of color microforms. The predominant option is black and white
reproduction. Maps and large artwork are extremely difficult to capture
on microforms. Also, fragile originals must be handled manually, thereby
increasing the time and risk to capture their information.
35
mm Slides
A variation on microform capture is the use of photographic copies. This
is the preferred medium for capturing images of physical artifacts. The
slides are then scanned. 35 mm Slides may not satisfy archival needs.
TOP
Options to Consider
- Digital objects captured for delivery over the web should be stored in a database where the images and documents can be matched to searchable content presented in metadata fields or other text descriptions.
- Before developing
a web design visit, many sites to learn what style of presentation you
like best. Provide several examples to your web designer.
- Consider using CDs as a delivery method. This works well when the organization does not have the capacity to create or maintain an integrated web site.
- Images and finding aids can be created using local resources and the output can be contracted out to a vendor that specializes in creating searchable CDs.
- The project goals and anticipated use of the digital files will guide your choice of delivery method.
- Your user profile will determine the delivery methods and file formats.
- Do you have administrative and content metadata sufficient to support access?
- What is the life expectancy of the digital files?
- What will be your method to migrate master files to new platforms?
- What will be your storage approach?
- Will you need to reproduce images for sale or use by others?
- Will the collection grow? Can it be enhanced or easily weeded?
- Are you using standards to assure interoperability?
- Do you have or can you get permission to publish the digital objects on the web?
- Have you addressed all the copyright issues before publishing on the web?
