Managing Images

Having spent considerable time, effort and money producing often thousands of images it is of the utmost importance that the images are correctly stored and cared for. Like any asset, digital images can be misplaced, damaged or simply inaccessible because of hardware or software obsolescence.  The quantity of data produced by typical small museum imaging projects means that management of the images becomes an important consideration for both current activities and future planning. As such, planning for digital imaging projects should ideally include a policy for managing the assets once they have been created.

The image capture process will create master images which ideally should be stored on archival format devices with at least one copy stored off-line or semi-online mode. Normally one or more surrogate images will be created from the master images for output purposes such as Web display. The management of the master and surrogate images will require careful planning to ensure that proper access is maintained. This information can be recorded in an image catalogue or database linked to or integrated with the existing collections management database.

To ensure there are no confusing mix-ups between surrogates and master images, image-naming guidelines should be developed to record and keep track of images. For example you should consider developing a prefix or suffix descriptor to identify each surrogate image e.g. car-P1037-Sur.JPEG The Sur identifies the image as a surrogate and the object registration number tells us exactly what the picture is. It is also a good idea to include a single word identifier like car, painting, jacket etc. If you happened to misplace your car image this would then save you from having to open all your image files.

Master images

The image capture process is resource intensive. Storage requirements at this stage of the creation process are likely to be very high, depending on the number of images involved, in terms of both hard-disk/server space for work in progress and back-up local archive media, whether on local, networked or portable media. Following a review and recording process, the master images will normally be transferred periodically to a long-term archival format such as an optical medium or tape. If local archive copies of primary acquisition or master/archival files on portable media are maintained, it is essential to store them under the right conditions, identify them properly and have a strategy in place for their long-term survival.

Surrogate images

Surrogate images are subsequently created from the master images for a variety of purposes. Images used for visual references in a Collection Management database or the World Wide Web, require a low-resolution display format such as 500 x 500 pixels. An even lower image resolution of 150 x 150 pixels may also be required for thumbnail access. Digital images used for high-quality printing will require a substantially higher resolution. An 8"x10" hard copy printed at 300 dpi will require an image file with a resolution of 2400 x 3000 pixels, enhanced for high-quality printing. Each type of surrogate image may require different image editing and enhancement processes.

Less storage is required for surrogate images than for master images. Online and networked access to these images will probably be an important requirement. The image capture phase is when you should also be producing your surrogate images, consequently you need to factor in additional time and storage space.

Backup copies

An often neglected aspect of any image management and storage planning process is the provision for backup copies of both master and surrogate images. As with any situation, disasters can happen, from the destruction of the entire digital storage area to much smaller problems such as read errors on a CD-ROM. Backup procedures for surrogate images will likely be in place if these reside on a file server accessible through the network. However, master images stored on an archival format, such as CDROM or tape, should be backed up to create a second copy which should be stored separately from the originals. The backup format can be the same as the original or another format.

Storage devices & media

Planning for the storage devices and storage media must be an integral part of any digitisation project owing to the relatively high storage requirements for digital images. For even an image project of 1,000 objects with an average file size of master image of 30 Megabytes (MB) each, it is clear that considerable storage facilities will be required.

The storage devices selected for the digitisation project may be a combination of different types and formats depending on the uses and access methods required. Other storage devices can be added during the project as volumes warrant.

Types of storage media

See further information on how to evaluate media as well as information on data preservation.

Quality control

Throughout the process of digitisation it is essential that from time to time you check processes, documentation and product quality to ensure that technical, or record management errors or oversights, are picked up early and not replicated across the project. A common problem, not often picked up until the end of a project particularly if an external contractor is being used, is the resolution at which images are being scanned and stored. A check, early on and regularly thereafter, could save considerable time as well as money. Here again the need for clear and documented instructions is particularly important for external contractors.

Do you understand:

• The difference between master and surrogate images?
• The importance of making back-up copies of master and surrogate images?
• The importance of using a naming convention to identify your image files?
• Which kind of storage device will be most suitable for storing your digital images?