Pictures in Print
Digital image storage on CD
The project accumulates data very quickly, especially when scanning maps. Aside from considerations of data backup, it is necessary to move data off the scanning computer regularly to avoid bottlenecks. Data is stored on writeable CDs in the original capture format (for scanned material at 600 dpi). Each CD holds 650MB; an A4 print scanned at 600 dpi 256 grayscale is between 20MB and 30MB, but it can take 3 CDs to store the parts of a large map scanned at 600 dpi 24 bit colour.
Hardware and software
An external SCSI CD writer is used (a Plextor Plexwriter) and Ahead's Nero Burning ROM software (version 5). This allows a test and burn process for the creation of each CD (which takes about 25 minutes for both stages) to ensure that the final product works.
Media
Investigation showed that no one brand of CD was recognised as of archival quality, and there was controversy about several aspects of using CDs. However, it was clear that writable CDs were preferable to re-writables, and that some brands were mentioned regularly. TDK's CD-R74 was chosen as it had been recommended on several occasions and used by other departments. As the disks were inexpensive, it was decided to cut two copies. This provides some element of fallback in the case of media failure - it is not clear how stable writable CDs are. The manufacturers claim a 100 year life for the media, but they are susceptible to scratch damage etc. so this seemed a useful safeguard. It must be stressed that the CD method is not regarded as of archival preservation quality, but rather a convenient means of medium term storage - the project did not include a long term preservation element but is primarily concerned with creating images to facilitate access. Approximately 130 CDs were used to store 1,800 images (although these varied so greatly in size as to make this statistic of little relevance). About 1 in 50 of the blank CDs used appeared to fail to work.
Useful websites on CD media
For information on recordable CDs: Andy McFadden's CD-Recordable FAQ at http://www.cdrfaq.org/
Media longevity in general: Media Sciences at http://www.mscience.com
CD storage
The CDs are stored in archival non-acidic envelopes in archive boxes in controlled conditions (a strongroom).
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Page maintained by Richard Higgins (e mail - r.i.higgins@durham.ac.uk). Last revised: May 2004