International Congress on Archives 2004 pres 180 METCALFE C USA GSU 01 E Page 5
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International Congress on Archives
The Genealogical Society of Utah
www.wien2004.ica.org
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$75,000. The scanning equipment generally will need to be connected to a computer system. This computer
equipment must be able to handle the large amounts of data that will flow from the scanner. Slower computer
equipment will mean slower production time. Computer disk storage space for the digital files must also be
considered. Average uncompressed TIFF 8-bit grayscale files scanned at 300 DPI on the document can result in
file sizes from 20 40 MB in size. For a 35 mm roll of film with 1000 images that can translate to 20 40 GB
of disc storage space.
Purchasing microfilm-scanning equipment can be an expensive proposition. For those archives with smaller
collections a less expensive alternative exists. Service bureaus from around the world can provide the service of
scanning and converting microfilm into digital images. These service providers can provide images on a single
roll of microfilm or thousands of rolls of microfilm. Some providers will require the microfilm be sent to their
site for scanning. Other providers at an increased cost may come to the archives to scan the microfilm on site.
The service bureau alternative can allow an archive to scale their costs as they begin the conversion to digital
imaging. As the archive gains experience with the digital imaging, decisions can be made to continue vendor
provided scanning or to acquire equipment and train archives staff to do the conversion.
Maintaining a facility that images documents on microfilm and stores the microfilm in an archival manner
requires trained personnel that understand the archival process. Capturing and preserving digital images requires
specialized knowledge. However, this knowledge is no more complex than the knowledge required for
microfilm imaging and preservation. Dedication to training personnel in the digital process will allow for wise
decisions in establishing a digital program. Mentoring by established archives or institutions can assist in
gathering this knowledge and training personnel. The GSU and other institutions can provide knowledge about
the general processes and assist in establishing a digital program.
If the archive decides to establish its own in-house microfilm conversion or digital imaging program, dedicated
personnel will most likely be necessary to run and maintain the equipment, process images, establish
preservation and migration plans and implement them. If the archives only desires to house digital images, then
personnel already assigned to preserve other objects may be trained to plan and implement a digital preservation
and migration plan.
Choosing a proper file format for the digital images can be an important decision. Microfilm can be scanned to
digital files of varying file formats. Most primary scanned images are in bit mapped or raster graphics file
format. These images are composed of rows and columns of dots or pixels that represent the scanned image. The
number of rows or columns per inch of document represents the dots per inch or DPI resolution of the image. As
the DPI increase so does the file size of the document increase. A 300 DPI resolution document will be two to
three times as large as a 200 resolution DPI document.
Images can be stored in compressed or uncompressed file formats. Compressed formats squeeze the file size
down and allow for more images to be stored in the same amount of storage space. Two types of compression
are used, lossless and lossy compression. Lossless compression allows the image to be restored to its original
size and quality without loss of information or degradation to the file. The other version of compression is lossy
compression. This compression scheme allows the image to be reduced to very small sizes relative to the
original file size. The compromise is that quality of the image is sacrificed. Once compressed the quality of the
original image cannot be returned after decompression. This compression scheme is used with the JPEG image
format. The amount of compression in a lossy file format generally corresponds to the quality of the image
delivered. Less lossy compressed file sizes tend to provide better quality images. Higher lossy compressed file
sizes cost less to store and can be delivered more quickly over network and Internet connections. A careful
balance of image quality, speed of delivery and cost of storage must be considered when determining the
amount of lossy compression to use on a set of digital images.
Several different image formats exist. TIFF is considered by many to be the de facto standard image file format
for digital preservation. This raster-based format can allow for uncompressed, lossless compressed and lossy
compressed images. Many institutions store preservation images in TIFF uncompressed formats. JPEG is
another common image file format. JPEG is a lossy compression format. This format can deliver readable
images at greatly reduced file size. This is one of the standard image file formats used on the Internet. Several
other public domain and proprietary file formats exist.
Careful consideration must be given to the selection of a file format. Formats should be selected that are
generally available throughout the digital imaging and computer world. Selecting a file format that is not
