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Glossary of Digital Imaging Terms

Archival Scans - In order to record the same amount of information held in a piece of film, millions of pixels are required. The slower the ISO, ASA, or film speed, the finer the grain, so the film holds more information which requires more pixels to record that information. It is not possible to record every piece of information held in the film with today's scanners. Perhaps tomorrow, scanners will hit the marketplace with such high resolutions that every hair on a person's head can be captured, but until that time, there is no such thing as an archival or preservation scan that acts as an exact replica of the original.

GIF - Graphic Image File - an image storage format that is widely used on the web.

Interpolated/Uninterpolated - Most scanners have a maximum pixel-per-inch resolution before they start guessing or interpolating the data. Interpolated files require the computer to simulate data in an image file, while uninterpolated files hold only data that is accurate to the original. Uninterpolated resolution is, therefore, preferred for accurate scanning.

JPEG - Joint Photographic Expert Group - a compression algorithm for condensing the size of image files. JPEGs are very helpful in allowing access to full-screen image files on-line because they require less storage and therefore are quicker to download into a web page.

Metadata - Data about the data. The Nebraska State Historical Society keeps metadata about every digital file created.

Permanence - In the digital world, permanence is a complicated term that requires not only the accurate refreshing of files, but the continued updating of metadata.

Pixel (per inch or ppi)- A pixel is often referred to as a dot, as in dots-per-inch, rather than pixels-per-inch. NSHS prefers to use the term pixel because it more accurately describes the digital image. In the print world, two pixels exists for every dot.

Preservation as it relates to scanning - Scanning an original photograph, document, or three dimensional object is only a method of preservation if the digital file becomes the access tool and the original is no longer available for use. We encourage high resolution scanning for all materials of extreme value in order to ensure that the information held in the original is not lost. We do not, however, intend to tout the digital file as a replacement of the original. (See Archival Scans)

Refreshment - The transfer of digital files to a new media on a regular basis. This is THE MOST IMPORTANT PART of an institution's commitment to digitization! Technology is outdated the minute it hits the marketplace. The data we generate must be retrievable five, fifty, or one hundred years from now. In order to ensure access to the data, it must be transferred to the most recent type of media storage. In one hundred years, it is very unlikely that any of the computers we have on our desks will function. We must make sure the data can be retrieved by the newest machines.

Resolution - The number of pixels-per-inch in a digital file. The more pixels-per-inch the more information held in the file, the higher the resolution.

Spatial Resolution - The number of pixels held in a file, for example 640 pixels across by 480 pixels down (640x480).

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Last updated 14 May 2001

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