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Computer Enhancement of Evidence Through Background Noise Suppression

NCJ Number
148155
Journal
Journal of Forensic Sciences Volume: 39 Issue: 2 Dated: (March 1994) Pages: 537-546
Author(s)
B E Dalyrymple; T Menzies
Date Published
1994
Length
10 pages
Annotation
Computers have been used to enhance evidence for more than 20 years and can now be used with affordable software packages to enhance images in weak or obstructed evidence through the optimization of the signal to noise ratio.
Abstract
This signal optimization is achieved largely as a result of two factors. First, the digitization of the image gives the operator far greater control over each component of the image than is possible with a photographic (analog) image. Second, the computer has the ability to discriminate between 256 separate values of gray, from black (0) to white (255), in contrast to the approximately 32 separate values perceived by the human eye. The process does not add or create information that is not already present. In addition, the skill and experience of the analyst are directly related to the result. Specific techniques available through Imagepro software are fast Fourier transform, subtraction, predevelopment capture of background, signal filtration, signal erasure, and histogram equalization. Case examples, photographs, and 6 references (Author abstract modified)