NCJ Number
225527
Journal
Journal of Forensic Identification Volume: 58 Issue: 6 Dated: November/December 2008 Pages: 647-659
Date Published
November 2008
Length
13 pages
Annotation
This article presents a step-by-step tutorial for creating and using high dynamic range (HDR) images in a forensic application.
Abstract
In the testing procedure described, HDR images of fingerprints on various materials consistently produced ridge detail of greater clarity and contrast than a normally exposed photograph. Standard digital processing techniques were not sufficient to compensate for the disparity between the standard photographs and the HDR photographs in most cases. Instead, the processing techniques usually widened the gap between the photographs. Although taking several photographs at different exposures and merging them together is more time consuming than taking a normal digital photo, it could provide the examiner the extra detail needed to identify a difficult latent print. Starting with the highest quality image possible prior to further adjustments in Photoshop provides the examiner more information with which to work and produces a better final image. An HDR image is a fusion of photographs of the same scene, in the current case a fingerprint, taken with different amounts of exposure. By using this procedure, the photographer is able to record a larger range or fidelity of luminance values in the fingerprint image. Normally, an algorithm is used to construct the HDR image. Photoshop CS2 and CS3 are now capable of doing all of the reconstructing. A fingerprint examiner can easily select which images to merge into an HDR image without dealing with confusing algorithms. This procedure is described for photographing fingerprints on a black and white book cover (glossy finish) treated with gray magnetic powder, a soda can treated with black magnetic powder, a piece of pink paper treated with ninhydrin, and a piece of green paper treated with ninhydrin, as well as a patent print on the adhesive side of a piece of brown packing tape. 6 figures and 1 reference