NCJ Number
200466
Journal
Journal of Forensic Sciences Volume: 48 Issue: 3 Dated: May 2003 Pages: 593-603
Date Published
May 2003
Length
11 pages
Annotation
This paper discusses the application of a background correction technique to photographic images to provide increased discrimination, using bloodstain evidence as an example.
Abstract
In photographing crime scenes and forensic evidence, there are some circumstances in which either variable lighting of the surface of interest or patterning of the surface on which the evidence sits can produce a relatively poor view of the evidence in a given photograph. These problems can be reduced or eliminated by performing background corrections on photographic images. The authors first explain the theory of the background correction method in a quantitative manner for transmission mode photography; the theory is then extended to approximate treatments of "normal" (reflectance) photography. The treatment is based on the use of a consumer digital camera that can provide linear images and that has controllable variable shutter speeds. The camera used in the work described in this paper was a Canon D-30 digital single lens reflex, with either a Canon 24-85 mm zoom lens or a Canon EF 100 mm F2.8 mm macro USM lens attached. The case examples described in this paper involved the enhancement of photographic images of bloodstains on problematic materials, i.e., a dark red rumpled shirt with a glossy finish, dark blue stretch jeans, and black jeans with blood and dirt. The production of background corrections through three wavelength linear images provided the best detectability of blood in the photographic images. The entire process is based on the mathematical treatment of the whole image consistent with standard analyses of absorbance or reflectance. 9 figures and 21 references