NCJ Number
227840
Date Published
March 2009
Length
92 pages
Annotation
This project developed an improved method of photographing bloodstains on dark surfaces without the use of chemical enhancement techniques, specialized film needs, or exposure manipulation of digital images
Abstract
The research confirmed the utility of crossed polar illumination in visualizing and documenting bloodstains on dark surfaces. The micrographs show that even seemingly matte surfaces like wool have a significant amount of white light reflected from them. They also show that the stain surface reflects white light as well. Crossed polar illumination eliminates this reflection from both surfaces, resulting in the two substances appearing more true to their intrinsic colors. This glare-reduction is the key element in the enhancement. The light source and polarizing filters are the essential components of this method. LEDs produce intense white light with the least heat damage to the filter in front of the sources, and RGB LED is the preferred LED technology. The difference between the performance of most polarizing filters is less drastic than that of the different LED types. In terms of the transmission curve of two crossed polarizers across the visual range, the wavelengths across which there was virtually zero transmission was more indicative of better performance than the maximum intensity of transmitted light. Even when using the worst performing illumination and polarizing filters, the bloodstains were far easier to visualize and document than with regular lighting. Substrates used were plain black cotton, leather, wool, silk, and polyester. All stains used were prepared by the project staff using fresh blood. Four types of stains were produced: contact, smear, 10 ml drop, and spatter. This report describes the setup for the camera, the camera equipment, and image analysis. 35 figures, 3 tables, and 27 references