This study determined whether the Polynomial Texture Mapping (PTM) technique improves photographic images of forensic impression evidence (shoes and tires); it also developed a portable PTM unit that can be used in the field.
PTM software was developed by Tom Malzbender of Hewlett Packard Laboratories for the purpose of improving the photorealism of texture maps. This software is able to map light values from digital images taken with multiple light sources, creating a light space model in a single image. The light direction in this image can be changed in real time, allowing unlimited variation of the light angle within the hemisphere of the photographs. Overall, the research found that the use of PTM technology for the documentation and evaluation of impression evidence improves the quality of the analysis, and it is faster in capturing different oblique-lighted images of an impression compared to single-image oblique lighting and casting with dental stone. Although many of the areas of unique detail in footwear and tire impressions that improve with the PTM technique were visible in the traditional photographs, the shape of the detail was not as well defined; however, the use of the PTM technique did not improve the visualization of texture in all of the impressions captured when compared to traditional photography techniques. Additional research could include an even smaller unit for use in latent print and questioned-document examinations. The Laboratory PTM dome at Hewlett Packard Laboratories is approximately 3 feet in diameter and contains 50 fixed lights or strobes. The portable unit developed requires more human intervention than the PTM dome. Also, there is a potential weakness in capturing images with the portable unit during daylight hours. This can be overcome, however, by using any opaque material for shading the impression. 22 exhibits and 11 references