Examination of Firearms Review: 2007 to 2010 - Interpol

purpose of this study. Examiners having at least some experience with footwear
impressions analysis were involved. Images were taken using a high quality (14
megapixels) digital camera and a medium quality (6 megapixels) one, a 35mm film
camera and a 120 format film camera. Digital images were taken in the “zero
compression” JPEG format. The conclusions of this study were as follows:
• Both digital cameras of 6- or 14- megapixels are satisfactory substitutes
for the 35mm film camera for most regular shoeprint cases,
• In those special cases where higher resolution is required, a 120 format
film camera is recommended,
• There is not yet a simple and suitable digital solution for life-sized prints.
Chung (12) describes a method of photographic enhancement of difficult-tocapture
two-dimensional (2D) prints by the combined effect of overhead soft box
lighting and the Tilt-Shift lens (perspective control lens) presented earlier by this
author (13). This combined method was tested on different types of impressions,
on different substrates, and was found to be superior over traditional photographic
methods.
Brown and et al (14) examined the forensic application of high dynamic-range
(HDR) photography. These authors used Photoshop CS4 and Photomatrix Pro 3
software for combining several (3 – 5) images taken in different exposures,
resulting in high-quality 32-bit images. One of the examples presented in this
article was of a shoeprint. Combining multiple exposures of a 3-dimentional (3D)
shoeprint into a single HDR image allows observing a detailed print. This method
is also useful for capturing prints on a multicolor background (like wallpaper,
magazine cover, etc.)
The 2010 HOSDB newsletter mentioned above (10) contains, among other useful
and practical information, a best practice guide for the imaging of footwear marks,
including recommendations for optimum imaging techniques for various types of
marks and surfaces.
Buck and her colleagues (15) used a high resolution 3D optical scanner for
recording footwear impressions and tire tracks in snow. Their results proved that
non-destructive 3D optical surface scanning is a suitable method for the
documentation of impressions in snow. The 3D models of the scanned
impressions in snow displayed a high accuracy including all the fine details.
Casting footwear impressions in snow has always been a difficult assignment for
forensic identification specialists, and the 3D optical surface scanning is
apparently an accurate and efficient new method for documenting impressions in
snow without contact. Effective results can be achieved even in different kinds of
snow and under various meteorological conditions. The method is also suitable for
impressions in soil, sand or other materials
Polynomial Texture Maps (PTMs) are a simple representation for images of
functions instead of just images of color values. In a conventional image, each
pixel contains static red, green or blue values. In a PTM, each pixel contains a
simple function that specifies the red, green or blue values of that pixel as a
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