Abstract: Footwear prints are important evidence in criminal investigation. They represent changes in the surface morphology due to disturbance to fine particle distributions. Existing non-contact optical detection methods usually measure the light intensity contrasts between the footwear prints and the ground, which can be enhanced by grazing incident illumination. We take polarization images of footwear prints on different types of floors using a commercial single lens reflex color camera. Results show that adding linear polarizers in front of the camera lens and light source improves the contrast of footwear print images. The best contrasts are achieved in degree of linear polarization. In addition, the three-color channels of the camera can be used to examine the spectral features of the polarization images. According to the experimental results, the best contrast is obtained at the blue channel. The current work shows that grazing incidence polarized light imaging can effectively enhance the contrast of the footwear prints against the floors, which would help obtain footwear evidence in criminal investigation.

Key words: Polarization, Image enhancement, Scattering, Particle

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