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INTRODUCTION

The authors built a digitizing device that scans impression evidence and generates a high-resolution 3-D surface image and a co-registered 2-D color image. The method uses active, structured lighting methods to extract the 3-D shape information of a surface. The prototype device uses an assembly of two line laser lights and a high-definition (HD) video camera that is moved at a precise and constant speed along a mechanical actuator rail to scan the evidence. The authors also developed prototype software for image processing, calibration and surface depth calculations. The resulting 3-D image has a resolution of 0.0438 mm in the Y-axis (along the rail motion direction), 0.2369 mm along the X-axis (limited by the HD video camera's resolution) and 0.5 mm along the Z-axis (depth). The resulting 2-D color image has a resolution of 1900 pixels in the X-axis direction and up to 4500 pixels in the Y-axis direction (depending on the speed of the rail motion and length of the scan). The Y-axis resolution can be increased to up to 9000 pixels using super-resolution techniques. The scan of a long tire track (about 1.75 m) at the slowest scan speed takes about 20 minutes, and processing the resulting video to generate the 3-D image and the 2-D color image takes less than one hour on a personal computer.