This project built a digitizing device that scans impression evidence and generates a high-resolution, three-dimensional (3D) surface image and a co-registered two-dimensional (2D)color image.
The method is based on active structured lighting methods in order to extract 3D shape information of a surface. The prototype device that was built uses an assembly of two line laser lights and a high-definition video camera that is moved at a precisely controlled and constant speed along a mechanical actuator rail in order to scan the evidence. A prototype software was also developed. It implements the image processing, calibration, and surface-depth calculations. The methods developed for extracting the digitized 3D surface shape and 2D color image include a self-contained calibration method that eliminates the need for pre-calibration of the device; the use of two-colored line laser lights projected from two different angles in order to eliminate problems due to occlusions; the extraction of a high-resolution color image of the impression evidence with minimal distortion; and a super-resolution method that uses the model of the rail motion in order to further increase the resolution of the extracted color image. The digitized 2D color image has a resolution of 1900 pixels in the X-axis direction and up to 4500 pixels in the Y-axis direction. The Y-axis resolution can be increased up to 9000 pixels using super-resolution techniques. The scan of a long tire track at the lowest scan speed takes approximately 20 minutes at the slowest rail speed. Processing the resulting video to generate the 3D image and the 2D color image takes less than 1 hour on a regular PC. 60 figures and 19 references