In forensic science, striation marks form a large and important portion of relevant cues. They comprise the groove patterns on the circumferential surface of bullets, where the individual characteristics of the barrel-production marks as well as damages due to usual wear-are concentrated in strictly straight grooves. Moreover, many tools produce groove-shaped marks when used in a dragging movement. To suppress irrelevant regions without grooves and consequently improve an automated comparison system, a segmentation of the actual groove area on the specimen is useful.
In this contribution, an image processing method is presented that uses an illumination series to robustly segment striation patterns from mainly isotropic background areas. The illumination series is obtained with a spot illumination whose azimuth is varied systematically. The strategy is based on the modeled characteristics of local contrast with respect to the azimuth of the illumination: Whereas pronounced maxima of the local contrast can be observed when the striae are illuminated perpendicularly, an isotropic background texture shows less distinct maxima for random azimuth angles. The qualification of the approach is demonstrated on the segmentation of faint tool marks. Experimental results show that the methodology ensures the correct segmentation of such marks.