Techniques for the segmentation of striation patterns

In this contribution, image processing techniques are investigated to robustly segment faint striation patterns from mainly isotropic background areas. Whereas well-known procedures to determine local anisotropy can be applied directly to single images, this paper describes an alternative strategy that uses an illumination series. The series is obtained with a spot illumination whose azimuth is varied systematically. The technique is based on the characteristics of the 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 in forensic science. Experimental results show that the methodology ensures the correct segmentation of such marks.