Virtual unrolling technology based on terahertz computed tomography

Due to the shape diversity and the occlusion problem, non-invasive inspection of cultural relic with special-shaped structures has always been the bottleneck of the existing imaging technology. We propose a virtual unrolling technique that can extract content from structures similar to folded paper and scroll, exploiting the three-dimensional imaging capability provided by terahertz computed tomography (THz CT). The method performs THz CT imaging on the object and obtains several slice images of its cross section. Considering the morphological properties of the slice image, the cross-sectional profile of the object is obtained by an improved single-pixel ridgeline extraction algorithm after suppressing the severe metal artifact on the slice images with our segmentation and inpainting-based scheme. And then a match-graft approach based on dynamic exemplar (MGDE) is developed to stitch lines of different layers into the final image. To illustrate, the occluding text content is successfully extracted from a mimic oil painting scroll samples with a thickness of sub-wavelength level. The method makes it possible for THz non-destructive inspection of similar structure that widely exist in industry, security, and especially heritage conservation.