Abstract

Perspective distortion always occurs while scanning thick, bound documents. This distortion mainly causes two sources of degradation for the scanned grayscale image -- i) shadow along the `spine' of the book, and ii) warp of the words in the shadow. In this paper, we propose a restoration system to solve these two problems. Our system first produces a vertical projection profile to detect which side of the image the shadow lies on, and a runlength method is used to find the boundary between the shadow and the clean area. We then apply a modified Niblack's method to remove the shadow. We use a connected component analysis to adjust the location and orientation of the warped word in the shadow area, i.e. the words within the boundary detected earlier. The implementation results are presented in this paper. Our system will be used in a text retrieval project for National Archives of Singapore.

Citations