Shape from parallel geodesics for distortion correction of digital camera document images

摘要

Distortion correction methods for digital camera document images of thick volumes or curved papers become important for camera-based document recognition technologies. In this paper we propose a novel distortion correction method for digital camera document images based on "shape from parallel geodesies." This method considers the following features: parallel lines corresponding to character strings or ruled lines of tables on extended surface become parallel geodesies on a curved paper surface and a smoothly curved paper can be modeled by a ruled surface, which is sweep surface of rulings. The projected geodesies and rulings exist in the input image derived from perspective transformation. The presented method extracts the projected geodesies, estimates the projected rulings in the input image, estimates the ruled surface that models the curved paper, and generates the corrected image, in this order. The projected rulings are estimated by the condition derived from only parallelism of geodesies without the requirements for equal spacing. This method can estimate the ruled surface model directly by numerical operations of differentiation, integration and matrix inversion without any iterative calculation. We also report on experiments that show the effectiveness of the proposed method.