Circular Noises Removal from Scanned Document Images

Defects inspection and correction is an important topic in the fields of scanned documents preprocessing. In this paper, a very fast and robust algorithm is proposed for locating and removing a special kind of circular noises caused by scanning documents with punched holes. Firstly, original image is reduced according to an elaborately selected ratio. Punched holes after reduction will leave some distinctive small regions. By examining such small regions, holes noises can be fast detected and located. To diminish false detections, Hough transformation is applied to the roughly located regions to further confirm the located holes. Finally, circular noise is eliminated by fitting a bi-linear blending Coons surface which interpolates along the four edges of noisy region. Experiments on a variety of scanned documents with punched holes demonstrate the feasibility and efficiency of the proposed algorithm.