Faxed document image restoration using gray level representation

The paper describes an image restoration algorithm for degraded faxed images, for example, salt and pepper noise and the partial omission of figures. Removing these types of degradation is paramount to achieving high performance fax OCR systems. Some observations that enable effective restoration of fax degradation are: (I) the contour shapes of figures may be preserved microscopically; (II) degradation characteristics can be estimated by utilizing the distribution of neighboring pixel values; and (III) the ununiformity of sensor sensitivity causes similar degradation in vertical bands. The proposed method based on these observations comprises the following steps: producing gray level images, restoration based on local pixel distribution, and restoration based on vertical specification. The experimental results based on actual faxed documents show the effectiveness of the method.