Reduction of Bleed-through in Scanned Manuscript Documents

Many old manuscript documents were written on both sides of the paper, and the bleed-through from one side of the document to the other increases the difficulty in reading or deciphering the information on the page. This paper presents techniques for reducing such bleed-through distortion using techniques of digital image processing. Both sides of the document are scanned, maintaining full spatial and amplitude resolution (8 bits/sample). The bleedthrough is reduced by processing both sides of the document simultaneously. First the verso side is flipped from left to right, and then the recto and flipped verso images are registered. This registration is necessary since it is impossible to perfectly align the front and back when scanning the document, and the scanner may not be perfectly uniform. We used a six-parameter affine transformation to register the two sides, determining the parameters using an optimization method. Once the two sides have been registered, areas consisting primarily of bleed-through are identified and replaced by the background color or intensity. The method has been tested on a number of documents, including documents we generated under controlled conditions and some original manuscripts; the readability of documents with heavy bleed-through has been greatly improved by this method.