Manuscript Bleed-through Removal via Hysteresis Thresholding

Many types of degradation can render ancient manuscripts very hard to read. In bleed-through, the text from the reverse, or verso, side of a page seeps through into the front, or recto. In this paper, we propose hysteresis thresholding to greatly reduce bleed-through. Thresholding alone cannot properly separate ink and bleed-through because the ranges of intensities for the two classes overlap. Hysteresis thresholding overcomes this limitation via the two steps of thresholding and ink regrowth. In order to provide quantitative measures of the effectiveness of this approach, we constructed a novel dataset which features bleed-through and has available ground truth. We evaluated our method and a number of previously proposed approaches on ink pixel precision and recall. Hysteresis thresholding significantly improves over existing methods.