The quality of historical documents related to art and architecture, mathematics, astronomy, astrology, architecture, law, music and medicine, written around several hundreds of years, which are still available for reference today and which is preserved by libraries and universities all around the world, is poor due to physical deterioration. Digital image processing techniques are necessary to improve the legibility of the manuscripts. The deterioration processes often result in uneven background coloration across the image and the darkening of the background which reduces the contrast between the foreground text and the background color of the documents. The problem is introduced during the conversion of manuscripts to their digital image form. The proposed methodology performs the improvement in the quality of historical manuscripts having uneven background and low contrast due to the traditional mode of manufacture and the effect of ageing and degradation.