MULTI-SCALE SEMI-TRANSPARENT BLOTCH REMOVAL ON ARCHIVED PHOTOGRAPHS USING BAYESIAN MATTING TECHNIQUES AND VISIBILITY LAWS

ABSTRACT This paper presents an automatic technique to remove semitransparent blotches (due to moisture) from archived photographs and documents. Blotches are processed in the HSV space. While chroma components are processed using a simple texture synthesis method, the intensity component is split into an over-complete wavelet representation. In the approximation band, the blotch is modelled as an alpha matte which reduces the intensity of the image in a non-uniform yet smooth manner. The alpha matte is estimated using a Bayesian approach and its effect reversed. Wavelet details are left unchanged in the case of perfect semi-transparency or attenuated using visibility laws whenever dirt and dust cause spurious edges. Experimental results achieved on many historical photographs show the effectiveness of the proposed approach