Robust Watermarking of Document and Graphics Images in Wavelet Domain

In this paper, a wavelet based watermarking scheme for the protection of document and graphics images is proposed. Document and graphics images are different from other images as such images are typically in two colors only (generally white as background and black or other color as text or drawing). In document or graphics images, white background area is usually more than the text or drawing content, therefore any attempt at watermarking, creates the problem of visual artifacts on white background. Here a spread spectrum watermarking scheme in wavelet domain is presented, which utilizes only the area covered by the text or drawing for watermarking and leaving the white background area clear of any visual artifacts. Suitable wavelet coefficients are determined for watermark embedding using a mask. Depending on the number of available wavelet coefficients for embedding, better robustness is achieved by selecting appropriate embedding strength using a simple fuzzy rule. This scheme utilizes the characteristics of human visual system by selecting high frequency wavelet coefficients of diagonal orientation. As can be seen in the computational results, clear white background area is ensured with better robustness presented on a variety of document and graphics images.