Multipurpose watermarking scheme using essentially non-oscillatory point-value decomposition

Abstract

In this paper, a multipurpose watermarking scheme is proposed. The meaning of the word multipurpose is to make the proposed scheme as single watermarking scheme (SWS) or multiple watermarking scheme (MWS) according to our requirement and convenience. We first segment the host image into blocks by means of Hilbert space filling curve and based on amount of DCT energy in the blocks, the threshold values are selected which make proposed scheme multipurpose. For embedding of <i>n</i> watermarks (<i>n</i> - 1) thresholds are selected. If the amount of DCT energy of the block is less than the threshold value then ENOPV decomposition is performed and watermark is embedded in either low or high or all frequency sub-bands by modifying the singular values. If the amount of DCT energy of the block is greater than the threshold value then embedding is done by modifying the singular values. This process of embedding through ENOPV-SVD and SVD is applied alternatively to all (<i>n</i> - 1) threshold values. Finally, modified blocks are mapped back to their original positions using inverse Hilbert space filling curve to get the watermarked image. A reliable extraction process is developed for extracting all watermarks from attacked image. Experiments are done on different standard gray scale images and robustness is carried out by a variety of attacks.