Anti-print Scan Digital Watermark Algorithm

For a long time,printed matter has been widely used in production and life as a common information exchange tool.However,it is extremely easy to be copied or even tampered by lawbreaker,which has brought great damage to the security of social intellectual property rights and production innovation.Traditional digital watermarking technology is a major measure to protect information security,but its application range is limited,and it cannot effectively deal with printing and scanning attacks.At the same time,it also has the defects of transparency and low embedding capacity.How to develop a watermarking algorithm that can resist printing and scanning attacks has become a hot topic in social research.At present,transform domain algorithms can effectively solve this situation.Among them,the LL component after DWT transformation has better robustness,and the DCT intermediate frequency coefficient can compress image energy well while reducing the correlation between image pixels.SVD algorithm has stability and rotation invariance.However,how to combine the advantages of these three algorithms and increase the watermarking capacity is also a major problem for research.This paper explores the influence of the watermark scrambling period on the robustness and transparency of the algorithm.At the same time,it combines the invariants of the images before and after printing and scanning,and designed three new digital watermarks that can resist printing and scanning algorithm,they are the improved DWT-SVD binary watermarking algorithm,the improved DWT-DCT binary watermarking algorithm and the optimized DWT-DCT gray watermarking algorithm.Firstly,the binary watermark and the gray-level layered watermark were preprocessed and encrypted respectively,and the probability distance and gray value variance scrambling were jointly evaluated for the two watermarks after processing,and the best scrambling period is obtained.Algorithm 1 firstly performed SVD processing on the scrambled watermark,and embedded the S component into the low-frequency region of the carrier image after 3DWT transformation.The PSNR after embedding the watermark was 51.5680dB.Algorithm 1 and 2 summarized the characteristics of the images before and after printing and scanning,and determine that the intermediate frequency coefficients after DWT-DCT transformation tend to be similar.First,2DWT transformation was performed on the carrier,and then 8x8 block DCT was performed on the LL to obtain 4 sets of intermediate frequencies coefficient.Algorithm 2 selected a group of intermediate frequency coefficients with the highest peak signal-to-noise ratio as the embedding position of the scrambled watermark.Algorithm 3 divided the gray-scale watermark into 8 bit planes,scrambled the high 4 bit planes,and embedded the scrambled high 4 bit planes into these 4 sets of intermediate frequency coefficients in turn.Experiments had proved that in the case of various attacks and print scanning attacks,the NC of the watermark extracted by these two algorithms is about 0.9,which had strong anti-attack ability.At the same time,this paper developed a digital watermarking system based on MATLAB for Algorithm 3,which can realize the reading of carrier and watermark,preprocess of gray-scale watermark,embedding and extraction.