The Research Of Image Watermarking Based On Wavelet Transform And Human Visual System

As a new technology which can protect copyright and authentication source in the open network environment, digital watermark is a new direction in the information security field. It embeds copyright information, such as figures, sequence numbers, words, image logos and so on, imperceptibly into multimedia data for tracing the distribution and usage of it. The special application of digital watermarking technique requires that the embedded watermark should be not only transparent to human observers, but also robust enough to resist to different attacks.Wavelet analysis is the newest implement for space-frequency analysis in the world at present, and it has been widely used in image processing. As the multi-resolution analysis characteristic of wavelet transform has the compatibility with the characteristic of human visual system (HVS), it is helpful to choose appropriate embedding location and strength for the watermark. Besides, the low complexity and space-frequency location peculiarity of wavelet transform are also in favor of improving the performance of watermarking algorithm. So the watermark technique based in wavelet transform domain has attracted broad attention. Combined the watermarking with wavelet transform has developed many new watermarking techniques, and the watermarking algorithm in wavelet transformation domain has become a hotspot for researching.After profound researching of current digital watermarking technology in the worldwide, taking static gray image as fundamental research object, thorough research has been conducted to the digital watermarking algorithms in wavelet domain. Combined with the human visual system (HVS) characteristic, two watermarking algorithms in wavelet domain are proposed as below:1,The concept of wavelet contrast is introduced into image watermarking to carry out adaptively embedding. After texture blocks classifying of the host image, the coefficient with big wavelet contrast was selected for embedding watermark. Strength of embedding depends on both the texture class which the block belongs to and the wavelet contrast of it. Experimental results indicate that the watermark is imperceptible and is robust enough to common attacks.2,Combining the fuzzy clustering with the characteristic of HVS, a fragile image watermarking algorithm in the wavelet transform domain was proposed. The low-frequency background and high-frequency textures in each block of the host image were used as a feature vector. By the way of fuzzy clustering, the characteristics of the image wereanalyzed, and thus three clustering centers with different masking effect were outputted. For each block, the embedding strength of the watermark was determined by the distances between the clustering centers and the feature vector. Finally, by modifying the SVD (Singular Value Decomposition) of the wavelet coefficient, a binary image as watermark was embedded into the host image. Experimental result proves the imperceptibility and the resistance to JPEG attack of this fragile watermarking scheme, and it is also sensitive to malicious attacks.