Combination Of The Human Visual System In The Wavelet Domain Image Watermarking Algorithm

This dissertation studied technique of image digital watermarking based on wavelet transform. The purpose of the research, the history of the watermarking technique, the development status of multimedia watermarking and the characteristics and classification of watermarking were reviewed. This dissertation surveys systematically, the basic frame of the watermarking system and attacks classification and typical algorithms. Then, this dissertation introduces the basic knowledge of wavelet transformation including the background of wavelet analyzing, consecutive wavelet transformation, discrete wavelet transformation, and multi-differentiating analyzing and Mallat algorithm. On this basis, several image digital watermarking algorithms based on wavelet transform were presented.This dissertation introduced a wavelet watermarking method based on human visual system (HVS). In the algorithm, using the HVS to compute the JND threshold in wavelet domain of original image, the watermark information were embedded into a set of wavelet coefficients of lager JND threshold. The experiments showed that this algorithm had strong robustness and invisibility. As the embedding intension of each wavelet coefficient was the same, the strong resistance to watermark attacks of this algorithm wad based on watermark transparency damaged, If the watermark was too large, such damage was more evident. Therefore, the algorithm was adapted to small-capacity watermarking system.This dissertation studied the image watermarking capacity analysis in wavelet domain. First, the watermark embedding model was determined, which was achieved by the rule of modifying the wavelet coefficients, the watermark embedding intension was calculated by JND model. Then, the estimation of watermarking capacity were established by the watermarking capacity formula in this watermark embedding model; By the watermark attack type and intensity, watermarking capacity estimates of original image could calculate. Algorithm could adjust to the size of watermark by the estimate. Generally, as the type and intensity of watermark attacks could not be determined, a group of wavelet coefficients with lager allowable distortion was chosen to embedded watermark based on the watermarking capacity analysis, the watermark embedding intension was decided by allowable distortion. Experimental results showed that this algorithm could get a watermarked image with perceptual invisibility. Moreover, the algorithm was robust to typical watermark attacks such as: noise adding, image filter and JPEG compression. As the algorithm used chaotic system to pre-process watermark, algorithm had high security and robustness to cropping attack. Whereas, the effect of watermark extraction by this algorithm under others geometric attacks were not perfect.A geometric attack resistant image digital watermarking algorithm based on wavelet transform was proposed in this dissertation. First, several typical geometric attack resistant watermarking scheme were introduced. This algorithm regarded the low-frequency subband of original image as the image character to embed watermark. The low-frequency subband was divided into many blocks, and then 1 bit of watermark information was embedded into each block repeatedly by quantization, and according to the characteristics of human visual system, we increased the quantization step of wavelet coefficients in highly textured areas. For watermark extracting, the 1 bit of watermark information was obtained by majority rule from each block. The watermark capacity of the algorithm was large and we didn't need the original image to extract watermark. Experimental results showed that the algorithm could effectively resist geometric attacks in various ways, and it also strongly robusted against the common attacks such as noise adding and JPEG compression etc.