Research Of Blind Digital Watermark Algorithm In Image Based On Chaotic Encryption And HVS Theory

With the growth of multimedia technology and digital network communication,the research of digital information security as well as multimedia copyrightprotection becomes an important issue. As a branch of information hidden, Digitalwatermark technology is an effective mean to resolve the issue of multimedia datacopyright protection.In this paper, digital image blind watermark algorithm based on chaosencryption and HVS theory is in depth study. The watermark embedding andextraction model is established, then the parts of the algorithm of model is intheoretical study. Simulation of the experiment realize the binary image embeddingand extraction. In order to test the feasibility of algorithm, watermark attackedextraction is simulated. Based on the analysis of simulation results, the furtherimproved algorithm is proposed. Compared to previous algorithm, the improvementhas stronger robustness. Finally, these theories is applied to the embedding andextraction of the gray image watermark.According to the traditional watermark technology, scrambling transformationis done before embedding in order to eliminate the spatial correlation among pixels.But the transformation usually has periodicity, the watermark can be restored bycertain iterative times. Based on these considerations, encryption is done beforescrambling transformation in order to enhance the security of watermark. In thispaper, Spatial-temporal chaotic sequence having the characteristic of initial valuesensitivity is used to encrypt. The binary chaotic sequence is generated by OCMLmodel and improved signal function method. Then sequence randomicity isapproved by experiment. The security of watermark can be enhanced by usingchaotic sequence for encryptionThe binary image and gray image are embedded into color image in this paper,the technology of embedding and extraction is adopted as follows:(1) The original color image is transformed into the YIQ color space,watermark is embedded into the Y luminance component of the YIQ.(2) The carrier image is transformed from space field to frequency field bylifting wavelet transform, the watermark is embedded into the wavelet domain.Comparing with the traditional wavelet transform, the lifting wavelet transform has many excellent characteristics, such as simple structure, lower calculation, inversetransform can be inversely realized directly, reversible integer to integer transform,save the memory space and calculation time.(3) The watermark is embedded into the color image using ditheringmodulation algorithm based on quantization. The main idea of algorithm is that thedifferent gray value of carrier image is quantized to the median of correspondingarea according to various quantization algorithms in different quantization condition.The method does not require the original carrier image to extract watermark, it is ablind watermark technique.(4) The HVS theory is applied to this paper in order to select quantization stepadaptively. The carrier image is analyzed according to the characteristic of HVS andmasking effect first, then select small quantization step to the smoothness and lowluminance field, the big quantization step to the texture and high luminance field.Using this theory, the watermark is embedded into the color image throughMATLAB simulative environment. In order to validate the robustness, add manyattacks to watermark image then extract watermark from the attacked image. Theresults show that the algorithm can withstand noise attack, zoom attack and daubingattack especial to the JPEG compress attack, but the ability of resisting circumrotateattack is lower, the robustness of filter attack, cut attack, luminance and contrastchange attack is not higher.Owing to the shortage existing in the algorithm, the improved algorithm isproposed, error-correcting codes theory is added to the former algorithm, this paperadopt hamming code, code before embedding, decode after extracting, the error bitscan be rectified in a certain using this theory, improve the robustness of thealgorithm.The binary image watermark has little information, in order to embed muchinformation, the paper study gray image watermark algorithm based on the binaryimage watermark. Decompose the gray image into many bit planes, the higher bitplanes with important information are embedded into the carrier image. The resultsshow this algorithm has stronger robustness to filter attack, luminance and contrastchange attack, daubing attack especial to noise attack, zoom attack and JPEGcompress attack, but feebler robustness to cut attack and circumrotate attack.To sum up, the paper study the binary image watermark technique, set up theembedding model and extraction model, adopt corresponding technique accordingto the different parts of model. The watermark embedding and extraction is realized through MATLAB simulative environment. The watermark which is attackedextraction is also simulated, According to the results of experiment, the improvedmethod is proposed to improve watermark robustness. At last, the gray imagewatermark algorithm is proposed based on the binary image watermark algorithmand special technology to gray image watermark. The experiment results show thatthe algorithm proposed in this paper has stronger robustness to the noise attack,zoom attack, daubing attack especial to JPEG compress attack, but the algorithm hassome shortage, such as the ability to resist cut attack and circumrotate attack isfeebler, so the author will improve the algorithm in the future.