Digital Image Watermarking Technology Based On Wavalet Domain

Wavelet transformation has the characteristic of good time frequency partial, in the digital image watermarking technique domain, the wavelet domain watermark has more advantages than the watermark which based on the other frequency domain, we can nicely control the position where the watermark be imbedded and the strengths, and control the distribution of watermark in the body image, and get the best balance between robustness and visibility, so wavelet has got the extensive application in the watermarking domain. This thesis mainly discusses meaning watermarking techniques based on the wavelet domain, addressing the selection of wavelet bases, gray watermark in wavelet domain; the icon watermark joined the image wavelet coding and other problems.Firstly, based on the brief introducing of wavelet theories and combine studies have being announced, pay attention to the familiar watermarking project which imbed watermark with the important coefficients of low frequency zone and high frequency zone in the wavelet domain, carry on the study to the selection valuation problem of wavelet bases. Attacking the image imbedded watermark with noise, filter and JPEG compression, Experiments' results show that the other wavelet bases are better than the biorthogonal wavelet bases, and wavelet D9, wavelet D4 and wavelet Haar are corresponding good for watermark in wavelet domain. This conclusion is significant for watermarking algorithm in wavelet domain.Secondly, arming at the problem that gray watermark has much more embed information than other watermark, and how to raise the robustness and visibility for gray watermark, in this thesis, a wavelet domain gray watermarking algorithm is proposed. The innovation of this algorithm lie in that it make best use of mankind's visual system (HVS) to imbed watermarking bit again and again with same coefficient ,so enlarge the watermarking capacity, and gave the theories certification. The results of experiment show that this algorithm leads to good invisibility and robustness, so it has actual applicant value.Finally, basing on the image wavelet coding (EZW, SPIHT, JPEG2000), this paper proposed a sign watermarking algorithm, the algorithm embed the watermarking bits in the 2-bit planes which be used in the cross of image wavelet coding, thus the algorithm has gradual characteristic, and the watermarking signal or watermarking image can be reconstructed gradually. In experiment, with two kind of watermarks included false random sequence watermark and 2-bit image watermark to verify the algorithm's usefulness, the result show that it still can detect the existence of the watermarking signal or extract good watermarking image from watermarked image which has be attacked even the coding rate is very low, for the normal attacking, the algorithm still has robustness.