Research On Digital Image Watermarking Algorithms

With the rapid development of computer network technology and the enhancement of public consciousness of copyright protection, the security of digital information becomes very important. The digital watermarking technology emerges as the times require. As an effective method for copyright protection, the digital watermarking technology has acquired more and more attention.The main task in this paper is focused on digital image watermarking that based on spatial domain and DCT domain. The principle of digital watermarking based on spatial domain algorithms is that, the watermarker is embedded by modifying the pixel, so it is simple and easy. Discrete cosine transform is one of the most common linear transformations in digital signal processing technology. This transformation has good energy compression and the ability to remove correlation. So it is getting more and more attention in watermarking technology. Through the research, two kinds of digital watermarking algorithms based on spatial domain and one based on DCT domain are proposed.1. Two kinds of digital watermarking algorithms based on spatial domain are brought forward in this paper.(1)When the watermark energy is distributed uniformly in the energy of the carrier image, the safety of the algorithm will be improved. This characteristic is fully utilized in the first algorithm. The watermark is embedded evenly and smoothly by changing the pixels of the image sub-block regularly. Adding a series of pre-processing including Arnold transform,chaos encryption to watermark data before embedding enhanced the anti-attack performance of watermark. The raw carrier image is needed when extracting the watermark, so it is not a blind watermarking algorithm, but by using multiple keys, the algorithm becomes more safety.(2)The mean value of sub-block has good ability to withstand the attack, based on that, the second algorithm is proposed. According to the various sub-block texture complexities, quantization step length is selected, so that the requirements of imperceptibility are satisfied. Then, the mean value of the sub-block is calculated and quantified. Each watermark data is represented by the change of the overall data of the sub-block. By using the method of quantization, the blind image watermarking extraction is realized.2. One kind of digital watermarking algorithm based on frequency domain is presented. Using the spatial frequency characteristics of HVS, appropriate areas are selected for watermark embedding. And each image sub-block which has different texture characteristic is embedded by different strength.Because of that after several kinds of image processing, the parameters around the embedding positions may be changed; the mean value of the DCT coefficients around it is calculated. The values on the embedding positions are replaced by the sum of the mean value and the value of the watermark, so the robustness of the watermark is enhanced.In the simulation experiments, gray image is used as carrier image, and a meaningful binary picture used as watermark signal, the result is intuitionistic and believable. Experimental results demonstrate that the three algorithms can satisfy the requirements of imperceptibility and robustness. And the last two algorithms are more practical, because they do not need the original carrier data when extracting the watermark.