Research On Digital Image Watermarking Algorithm Based On Naturalness Preserving Transform

With the development of digital multimedia and network communication, it makes the storage, coping and transmission of digital information easier, while the problems of copyright protection, information security and identification that followed have become urgent problems to be solved. Digital watermarking technology becomes an important way to solve these problems because of its invisibility, robustness and security.Introducing the characteristic, evaluation standard, key technique and research status at home and abroad of digital watermarking technology, the paper analyzes that the spatial domain algorithm is visible and easy to be decoded and its robustness is poor. On the other side, the transform domain algorithm has the following disadvantages: small information capacity and poor invisibility. Accordingly, this paper puts forward a new image watermarking scheme which is based on Naturalness Preserving Transform (NPT), wavelet image combination and chaotic scrambling, and which also improves the invisibility, robustness, and security of watermarking.The main research work is as follows:1. Doing research on the properties of reconstruction and compensation of the Naturalness Preserving Transform (NPT). Proposing an algorithm which is between spatial domain and transform domain. This algorithm is used in the process of insertion and extraction of watermark, promoting the invisibility and proving the robustness of watermark. Simulating experiments show that by this way, the watermark can be extracted completely and it can resist JPEG compression, cropping, scaling, rotation and noises efficiently.2. Analyzing the characteristics of multi-resolution analysis and multi-frequency fusion of wavelet image combination, the paper proposes an integration algorithm on basis of wavelet fusion technique and NPT, to promote the invisibility and visual effect of watermarked image. The simulation results prove that compared with Butterworth Low Pass Filter, wavelet image combination does better in improving the quality of watermarked image.3. Discussing that watermarking can be easily generated by chaotic scrambling and has good security, the paper proposes that awaiting watermark image should be scrambled by Arnold chaotic system firstly to make it hard to decrypt and recover, promoting the safety performance.By lots of simulation experiments, the paper verifies the robustness, security, and good visual quality of this scheme and puts forward the further research thoughts and direction.