Research On Watermark For Engineering Graphics Based On Fractional Fourier Transform

Digital watermarking is a kind of information hiding technology, and is an effective new method to protect property. Recently, it has become an important research topic in digital domain. At present time, research on digital watermarking mostly focuses on images, video, text and so on. However, engineering graphic as a kind of graphic digit, its property protection problem is also very important. These years watermarking on graphic data has been gained more attention.This dissertation focuses on watermark algorithm for engineering graphics based on fractional Fourier transform, which has double-domain characteristic. The main achievements of this thesis are as follows:1. This paper discusses the basic purposes of digital watermarking, its principles, the main techniques, and application domain. The current state of research in this field is reviewed. It also analyses the theories and properties of fractional Fourier transform and make some comparisons between watermark algorithms for images and graphics. The characteristics and current state of research in 2D graphics'watermarking are generalized.2. Propose a non-blind detection watermarking algorithm for 2-dimensional engineering graphics based on fractional Fourier transform. The watermark is embedded into the fractional Fourier transform spectrum of vertex set. In order to enhance the robustness against entities'deleting, vertices are divided into groups due to coordinate position, and the watermark is embedded repeatedly. Experiment results show that the algorithm is robust and safe.3. Considering the application limitation of non-blind detection watermarking, this thesis proposes a blind watermarking algorithm for 2D engineering graphics based on fractional Fourier transform. In this method, the relative coordinate vectors of the lines were extracted from graphics for constructing a 1D complex signal. Watermark is embedded into the radio of the modules of fractional Fourier transform coefficients of the complex signal according to the value of the watermark, as fractional Fourier transform has linear property. This method is a blind detection algorithm, original graphic is not needed in watermark extraction. Experiment results show that the method is transparency. It is robust against attacks such as moving, rotation, scaling, and is also safe towards illegal information extraction.