Research On Anti-distortion Holographic Watermarking Algorithm Based On Image Feature Points

With the diversification of human life styles,the application of digital images in daily life has become more popular.However,today's highly developed network technology has severely threatened the security of digital images.In this severe situation,digital watermarking technology has entered people's field of vision,and has been highly concerned by a large number of scholars in recent years.In practical applications,watermarked images are often damaged or attacked.How to improve the robustness of watermarked images has become a bottleneck problem for this technology to be widely used.This paper focuses on the research of digital image watermarking technology which can resist geometric attack.The main work and research results are as follows:(1)In order to improve the robustness and security of digital watermarking,I carried out the research on the algorithms of CGH watermarking and Digital Holographic Watermarking.The programming has realized the four-step phase shift method in digital holography and the Boch coding algorithm in computational holography,and completed the generation of hologram and image reconstruction.According to the different designed watermarking algorithms,the appropriate holographic calculation method is selected to realize the embedding and extraction of digital holographic watermarking in the carrier image.(2)In order to realize the anti-geometric attack of the watermark,I carried out the research of the anti-geometric holographic watermark algorithm based on DCT and DWT.Firstly,the four-step phase shift method is used to calculate and generate a digital watermark hologram,and then the DWT and DCT algorithms are used to perform DWT and DCT transformation on the carrier image.In the transform domain,the holographic watermark spectrum is embedded in the carrier image spectrum,and then the embedding of the hologram watermark in the carrier image is completed by inverse DWT and DCT transformation.The embedding method of realizing holographic watermarking in transform domain is better than the embedding method based on space domain.The robustness of the algorithm has been improved very well,so that the watermark can resist the conventional geometric transformation attacks.(3)Aiming at the problem that the second-generation digital watermarking can not resist nonlinear geometric attacks well,this paper also proposes a robust watermarking algorithm combining SIFT feature points and holographic watermarking.The original watermark is transformed into a computer-generated hologram by using the Borch coding method,and the watermark is embedded according to the feature points extracted from the carrier image.The watermark is extracted and reconstructed by matching the feature points in the original carrier image and the feature points in the carrier image containing the watermark.This algorithm has further enhanced the robustness,and can still be used when the image is distorted.It can resist not only conventional attack and geometric attack,but also random distortion,ripple distortion,cosine transformation and other nonlinear geometric attacks.