Robust Reversible Watermarking Algorithm For Anti-geometric Attack

As an information hiding technology,digital watermarking embeds the watermarks into the digital media.It can not only extract the watermarks accurately,but also stay transparent for the user at the same time.Digital watermarking technology has been developing for more than 20 years,and many watermarking algorithms have been proposed and utilized.The main areas of researches are reversible digital watermarking and robust digital watermarking.These two kinds of watermarking have their own advantages,but also have obvious shortcomings.The robustness of the reversible digital watermarking is poor,and the robust digital watermarking cannot restore the original image.In order to solve the above problems,robust reversible watermarking has been proposed.It combines the advantages of robust watermarking with reversible watermarking.When the picture is attacked,the watermarks can be extracted accurately.When the picture is not attacked,we can not only extract the watermarks,but also can restore the original image.In the process of transmission,the image will not only be compressed,filtered and other conventional processing,but also suffered geometric arrack,such as rotation,scaling and so on.Therefore,robust reversible watermarking algorithm needs to resist geometric attacks.By studying and summarizing the existed algorithms,we proposed a robust reversible watermarking algorithm.It has the reversibility of digital watermarking and is able to resist known geometric attacks.At the stage of designing the algorithm,the picture is divided into two parts by the threshold segmentation method,one part used to embed the robust watermarks,and the other part to embed the reversible watermarks.First,the two parts are subjected to corrosion expansion operation and the centroid of the maximum connected domain of each part is obtained.The part which is embedded robust watermarks,is divided by some parallel lines,having the same slope as the two centroids and the average pixel value of each block is obtained.The robust watermarks are embedded by the parity method.The changes in each block should be recorded and the overflow should be recorded by bitmaps.And then changes,bitmap and centroid coordinates are embedded in another part of the image using the Pixel Value Ordering(PVO).When the reversible watermarks are embedded,the pixel value of the image is only reduced.In this paper,the robust watermarking embedding algorithm and the reversible watermarking embedding algorithm are improved and optimized,and the centroid of the image is used,so the pixel valuechanges will not affect the image segmentation,and the algorithm has the ability to resist geometric attacks.The algorithm proposed in this paper is robust reversible watermarking algorithm for gray scale images.Through simulation experiments,the results show that the algorithms is reversible and can resist known geometric attacks.Our proposed method has important implications for robust reversible image watermarking.