Researches On Static Image Watermarking Technology Based On Discrete Cosine Transform

Along with the computer communication and the Internet technology development, multi-media data have beening widely spreaded through the network.A wide range of tort behavior catches a wide attention in the industry of video, film and television and the software.It faces great challenges that how to protect digital products copyright and prevent illegal copying.In the context of this, digital watermarking technology has been rapid development.It provide a credible evidence by embedding a number of identification information in multimedia data for the integrity and copyright ownership of multimedia data which can be used to prevent digital piracy and illegal copying of the products.This article first briefly introduces the research status of digital watermarking technology, given the common basic principles of digital watermarking technology and method, and then study the robust digital watermarking technology based on discrete cosine transform domain intensively. In this paper, two watermarking algorithms have been proposed which use binary image and grayscale image as a watermark respectively.It embed watermark information through modifying DCT coefficients of host image which firstly performs block-wise DCT.The proposed algorithm uses the human visual system features to calculate the Just Noticeable Difference threshold of DCT coefficients that can be use to control the weight factor of watermark.The main research contents include:(1)Proposed an improved watermarking algorithm that uses JND threshold for binary image based on an existing watermarking algorithm,which exchange directly DCT coefficients,and compare the performance between them by simulation(2)Proposed a novel watermarking algorithm which uses grayscale image as a watermark based on AC Coefficients Prediction.The Proposed algorithm hides data by appling blockwise DCT.The difference is that most of the information of watermark signal is embedded in the DC coefficients.In Extracting procedure,the watermark image is reconstructend by AC coefficients prediction. Simulation results shows that the Performance of the proposed watermarking algorithm is also invisible and robust even if the hose image have a larger data load.