Dynamic Control of Quantization Coefficient for Watermarking

As technology of multimedia communication has developed, there follow some side-effects such as duplication of digital image information and copyright infringement. For the purpose of protecting digital image information, many researches have been made in the field of watermarking technology. For the protection of copyright, in this paper, we proposed and watermarking algorithm in which invariable sign of DCT coefficients should be used and by which the quality of digital image can be preserved. According to the algorithm, through the calculation of the sing DCT coefficients and the use of high and low frequency elements, position of watermark and size value should be decided and thereby the quantization value should be adjusted. By so doing, the algorithm can improve image quality (PSNR) and obtain good efficiency with which strong watermark can be inserted into the digital image.