Study of Improved Digital Watermarking Techniques

• Main Authors: Huang-Chi Chen, 陳煌琦
• Other Authors: Rey-Chue Hwang
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/38482159264482769374

博士 === 義守大學 === 電機工程學系 === 102 === In this dissertation, several improved and advanced methods for the watermarking techniques are presented. With the fast development and popularity of internet, more and more information communication and transmission are carried out by internet. It is well known that due to the consideration of bandwidth, the digital signal must be compressed firstly before the signal is transmitted. In all of the methods of signal compression, JPEG (Joint Photographic Experts Group) is the most common method used for the digital image’s compression, particularly for those images produced by digital photography. JEPG could also be treated as a standard of image compression. However, the basic requirement for the robustness of the watermarking mechanism should have the ability to resist the attack of JPEG and still be able to provide the protection of digital information copyright. In the process of JPEG quantification, two similar DCT (Discrete Cosine Transformation) coefficients could possibly be quantified to the same level. To the watermarking technique on the frequency domain, such condition might cause the mistake of the extracting watermark from the lossy compression of the watermarked image. For the practical application, the watermarking technique should have the ability to extract the exact watermark without the information of the original host image. In this research, an important issue was discussed and studied. This issue is about how to make the qualities of the watermarked image and the retrieve watermark can reach the best trade-off. In this research, several methods are presented for improving the technique of watermark. First method is to adjust the quantized coefficients by using two auxiliary variables and then reach the improvement of the error. Second method uses the absolute value idea to prevent the sign change due to the over adjustment of the quantized coefficients. At last method, a watermarking technique by the modulation method based on Reed-Solomon code is proposed. The DC (direct current) value, low-frequency coefficient, the inter-block correlation are used to create the message of RS codes and then RS codeword could be produced. The redundancy vector will also be embedded into the image. The results of RS decoder will be used to judge the watermark. In the whole study, each method will be experimented and the experimental results will be used evidence the feasibility of the method proposed.