改進浮水印在對數極座標系

An Improved Watermarking Approach in the Log-polar Coordinate System

郭治廷(Chih-Ting Kuo)

指導教授 ： 楊致芳

國立臺北大學/電機資訊學院/通訊工程研究所/碩士(2009年)

摘要

在影像上藏入浮水印是為了防止駭客對未被授權的版權使用和惡意的改變內容。在許多的數位浮水印嵌入系統中，浮水印的取回原理主要建立在已知浮水印嵌入時的嵌入位置。然而幾何失真會重新排列浮水印的嵌入位置，因而導致浮水印取回的失敗。本篇論文所提出的機制便是針對解決幾何失真中的旋轉、縮放、平移為目標。
本論文裡提出一種浮水印演算法可對抗旋轉、縮放、平移的變形。浮水印資料被嵌入到對數極座標振幅頻譜中，對數極座標的振幅頻譜是將影片經傅立葉轉換到傅立葉頻譜，再轉換到對數極座標振幅頻譜，然後使用函數去從極座標擷取出浮水印的頻譜。對被藏入浮水印的圖片旋轉結果使得擷取出來的頻譜產生循環位移，對圖片縮放結果使得萃取出來的頻譜縮放，圖片位移對於擷取出來的頻譜沒有影響。因此計算循環位移的相關變數去做偵測。
誤測率結果是用12 張圖片跟1000 個浮水印去偵測。強健性結果使用12張圖跟1000 個浮水印去測量。實驗結果表示這設計是可以對抗幾種攻擊，如：旋轉、旋轉加上切割，縮放，縮放加上切割、位移、位移加上切割和JPEG 的壓縮。

關鍵字

數位浮水印,旋轉,縮放,位移,對數極座標

並列摘要

The purpose watermarking an image is to keep hackers from unauthorized use of copyrighted contents as well as malicious modification. In many digital watermarking systems, the basic principle to retrieve the watermark is based on the knowledge of the positions for embedding the watermark. However, geometric distortions such as rotation, scaling, and translation (RST) may rearrange watermark positions, and often result in the failure of the watermark retrieval. In this thesis, the proposed scheme aims to develop a watermarking method to be resilient to rotation,
scaling, and translation of the geometric distortions.
Watermarking algorithm that is robust to RST distortions in this paper. The watermark data sequence is embedded into the log-polar mapping (LPM) magnitude spectrum, which is obtained by taking the Fourier transform of the cover image, and transforming the corresponding Fourier magnitudes into log-polar magnitude spectrums. For watermark detection, a function is designed to extract
watermark-related magnitudes along the polar-radius axis. In the proposed approach, rotating the watermarked image results in a cyclical shift of the embedded watermark data, scaling the image results in amplification of the embedded
watermark data, and translating the image has no effect on the embedded watermark data. Correlation coefficient is adopted as the detection measures.
False positive results on a set of 12 images with 1000 watermarks are tested, as well as the properties of robustness are described. The experimental results have
shown that the proposed scheme is robust to several attacks such as rotating, rotating with cropping, scaling, scaling with cropping, translating, translating with cropping, and JPEG compression.

並列關鍵字

digital watermarking, rotation, scaling, and translation (RST), log-polar

參考文獻

[1] C. Lin, M.Wu, J. Bloom, I. Cox, M. Miller, and Y. Lui, “Rotation, scale, and translation resilient watermarking for images” IEEE Trans. Image Processing, vol. 10, May 2001, pp. 767–782.

[2] Xiangui Kang, Jiwu Huang, Yun Q. Shi, and Yan Lin, “A DWT-DFT composite watermarking scheme robust to both affine transform and JPEG compression” IEEE Transaction on Circuits and Systems for Video Technology, vol. 13, No.8,

August 2003.

[3] M. Kutter, “Watermarking resistance to translation, rotation, and scaling” in Proc. SPIE: Multimedia Systems Applications, vol. 3528, 1998, pp. 423–431.

Signal Processing Conf. (EUSIPCO’2000), Tampere, Finland, Sept. 2000.