Homework (I) Implementing the spread-spectrum watermarking system

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1 Homework (I) Implementing the spread-spectrum watermarking system

2 Reference Ingemar J. Cox, Joe Kilian, F. Thomson Leighton, and Talal Shamoon, "Secure Spread Spectrum Watermarking for Multimedia," IEEE Trans. on Image Processing, Dec. 1997

3 Embedder (with original C)
The watermark X = x1 x2 … xn ( ex. n = 1000 ) xi ~ N(0,1) Use Sign(.) to convert xi into 1 or -1 The Cover Image C is transformed by N×N DCT. Ct=DCT(C). The coefficients to be altered V = v1 v2 … vn (n largest magnitude coefficients in the Ct except DC) The scaling parameter α ( ex. α=0.1 ) Embedding:

4 Informed Extractor (with original C)
The distorted coefficients V* = v*1 v*2 … v*n (n largest magnitude coefficients in the Ct except DC) The extracted watermark X* = x*1 x*2 … x*n

5 Informed S-S watermarking system * Ideal Case

6 Informed S-S watermarking system * Evaluation

7 Embedder (without original C)
The watermark X = x1 x2 … xn ( ex. n = 1000 ) xi ~ N(0,1) Use Sign(.) to convert xi into 1 or -1 The Cover Image C is transformed by N×N DCT. Ct=DCT(C). The coefficients to be altered V = v1 v2 … vn (the first n coefficients according to the zigzag order in the Ct except DC) The scaling parameter α Embedding:

8 Blind Extractor (without original C)
The distorted image C* is transformed by N×N DCT. C*t=DCT(C*). The distorted coefficients V* = v*1 v*2 … v*n (the first n coefficients according to the zigzag order in the C*t except DC) The extracted watermark X* = x*1 x*2 … x*n

9 Blind S-S watermarking system Ideal Case

10 Blind S-S watermarking system * Evaluation
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11 Multiple watermarking system

12 Multiple watermarking system - Challenges
Challenge 1 – Extract exactly correct message Increase α? Change the embedding process to Challenge 2 – Maximize the number of watermarks Find out the optimal k Challenge 3 – Improve the fidelity (PSNR or SAD) of embedded image

13 Attack Lossy Compression JPEG compression Geometric Distortion
Rotation Cropping Image Processing Blurring

14 Rules Deadline：2008-11-05 14:00 繳交方式
主旨格式： MMSec2008_Homework1_學號_姓名 附件檔名格式：MMSec2008_Homework1_學號_姓名.rar or .zip 評分標準 程式功能（30%）：可 embed 及 extract watermark message。 書面報告（70%）： 須詳細解釋如何執行繳交的程式； 須包含 marked image 與 original image 的 PSNR及類似第六頁的圖表（ 即用另外 999 個不同的 watermark extract）； 須包含各項常見攻擊（見第十三頁，至少需九種）對此浮水印機制所造成的影響，並整理成圖表。