Homework (I) Implementing the spread-spectrum watermarking system

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

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:

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

Informed S-S watermarking system * Ideal Case

Informed S-S watermarking system * Evaluation

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:

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

Blind S-S watermarking system Ideal Case

Blind S-S watermarking system * Evaluation ?

Multiple watermarking system

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

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

Rules Deadline：2008-11-05 14:00 繳交方式 將整份程式及說明文件壓縮成一個檔案，以附件寄至助教信箱（shadow@cmlab.csie.ntu.edu.tw）。 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。