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Blind Watermark Detection on MPEG4-2D Mesh Animation
報告者:梁晉坤指導教授:楊士萱博士
Outline Public and Private Watermarks Wavelet Transform Watermark Embedding Watermark Detection Simulation Results
Public and Private Watermarks Public watermarks are those where an
end user of the data is able to extract the watermark. (Blind detection, the original work is not need)
Private watermarks are those where watermark extraction requires secret information known only to the watermark embedder. (informed detection, the original work is need)
Wavelet Transform Multiresolution representation Two methods of wavelet transform
Convolution Lifting
Realizing discrete time wavelet transform by “Filter Bank”
Analysis and Synthesis
h0(t)
h1(t)
2
2y1
y0
X2
2
g0(t)
g1(t)
X’
Analysis Filter Synthesis Filter
Multiresolution Representation
Original
L1 H1
L2 H2
……
Lp Hp
Local
Global
h0(t)
h1(t)
2
2y0,1
y0,0
2‘th level decomposition
1‘th level decomposition
h0(t)
h1(t)
2
2y1
y0X
Watermark Embedding Step 1, embedding component
selection Select larger component (X or Y) In tie, select X component
Step 2, perturbing selected component Bit=1, positive direction Bit=0, negative direction
Record Key file for blind detection
X>Y X<Y X=Y
Watermarking Bit = 1/ 0
Watermark Detection Informed detection(Hard decision)
According to Original mesh and Attack mesh to extract watermark sequences
If PointW>=pointO extractBits push 1 else extractBits push 0
Counting correct bits from extract bits Original mesh is need
Informed detection(Soft decision) According to Attack mesh and key file
to detect whether watermark is embedded.
Original mesh is not need, but some of the original mesh coefficients mush be saved in the key file.
Correlation: Original Correlation
Embedded Correlation
n
i
iMOiCorrO1
*
If m=1 then Mi=1, else if m=0 then Mi=-1
n
i
ii MECorrE1
*
Attacked Correlation
If CorrA <= CorrE+Thres and CorrA>= CorrE-thres then watermark is embedded. Otherwise watermark is not embedded.
n
i
ii MAECorrA1
*
Correlation Coefficient CorrCoef(X,Y)=Corr(X,Y)/
SigmaX*SigmaY SigmaX = sqrt(E[X2]-(E[X])2) SigmaY = sqrt(E[Y2]-(E[Y])2) Corr(X,Y) = E[XY]-E[X]E[Y] -1=<CorrCoef(X,Y)<=1
X:Original Coefficients Y:Embed Coefficients Z:Attack Coefficients W:Watermark Sequences(1, -1)
Compute CorrCoef(Y-X,W) , CorrCoef(Z-X,W), CorrCoef(X,W), CorrCoef(Y,W) and CorrCoef(Z,W)
If CorrCoef(Z-X,W)> threshold, we consider watermark is detected. Otherwise, watermark is not detected
Simulation results(Parameters) Mesh12
MPEG-4 conformance testing 128 MOPs, each MOP has 120 points
and 187 triangles Threshold=0 Watermark, 127 bits PN code Quality=0.01 (MMSE) Resolution level : 2,4,6
Working environment GTS
Mesh12 FindWI_Mesh12 par_final_mesh12_128_001
Key File Intensity CorrO, CorrE,(Original Coefficients) Embedded Location
Affine attack
Item
Scaling
Rotate degree
Translate distance
1 1.3 0 (12, 0)
2 1 25 (0,5)
3 0.7 65 (-11,-9)
Smoothing attack Smooth filter
S3={1/4,1/2,1/4} S5={1/5,1/5,1/5,1/5,1/5}
Other Attacks Simplifying attack Enhancement(1.5) and
Attenuation(0.6) RNTest RNMVTest RNMVAffineTest