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