Digital Watermarking Using Phase Digital Watermarking Using Phase Dispersion --- UpdateDispersion --- Update

SIMG 786 SIMG 786

Advanced Digital Image ProcessingAdvanced Digital Image Processing

Mahdi Nezamabadi, Mahdi Nezamabadi,

Chengmeng Liu, Chengmeng Liu,

Michael SuMichael Su

OutlineOutline

• Carrier design

• Embedding and extraction for single tile and Multi-tiles (improving the robustness)

• Parameter α selection and invisibility

• Moment Normalization• Rotation/Scale Detection

Carrier Implementation 1Carrier Implementation 1

• Carrier is implemented in frequency domain

• Carrier has random phase

• The amplitude of Carrier is high pass in order to make it invisible in spatial domain

• Carrier should be symmetric in frequency domain in order to make its imaginary part to 0 in spatial domain

Carrier Implementation 2Carrier Implementation 2High-pass vs. All-passHigh-pass vs. All-pass

Carrier Implementation 3Carrier Implementation 3

• Auto correlation of Carrier function should approximate delta function

• The average of Carrier should be 0

Carrier Implementation 4Carrier Implementation 4if Carrier is not symmetric in frequency domainif Carrier is not symmetric in frequency domain

Embedded MessageEmbedded Message

*• Convolution is

implemented by multiplication of Fourier transform in frequency domain

• Zero padding must be performed before FFT

Tiling Improves the RobustnessTiling Improves the Robustness

Tiling Improves the RobustnessTiling Improves the Robustness

• After 8 by 8 tiling, the summation of tiles is shown at right

• The amplitude of the input image will be averaged to flatten after summation of 64 tiles

• The watermark information is amplified

Parameter Parameter αα = 0.1 = 0.1

αα = 0.05 = 0.05 αα = 0.1 = 0.1 αα = 0.3 = 0.3 αα = 0.5 = 0.5 αα = 0.7 = 0.7

Parameter Parameter αα = 0.3 = 0.3

αα = 0.05 = 0.05 αα = 0.1 = 0.1 αα = 0.3 = 0.3 αα = 0.5 = 0.5 αα = 0.7 = 0.7

Parameter Parameter α = 0.5 = 0.5

αα = 0.05 = 0.05 αα = 0.1 = 0.1 αα = 0.3 = 0.3 αα = 0.5 = 0.5 αα = 0.7 = 0.7

Parameter Parameter α = 0.7 = 0.7

αα = 0.05 = 0.05 αα = 0.1 = 0.1 αα = 0.3 = 0.3 αα = 0.5 = 0.5 αα = 0.7 = 0.7

Similarity vs. Similarity vs. α

• Similarity is measured by cross correlation between original and extracted log

• 64 tiles were used in embedding

• The α controls the visibility of the watermark logo in the watermarked image

• The α also depends on the number of tiles

Attacked by low pass filterAttacked by low pass filter

• The watermarked image is blurred

• The extracted logo is equivalent to original log convolve with a low pass filter

α=0.3,no blurred α=0.3,blurred

Moment NormalizationMoment Normalization

• Preprocessing to remove the high amplitude, low frequency noise

• At flat area, v’ is replaced by random number with variance of σd

Rotation/Scale DetectionRotation/Scale DetectionThreshold and image DilationThreshold and image Dilation

Rotation/Scale DetectionRotation/Scale DetectionImage rotationImage rotation

Rotation/Scale DetectionRotation/Scale DetectionImage rotationImage rotation

Current Issues and ProblemsCurrent Issues and Problems

• Odd and Even dimensions of Carrier function generate different output result in spatial domain.

• How to deal with interpolation errors during rescaling and re-rotation processes

Follow-up WorksFollow-up Works

• Implement Contrast Sensitivity Function in Carrier function design

• Rotation/Scale pattern detection • Rotate back to right orientation and scale back

to its original dimensions• Implementation of Binary Message template

function• Integrate all functions and final presentation and

report

Thank You!Thank You!

Question?Question?