Post on 11-Feb-2016
description
By Elo Leung and Wing WongCS 265 Section 2
Spring 2004
Table of Contents1. Project Objectives2. Watermarking in General3. Attacks on Watermarks4. Desired Characteristics of Invisible Watermarks5. Spread Spectrum Watermarking
– Insert & Extract Watermark6. Example7. Advantages & Disadvantages8. Conclusion
Project Objectives
- Analyze the spread spectrum watermarking algorithm proposed by Cox et al.
- Demonstrate the application of Cox’s algorithm using a sample image file
Watermarking in Generalthe 3 components:
1. Watermark
2. Encoder – watermark insertion
3. Decoder and Comparator – watermark extraction and verification
Watermarking in Generalthe 3 components:1. Watermark2. Encoder3. Decoder and ComparatorEncoder
Original WatermarkedImage (I ) Image (I' )
Signature (S )
E
Figure provided by Mohanty [2].
Watermarking in GeneralUses 3 components:1. Watermark2. Encoder3. Decoder and Comparator
Decoder Comparator
Test Extracted match/Image (J ) Signature (S' ) mismatch
Origianal Image (I ) Origianal Signature (S )
D C
Figure provided by Mohanty [2].
Attacks on Watermark
Transmission
Lossy OtherCompression International
TamperingsProcessing
I
I'
Watermarked Object
Corrupted Object
Transmission
Typical Distortions and International Tampering
GeometricalDistortion
CommonSignal
Figure provided by Cox et al. [1].
Attacks on Watermark
Transmission
Lossy OtherCompression International
TamperingsProcessing
I
I'
Watermarked Object
Corrupted Object
Transmission
Typical Distortions and International Tampering
GeometricalDistortion
CommonSignal
Irreversible Data Loss
Quality Degradation
e.g. JPEG/MPEG
Attacks on Watermark
Transmission
Lossy OtherCompression International
TamperingsProcessing
I
I'
Watermarked Object
Corrupted Object
Transmission
Typical Distortions and International Tampering
GeometricalDistortion
CommonSignal
Specific for images/videos
rotation, translation, scaling, and cropping operations
Attacks on Watermark
Transmission
Lossy OtherCompression International
TamperingsProcessing
I
I'
Watermarked Object
Corrupted Object
Transmission
Typical Distortions and International Tampering
GeometricalDistortion
CommonSignal
analog-to-digital, digital-to-analogconversion, etc.
Attacks on Watermark
Transmission
Lossy OtherCompression International
TamperingsProcessing
I
I'
Watermarked Object
Corrupted Object
Transmission
Typical Distortions and International Tampering
GeometricalDistortion
CommonSignal
Rewatermarking
Desired Characteristics of Invisible Watermarks
1. Perceptually unnoticeable
2. Robust to common watermark attacks
3. Quality degradation upon removal of watermarks
4. Unambiguously identifies the owner of the digitized medium (audio, video, or image).
Spread Spectrum WatermarkingSpread Spectrum Watermark = Invisible Watermark
Key: • Insert watermark at perceptually significant regions
• Spread watermark throughout the data
**Data = audio, video, or image file
Spread Spectrum WatermarkingInsertion Process
Original Image (V)
Spectrum
Watermark (X) Insert Modified Normally Distributed watermark Spectrum
WatermarkedImage (V')
Determine percetually significant regions
Inverse FFT/DCT
FFT/DCT
Figure provided by Mohanty [2].
v'i = vi (1 + αxi)
Spread Spectrum WatermarkingExtraction Process
RecoveredImage (I')
RecoveredSpectrum
Original FFT/ Original Image (V) DCT Spectrum
ExtractedWatermark (X*)
does not similar? belong
to owner yes
belongs toowner
noOriginal Watermark (X)
-
Figure provided by Mohanty [2].
sim(X, X*) = (X X*) sqrt (X X*)
Example
(1) Original (2) Watermarked Differences of (1) & (2)
Advantages & DisadvantagesAdvantages:
• Not noticeable since the watermarks are spread out.
• Can’t be removed without severe quality degradation since watermarks are inserted at perceptually significant regions.
Disadvantages:
• Original watermark is required in the extraction process.
Conclusion
Spread spectrum watermarking:
• Can be used for audio, video, and image files
• Meets the desired characteristics of invisiblewatermarks – unnoticeable, robust, unambiguous
References:
[1]Ingemar J. Cox, et al., “Secure Spread Spectrum Watermarking for Multimedia”, IEEE Trans. on Image Processing, Vol. 6, No.12, Dec 1997, pp.1673-1687. [2] Saraju P. Mohanty, “Digital Watermarking: A Tutorial Review”, Department of Computer Science and Engineering, University of South Florida. [3] Peter Meerwald, “Digital Image Watermarking in the Wavelet Transform Domain”, Master’s Thesis, Department of Scientific Computing, University of Salzburg, Austria, January 2001.
[4] http://www.cosy.sbg.ac.at/~pmeerw/Watermarking/source/
The End