Invisible Watermark By Elo Leung and Wing Wong CS 265 Section 2 Spring 2004
Table of Contents • Project Objectives • Watermarking in General • Attacks on Watermarks • Desired Characteristics of Invisible Watermarks • Spread Spectrum Watermarking • – Insert & Extract Watermark • Example • Advantages & Disadvantages • 8. 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 General • the 3 components: • Watermark • Encoder • – watermark insertion • Decoder and Comparator • – watermark extraction and verification
Watermarking in General • the 3 components: • Watermark • Encoder • Decoder and Comparator Figure provided by Mohanty .
Watermarking in General • Uses 3 components: • Watermark • Encoder • Decoder and Comparator Figure provided by Mohanty .
Attacks on Watermark Figure provided by Cox et al. .
e.g. JPEG/MPEG Irreversible Data Loss Quality Degradation Attacks on Watermark
Attacks on Watermark Specific for images/videos rotation, translation, scaling, and cropping operations
analog-to-digital, digital-to-analog conversion, etc. Attacks on Watermark
Attacks on Watermark Rewatermarking
Desired Characteristics of Invisible Watermarks • Perceptually unnoticeable • Robust to common watermark attacks • Quality degradation upon removal of watermarks • Unambiguously identifies the owner of the digitized • medium (audio, video, or image).
Spread Spectrum Watermarking • Spread 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 v'i = vi (1 + αxi) Figure provided by Mohanty .
sim(X, X*) = (X X*) sqrt (X X*) Spread Spectrum WatermarkingExtraction Process Figure provided by Mohanty .
Example (1) Original (2) Watermarked Differences of (1) & (2)
Advantages & Disadvantages • Advantages: • 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 invisible • watermarks – unnoticeable, robust, unambiguous
References: 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.  Saraju P. Mohanty, “Digital Watermarking: A Tutorial Review”, Department of Computer Science and Engineering, University of South Florida.  Peter Meerwald, “Digital Image Watermarking in the Wavelet Transform Domain”, Master’s Thesis, Department of Scientific Computing, University of Salzburg, Austria, January 2001.  http://www.cosy.sbg.ac.at/~pmeerw/Watermarking/source/