Concepts of Multimedia Concepts of Multimedia Processing and TransmissionProcessing and Transmission

IT 481, Lecture #9Dennis McCaughey, Ph.D.

2 April, 2007

04/02/2007IT 481, Spring 20072

ProjectProject

Project will be recovering a student specific watermark from the bird image.

MATLAB code will be provided you only have to execute it. This is not a programming project.

e-mail me at dennisgmc1@verizon.net– I will reply with the code.

Criteria:– Recover the watermark– Assess the visibility and robustness of the

watermarking method

04/02/2007IT 481, Spring 20073

Homework #4Homework #4

E-mail “dennisgmc1@verizon.net” requesting MATLAB code and “bird” picture.

I will reply with the code. Load these on a CD and bring to 4/9 class Review the following instructions

– Insert the CD – Open Matlab– Under “file” open D\:watermarkread.m– Under “debug” click “run”– When prompted, set the search path to the top of the Matlab

search order, click “ok”– When prompted, enter your student ID #

Project– Answer the following questions

What is the embedded message? How many errors are reported? The number of errors may not equal the misspelled words, Why?

– E-mail your answers to me by 4/13

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WatermarkingWatermarking

Watermarking is a secret code described by a digital signal carrying information about the copyright property of the product.

The watermark is embedded in the digital data in such a way that it is not visually perceptible.

The copyright owner should be the only person who can show the existence of his own watermark and to prove then origin of the product.

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Watermark RequirementsWatermark Requirements

Alterations introduced into the image or audio should be perceptually invisible.

A water mark must be undetectable and not removable by an attacker.

A sufficient number of watermarks in the same image or audio, detectable by their own key, can be produced.

The detection of the watermark should not require the original image or audio.

A watermark should be robust against attacks which preserve the desired quality of the image or audio.

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Main Features of WatermarkingMain Features of Watermarking

Perceptual Invisibility Trustworthy Detection Associated Key Automated Detection/Search Statistical Invisibility Multiple Watermarks Robustness

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Perceptual InvisibilityPerceptual Invisibility

Watermark should not degrade the perceived image/audio quality

Differences may become apparent when the original and watermarked versions are directly compared

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Trustworthy DetectionTrustworthy Detection

Watermarks should constitute a sufficient and trustworthy part of ownership.

False alarms should be extremely rare. Watermarks signatures/signals should be

complex. An enormous set of watermarks prevents

recovery by trial-and-error methods.

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Associated keyAssociated key

Watermarks should be associated with an identifiable number called the watermark key.

Key used to cast, detect and remove the watermark.

The key should be private and should exclusively characterize the legal owner.

Any signal removed from the image/audio is assumed to be valid only if it can be associated with the key via a well established algorithm

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Automated Detection/SearchAutomated Detection/Search

Watermark should combine with a search algorithm.

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Statistical InvisibilityStatistical Invisibility

Watermark should not be recoverable using statistical methods.

The possession of a great number of watermarked images, embedded with the same key should not enable the recovery of the watermark through statistical methods.– Watermarks should be image/audio

independent.

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Multiple WatermarksMultiple Watermarks

Multiple watermarks assist in the case where someone illicitly watermarks and already watermarked image/audio.

Convenient in transferring copyrighted material.

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RobustnessRobustness

A watermark should survive some modifications to the data.

Common manipulations to image/video– Data Compression– Filtering– Color, quantization , brightness modifications,

geometric distortions, etc– Other trans-coding operations.

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Application DomainsApplication Domains

A1: Carrying value-added metadata– Additional information such as hyperlinks, content based

indexing– Malicious and non-malicious attacks– Survive MPEG encoding

A2: Copy protection and conditional access– Control Intellectual Property Management and Protection– View and copy options– Every compliant decoder must be able to trigger protection

or royalty collection mechanisms at the time of decoding– Unauthorized individuals should not be able to defeat the

watermarks by any means A3: Ownership assertion, recipient tracking

– Establish ownership and determine origin of unauthorized duplication.

– Prosecution of copyright infringement

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Application Domains Cont’dApplication Domains Cont’d

A4: Authentication and verification– Allows fragile watermarks; if contents modified watermarks

should disappear. – Helps in identifying areas that wer modified

A5: Broadcast monitoring– Monitor where and when the contents are played– Advertisements. Here heavy content degradation is less of an

issue.– Watermark removal, invalidation and forgery can be significant

concern– Counterfeiting should be intractable for the system to be effective

A6: Secret communication or steganography– Data hiding may require higher capacity watermarks than other

applications– Secrecy may be the overriding concern in some applications

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AttacksAttacks

AT1: Basic attacks– Lossy compression, frame dropping & temporal rescaling

AT2: Simple attacks– Blurring, median filtering, noise addition gamma correction

and sharpening AT3: Normal attacks

– Translation, cropping and scaling AT4: Enhanced attacks

– Aspect ratio change & random geometric perturbations (Stirmark)

AT5: Advanced Attacks– Delete/insert watermarks, single document watermark

estimation attacks & multiple-document statistical attacks

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Robustness, Resilience & DetectionRobustness, Resilience & Detection

Applications Domain

Unintentional Attacks

Intentional Attacks Every

DecoderHigh

CapacityApplications

ExampleAT1 AT2 AT3 AT4 AT5

A1 Yes Yes Maybe No No Yes Yes Value-added metadata

A2 Yes Yes Yes Yes Yes Yes No Copy Protection

A3 Yes Yes Yes Yes Yes No No Ownership/fingerprint

A4 Yes No No No Some Yes No Authentication

A5 Yes Yes NO No Yes Yes Yes Broadcasting

A6 Yes Yes Maybe Maybe Yes No Yes Secret Communication

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Human PerceptionHuman Perception

Watermarking schemes take advantage of the fact that the human audio and visual systems are imperfect detectors.

Audio & visual signals must have a minimum intensity or contrast before they are perceptible.

These minima are spatially, temporally and frequency dependent.

These dependencies are either implicitly or explicitly exploited

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Transform Domain ConsiderationsTransform Domain Considerations

The human eye is more sensitive to noise in the lower frequency range than in the higher frequency counterparts

However, energy in most images is concentrated in the lower frequency range.

Quantization used in DCT based compression reflects the HVS which is less sensitive in the higher frequencies

A trade is required to balance watermark invisibility and survivability resulting in the use of the mid-frequency terms.

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Transform Domain ConsiderationsTransform Domain Considerations

An alteration of a transform coefficient is spread across the entire spatial block

A one dimensional example:

0 20 40 60 80 100 120 1400

0.5

1DCT Spectrum

0 20 40 60 80 100 120 1400

0.5

1Time Sequence

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Data Embedding AlgorithmData Embedding Algorithm

Embedding Algorithm

Perceptual Analysis

Key

SignalWith embedded data

Information

Signal(image, audio or video)

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Embedded Data ExamplesEmbedded Data Examples

Multilingual soundtracks within a motion picture

Copyright data Distribution permissions Data used for accounting and billing and

royalties Etc.

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Watermarking TechniquesWatermarking Techniques

Non-Blind: Watermark recovery requires the original

Blind: Watermark recovery does not require the original

Spatial domain or transform domain embedding

Spatial domain:– LSB, color pallet, geometric

Transform Domain:– FFT, DCT, Wavelet

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An Algorithm Proposed by Busch, Funk An Algorithm Proposed by Busch, Funk and Wolthusenand Wolthusen

A/DQuantize Y-

DCTRGB to YCbCr

Block DCT

EmbedInverse

Quantize Y-DCT

Inverse Block DCT

YCbCr to RGB

Camera

Digitized Video to MPEG-2

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Algorithm ConsiderationsAlgorithm Considerations

Watermark embedding position determined through a pseudo-random number generator that determines the order of block processing and the coefficient to be modified– Embed all available blocks

Key may be public or secret leading to a public or secret watermark

Redundantly embed the watermark to achieve survivability to MPEG-2 compression

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Selected Block EmbeddingSelected Block Embedding

1. Block is transformed using the DCT2. Perform edge detection3. Select pair of DCT coefficients from the sub-band

used using a Pseudo random permutation4. Quantize the selected coefficients using the

MPEG-2 algorithm5. Determine if the coefficient pair is suitable for

embeddingAvoid “Edge” and “Plain” blocks

6. Enforce a differential relationship between the coefficients in the pair to encode a “1” or a “0”

7. Inverse quantize the modified coefficients

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Busch Watermarking DCT CoefficientsBusch Watermarking DCT Coefficients

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7

Level 1

Level 2

Level 3

Public

Coefficients Used For Edge Detection

If the absolute value of one of the highlighted coefficients is greater than 39, the block is classified as an “edge” and not used.If the quantized value of one

of the coefficients in the selected band is zero the block is classified as a “plain” block

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VisibilityVisibility

“Edge” blocks, if modified, are highly visible in video and are to be avoided

“Plain” blocks are not so sensitive, so they can be used if care is exercised– In one of the bands randomly select a pair of coefficients and

randomly select one to be the “first” (DCT1) and another to the “second” (DCT2)

– To encode a “one” set DCT1 = (ABS(DCT1)+ ABS(DCT2))/2 + K, Preserving the sign(DCT1)

– To encode a “zero” set DCT1 = (ABS(DCT1)+ ABS(DCT2))/2 - K, Preserving the sign(DCT1)

– K is elected as a compromise between visibility and robustness to MPEG-2 compression

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ReferenceReference

C. Busch, W. Funk, and S. Wolthusen: “Digital Watermarking: From Concepts to Real-Time Video Applications”; IEEE Computer Graphics and Applications, 1999

Matlab OverviewMatlab Overview