Lecture25(2)

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Digital

Watermarking

Lecture notes taken from the

Web

faculty.kfupm.edu.sa/EE/samara/ WAtermarking %20 Lecture%202.ppt

Author Unknown

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Introduction

• Relation to Cryptography

– Cryptography is

• Reversibility (no evidence

• !stablished

– Watermarking ("##$s

• %on&reversible (noise

– Information 'iding• Covert communication channel (steganography

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Digital Watermarking

edia

• )ideo

• *udio

• Images – +ur discussion ,ill focus on this-

Watermarking

*lgorithm

Watermarked

Image

+riginal

Image

Watermark.lock Diagram

of image ,atermarking

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*pplications

• Copyright – /he ob0ective is to permanently and unalterably mark the image

so that the credit or assignment is beyond dispute-

• Digital Rights

– * file may only be used by users ,ith a license that matches the,atermarked signature-

• Information 'iding – 1oil counterfeiters

• Revision 'istory – /amper detection

• eta&tagging – 2tore key,ords3 descriptions3 time along ,ith images-

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Criteria

• ain Criteria

– Capacity

– 4ayload

– Computational Comple5ity

– /ransparency

– RobustnessRe6uire optimum relationship

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Capacity

• /he ability to detect ,atermarks ,ith a lo,

probability of error as the number of

,atermarks in a single image increases-

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4ayload

• /he amount of information that can be

legitimately stored ,ithin a data stream

– Dependent on host medium

– 74!8 e5ample

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Computational Comple5ity

• Difficulty in process of ,atermark

e5traction

– Realtime9

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/ransparency

• /ransparency refers to the perceptual

6uality of the data being protected-

– Watermark should be invisible over all image

types as ,ell as local image characteristics-

• %eed to consider perceptually insignificant

portion of host image for insertion for

ma5imum transparency

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Robustness

• Resistance to attacks on the ,atermark – *ttack – an operation performed on the image that

compromises the ,atermark

– *ctive3 4assive3 Collusion3 1orgery – .lind vs- %onblind

• :se of non&robust ,atermarks

– eg- tamper detection

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*pproaches and Implementation

• /,o /ypes of !ncoding

– 2patial ,atermarking (spatial domain

– 2pectral ,atermarking (fre6uency&domain

• any types due to variety of transforms

• *d0ustments made in fre6uency domain

• ore robust

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2patial&Domain Implementation

• Lo,&level !ncoding

• :se of Image *nalysis +perations – eg- !dge Detection;Color 2eparation

• Cons – !asily *ttacked (Cropping

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1re6uency&Domain Implementation

• *lgorithm

– Decomposition of image

– *ddition of Watermark

• 4ossibly encoded;encrypted

– Re&composition of Image

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(Discrete Cosine /ransform

• Discrete Cosine /ransform (DC/

– :sed in today

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(Wavelet /ransform

• Wavelet /ransform

– .ased on 2hort /ime 1ourier /ransform

(2/1/

– .ecoming more common in compression

techni6ues

• .etter model of 'uman )isual 2ystem than DC/

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!5amples of Wavelets

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1re6uency&Domain Implementation(Common Wavelet /ransform *lgorithm & Decomposition

1ilter .ank Decomposition ("$ .ands

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1re6uency&Domain Implementation(Wavelet /ransform *lgorithm & +vervie,

Watermarked Image

!ncodedWatermark

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(Corte5 /ransform

• Corte5 /ransform

– Recent

– imics human visual system

• Corresponds to kno,n structure of human eye

– 'as its o,n disadvantages

• Computational comple5ity – re6uires much more

data>

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+ther Issues

• 7ust %oticeable Difference (7%D

– /hreshold based on 'uman )isual 2ystem

• *d0ustment in 1re6uency

• *d0ustments in Intensity

– Important impact on transparency

• 2patial ad0ustment of 1re6uency&Domain

Watermark

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2pread 2pectrum

• :sed to fulfill transparency criterion

• /he ,atermark in is based on spread spectrum

communications

– Delivers narro,band data through a noisy channel3 bymodulating each data symbol ,ith a ,ideband (but

very lo, amplitude signal-

– /he data is a single bit – a yes or no decision on

,hether the given ,atermark is present- – /he channel is the image data itself

– /he ,ideband signal is the ,atermark-

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Color Images

• 2cheme nearly identical to grayscale

– R;8;. channels

• !ach color plane treated as a separate image

– Luminance;Chrominance channels

• Luminance ? intensity

• Chrominance ? color

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Resources

• ftp@;;skynet-ecn-purdue-edu;pub;dist;delp;,atermark&proceedings;paper-pdf

• http@;;,,,-cosy-sbg-ac-at;Apmeer,;Watermarking;

• http@;;,,,-cosy-sbg-ac-at;Apmeer,;Watermarking;aster/hesis;

• http@;;,,,-eso-org;pro0ects;esomidas;doc;user;#B%+);volb;node$B-html

• http@;;,,,-00tc-com;2teganography;

• http@;;,,,-math,orks-com;matlabcentral;files;$B;digitalEF$,atermarking-pdf • ihcak3 ehmet Givanc- HInformation 'iding Codes and /heir *pplications to Images

and *udio3 4hD /hesis- F$$F-

Documents

Lecture25(2)