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Optimization of Watermarking Performances using Error

Correcting Codes and Repetition S.Zinger, Z.Jin, B.Sankur*, H. Maître

Ecole Nationale Supérieure des Télécommunications

46, rue Barrault, 75634 Paris Cedex 13, France

{zinger, jin, maitre}@tsi.enst.fr

* Boğaziçi University

80815 Bebek - Istanbul, Turkey

sankur@boun.edu.tr

S.Zinger, Z.Jin, B.Sankur*, H. Maître

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The goal

to explore applying coding methods

for watermarking purposes

robustnessthe length of the

signaturethe length of the

coded word

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The constraints:

• imperceptibility

• robustness

• capacityw ~ 10 - 100 bits

c ~ 200 - 500 bits

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Capacity is the maximum amount of bits which can be hidden in an image

• Ramkumar, 1998• Servetto, 1998• Barni, 1999• Marvel, 1999• Lin, 2001• Sugihara, 2001

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Coding methods• Repetition• ECC BCH codes• Hybrid coding

original watermark

binary symmetric channel

extracted watermark

?

attacks

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Repetition

Bit error probability after repetitions r

,11

2

r

ri

irbsc

ibsc

irrep ppCP

wreprepsig PP 11,

Probability of error for a signature of bitsw

cwr

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BCH codes

• Standard BCH codes ,

• BCH codes by parts

• BCH codes with subtraction

n

ti

inbsc

ibsc

inBCHsig ppCP

1, )1(

,cn tkn ,, wk

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Examples of BCH codes

Capacity bits, payload bits500c 32w

Standard BCH codes

code (255,37,45)

BCH codes by parts

(127,15,27) (127,15,27) (127,15,27)

BCH codes with subtraction

(500,38,93)

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Hybrid coding

• BCH coding after repetition

• repetition after BCH

1

1, 1

n

repirep

n

ti

inhybridsig PPCP

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A comparison of performancesChannel error rate is 5%, capacity is 350 bits

210

3610Hybrid coding

Repetition

BCH with subtraction

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Average of performances 500200 c

Channel error rate is 5%

Hybrid coding

Repetition

BCH with subtraction

210

2510

for capacity

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Average of performances

500200 cChannel error rate is 15%

Hybrid coding

for capacity

Repetition

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Average of performances

500200 cChannel error rate is 30%

Hybrid coding

Repetition

for capacity

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The best coding strategy,10 2sigP 400c

Repetition

Shannon capacity

Hybrid coding BCH with

subtraction

for

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Connection between channel error rate and JPEG compression rate

-0,1

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0 20 40 60

JPEG compression rate

be

r