4 Mot So Thuat Toan Watermaking

7/30/2019 4 Mot So Thuat Toan Watermaking

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Chng IV: Mt sThut ton Watermarking

Gn y, phn ng thut ton watermarking sc pht trin nhm mc

ch bo v bn quyn nh s v xc minh tnh trng nguyn vn d liu. Hu ht

cc thut ton watermarking chuyn i nh gc sang mt min lm thun tin cho

vic nhng thng tin watermark nhm bo m tnh bn vng v khng nhn thy.

Nhng phng php trc th vn dng php bin i cosin ri rc (DCT) nhng

nhng h s quan trng cm nhn c trong ph tn s thp, tiu chun nn JPEG

cng da vo DCT. Tuy nhin, nhng iu kin cn mi nh l vic truyn tc

bit thp v tin dn, c tnh t l v m ha ROI (region-of-interest) i hi vicm ha nh linh hot v hiu qu hn. Tiu chun nn nh JPEG2000 da trn php

bin i wavelet ri rc (DWT) c nhiu ci tin v cho t l nn cao hn. V th

lun vn ny nghin cu s watermarking trong min bin i Wavelet.

4.1 Phng php watermarking trong min khng gian nh (spatial domain)

Watermarking trong min khng gian tn hiu c kho st bng cch ri rc

trc tip. Cc gi tr ri rc ca im nh gi l min bin sc lp t nhin. Sau

tm cch nhng thng tin vo nh bng cch thay i cc gi trim nh sao

cho khng lm nh hng nhiu n cht lng nh v m bo s bn vng ca

thng tin nhng trc nhng tn cng c th c i vi bc nh nhng. C hai

phng php in hnh l phng php tch bit c trng s t quan trng nht (LSB-

Least Significant Bit) v phng php s dng chui gi ngu nhin.

4.1.1 Qu trnh chn watermark vo hnh nh

Mc ch:

a mt on thng ip N bit (Watermark) vo image A.

Cch thc hin:


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- Chia nh A (nh gc) thnh lm N khi c chiu di bng nhau hoc gn

bng nhau.

- Trn mi khi: ly ngu nhin 1 bit c trng s nh nht ca 1 im nhthuc khi (c th chn cnh bit c trng s nh nht ca byte u tin, tuy

nhin lm theo cch ny th watermark d b ph hy hn).

- Trn mi khi thay th 1 bit c chn bng 1 bit trong watermark W s

thu c mt hnh nh A v mt kho key, kho ny cho bit v tr ca bit trong

khi i c thay th.

Nhn xt:

V dng bit c trng s nh nht cha message (watermark) nn trong cc

tc v x l nh thng thng ngi ta c th b qua bit ny m cht lng ca nh

khng b suy gim. Do cch a watermark vo nh theo cch ny s khng bn

vng trc cc tn cng.

4.1.2 Qu trnh pht hin watermark:

Mc ch:

Pht hin xem nh A c cha watermark hay khng?

Cch thc hin:

- Gi tr vo: A, A, v key.

- Da vo key ta ly c cc bit b thay i trong gii thut nhng trn.

- So snh A v A ch khc nhau cc v tr quy nh trong cc bit hay

khng? Nu ng th A cha watermark t A, ta c th thu c watermar W bng

cch ly li cc bit thay i trn.

Nhn xt:

Bi v so snh A v A i hi phi ging nhau tt c cc v tr cn li nn

khi nh A b nhiu hoc b thay i do cc hnh ng thng thng nh ct, xoay


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nh th gii thut trn khng pht hin c. Trong thc t th khi hin thc gii

thut ny ngi ta khng yu cu phi so snh chnh xc, m c mt sai s cho

php, nu kt qu ca qu trnh so snh A v A nh hn sai s cho php ny th

xem nh A c sinh ra t A.

4.2 Phng php watermarking dng bin i DCT

K thut watermarking dng php bin i DCT thng chia nh gc thnh

cc khi, thc hin php bin i DCT vi tng khi nh gc c min tn s

thp, min tn s gia v min tn s cao. a s k thut watermarking n bn

vng s chn min tn s gia ca mi khi nhng watermark theo mt h s k

no gi l h s tng quan gia cht lng nh sau khi nhng (tnh n ca

watermark v bn vng ca watermark)

V dn gin qu trnh watermarking s dng bin i Cosin ri rc (DCT)

vi i tng nh nh sau:

Thc hin bin i DCT i vi nh cha m c i din bi khi th

nht (8x8 pixel) ca bc nh rng cy nh trn hnh 4.1.

Hnh 4.1: Khi 8x8u tin ca nh Rng cy

Khi B1


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Khi c cho bi:

0.7232 0.8245 0.6599 0.7232 0.6003 0.6122 0.6122 0.5880

0.7745 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232 0.72320.7745 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232

0.7025 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232

B1 = 0.7745 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232

0.7025 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232

0.7025 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232

0.7025 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232 0.7232

Bin i DCT khi B1c kt qu l:

Lu : phn ln nng lng DCT ca B1 c nn ti gi tr DC (h s

DC=5.7656).

Watermark l mt s gi ngu nhin c pht sinh bng cch dng b to

s ngu nhin khi u t gi tr ngun (kha), c cho bi:

5.7656 0.1162 -0.0379 0.0161 -0.0093 -0.0032 -0.0472 -0.0070

-0.0526 0.1157 0.0645 0.0104 -0.0137 -0.0114 -0.0415 -0.0336

-0.0354 0.0739 -0.0136 -0.0410 -0.0081 -0.0187 -0.0871 0.0063

-0.0953 0.0436 0.0379 -0.0090 -0.0394 0.0182 -0.0031 -0.0589

DCT (B1) = -0.1066 0.0500 0.0034 -0.0355 -0.0093 0.0147 0.0526 -0.0278

-0.0790 -0.0064 0.0088 0.0240 -0.0200 -0.0361 -0.0586 -0.0731

-0.0422 0.0366 -0.0460 -0.0150 0.0518 0.0141 0.0105 -0.0980

0.0025 0.0697 0.0327 -0.0140 0.0286 -0.0084 -0.0422 0.0329

1.6505 0.2759 -0.8579 -1.6130 -1.0693 0.2259 -0.4570 0.7167

0.7922 - 0.6320 0.8350 -0.3888 0.4993 0.2174 -1.6095 -0.92690.7319 0.7000 1.6191 -0.0870 0.7859 0.1870 -0.3633 2.5061

0.9424 0.8966 -0.0246 -1.4165 0.5422 0.1539 -1.1958 0.0374

W = 0.2059 1.8204 0.5224 -0.9099 -1.6061 -0.7764 -0.8054 -1.0894

-0.1303 -0.3008 1.6732 -1.1281 -0.3946 0.8294 -0.0007 -0.7952

0.0509 -1.7409 1.1233 0.3541 0.1994 -0.0855 0.1278 -0.6312

-0.1033 -1.7087 0.5532 0.0268 2.5359 1.7004 -0.6811 - 0.7771


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Bin i DCT trn W, c kt qu l:

Hnh 4.2: S khi qu trnh to watermark

B1 c watermark vi W nh biu din trong s khi hnh 4.2, cn

c theo:

fwffW

+= (4.1)

Trong f l h s DCT ca tn hiu cha (B1), w l h s DCT ca tn hiu

watermark (W) v l nng lng watermarking c ly n 0.1 ( = 0.1). Gi tr

DC ca tn hiu cha th khng c thay i mc ch l lm gim s mo dng

ca nh c watermark. Do vy, gi tr DC sc gi li, khng b nhng.

0.2390 1.5861 0.1714 0.7187 -0.3163 -1.0925 2.6675 1.31640.1255 0.8694 2.8606 -0.2411 0.6162 -1.1665 -0.1335 -0.8266

0.0217 -1.4093 -1.3448 1.3837 1.3513 1.0022 0.8743 0.3735

-1.7482 0.8337 1.5394 -0.0076 -1.7946 1.1027 -0.4434 -0.5771

DCT (W) = -0.7653 0.5313 0.9799 1.2930 -0.0309 -0.9858 -0.9079 -0.8152

0.4222 -0.9041 1.2626 -0.0979 0.6200 0.1858 -0.1021 0.1452

1.4724 -1.1271 1.7449 -0.2921 - 0.3144 -0.7244 0.4119 0.0535

0.4453 0.0380 0.9942 -1.5084 0.0656 0.4169 -0.7046 - 0.5278

Bin itn s(DCT)

B m ho = 0.1

B toWatermark

Bin i tns ngc(IDCT)

+

key

Bin itn s(DCT)

nh nhngwatermark

nh gc


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Phng trnh (4.1) c thc vit li dng ma trn nh sau:

Trong , B1w l tn hiu c watermark ca B1. Kt qu sau khi p dng

hm trn nh sau:

Ch gi tr DC ca DCT (B1w) ging gi tr DC ca DCT (B1). to nh

c watermark, thc hin bin i DCT ngc ta c kt qu sau:

Nhn xt:

- D dng so snh B1w v B1 v nhn thy s thay i rt nh do watermark.

- Phng php bn vng di s thay i khc nhau ca nh nn k thut

ny p dng trong thit b xc nhn, chng li nn JPEG.

- Tuy nhin cn c nh gc khiphc watermark.

DCT (B1) + . DCT (W). DCT (B1), vi mi h s, tr gi tr DC

DCT (B1w)= (4.2)DCT (B1) ch vi gi tr DC

5.7656 0.1346 -0.0386 0.0172 -0.0090 -0.0028 -0.0598 -0.0079

-0.0532 0.1258 0.0830 0.0101 -0.0145 -0.0101 -0.0409 -0.0308

-0.0355 0.0635 -0.0117 -0.0467 -0.0092 -0.0206 -0.0947 0.0066-0.0786 0.0472 0.0438 -0.0090 -0.0323 0.0202 -0.0029 -0.0555

DCT(B1w) = -0.0984 0.0527 0.0037 -0.0400 -0.0092 0.0132 0.0478 -0.0255

-0.0823 -0.0058 0.0099 0.0238 -0.0212 -0.0368 -0.0580 -0.0742

-0.0485 0.0325 -0.0494 -0.0146 0.0502 0.0131 0.0109 -0.0985

0.0026 0.0700 0.0360 -0.0119 0.0288 -0.0088 -0.0392 0.0312

0.7331 0.8361 0.6609 0.7228 0.5991 0.6026 0.6175 0.5922

0.7818 0.7809 0.7735 0.7011 0.7712 0.6955 0.7755 0.6998

0.7734 0.7746 0.6973 0.7682 0.7663 0.7002 0.6956 0.6920

0.7064 0.7093 0.7045 0.7037 0.7013 0.7692 0.6986 0.6933

B1w = 0.7872 0.7100 0.7789 0.7081 0.7067 0.7012 0.7013 0.6996

0.7051 0.7032 0.7026 0.7801 0.7078 0.7741 0.7015 0.6978

0.7017 0.7765 0.7002 0.7067 0.7765 0.7026 0.7736 0.6992


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4.3 Phng php watermarking tri ph

Nhiu k thut watermarking hp nht nhiu tng ca truyn thng tri

ph [35,47] nhng v trch m hnh nhiu gi ngu nhin thm vo.

Trong truyn thng tri ph, mt tn hiu bng hp c tri qua mt bng

tn rng ca tn s. iu ny c th c thc hin bng cch iu ch tn hiu

bng hp (thng tin watermark) cng vi tn hiu bng rng chng hn nh nhiu

Gaussian. Tn hiu watermark tri ra c xem nh l nhiu c mt trong tn

hiu nh v v th kh m pht hin.

Mt khc, phng php ny c tr ngi l bn thn tn hiu nh phi c

xem nh nhiu, iu ny lm cho vicpht hin watermarkkh khn. pht hin

ra s c mt ca watermark mt cch ng tin, dng nh nhiu h s phi tng

quan hn. iu ny lm gim tnh bn vng v dung lng ca thut ton.

4.4 Phng php watermarking dng bin i Wavelet

4.4.1 L do dng phn tch wavelet

V sao li chn tip cn bng php bin i wavelet. Ta nhn thy rng ccc trng trong min bin i ny l kh ph hp vi mt n v n tp trung c

trong min thi gian v min tn s. Bn cnh bin i waveletph hp vi m

hnh a knh ca h thng nhn ca con ngi (HVS) v th tht s c th t mt

s gii hn vo cc h s wavelet sp xp chng di mc HVS ch sai khc

3JND, m mt ngi c th bt u cm nhn s thay i trong nh.

Ngoi ra, bin i wavelet l mt phn ca chun nn da trn JPEG-2000 v

th k thut da trn wavelet thc hin d dng v ti u hn bao gm c vicbov bn quyn vo trong cc m nn ca n.


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4.4.2 Watermarking dng phn tch wavelet

K thut watermarking c bn s dng php bin i DWT thng phn tch

nh gc thnh 4 bng tn s khc nhau gm: tn s cao, tn s gia v tn s thp(k hiu l : LL1, HL1, LH1, HH1) bng cch sp xp cc b lc bng con. to

thm c cc h s wavelet, bng con LL1 li tip tc c phn tch tip. Qu

trnh ny c lp li cho n khi c c kt qu mong mun nhm ph hp vi

tng ng dng. Sau nhng thng tin watermark vo mt hoc mt s wavelet

bng con vi cc h s tng quan khc nhau. nh cha watermark sau c

th qua cc php bin i nh thng thng ri tm li watermark gc

[35,21,8,23,29,22,43].

Hnh 4.3 m t s tng qut ca thut ton watermarking dng bin i

wavelet.

Hnh 4.3 : S watermarking tng qutdng phn tch wavelets

Trc tin, phn tch a phn gii v th bc c lu vo b pht hin ca

my tnh. Sau n c lm trong sut nhs dng cc c trng ca h thng

nh gc nh nhng watermark

watermark

Trch

watermark

1. Nhng

watermark

5.So snh

2. M ho

3. Truyn

4. Gii m


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nhn. Lu cn cn nhc gia tnh trong sut ca nh sau khi nhng v tnh mnh

m ca phng php. Cui cng dng bin i wavelets ph hp vi chun nn

nh, s watermarking c th d dng thch ng vi chun nn JPEG-2000 da

trn cswavelet.

Cch lm n gin l cng cc m ngu nhin gi c trng s vo cc h s

ln ti cc bng tn s cao v gia ca bin i wavelet ri rc ca nh.

Cch thc hin:

- Phn tch nh thnh 10 bng con dng h wavelets Haar.

Trong hnh 4.4, nh gc Lena c phn tch lm 3 mc vi 10 bng con.

Mi mc c thng tin bng tn c th chng hn nhl LL, LH, HL v HH. Bng

tn thp nht nm trn cng bn tri, v bng tn tn s cao di cng bnphi.

Hnh 4.4 : Ktquphn tch DWTnh[

LL3

HL2

HH2LH2

HL1

HH1LH1

HL3

LH3 HH3


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Qu trnh nhng

- Tip theo cng mt chui ngu nhin gi N (thng dng phn b Gauss c

trungbnh bng khng v phng sai n v) vo cc h s ca cc bng tn s caov bng tn s gia (ngha l tt c cc bng tn thp nhtb loi tr, nm gc tri

bn trn ca hnh 4.4). Phn b chun ha c dng v n kh mnh m vi cc

loi tn cng kt cu. sp xp trng s watermarkvo cc h s wavelet c bin

ln, ta dng mt trong hai quan h theo hai phng trnh sau i vi cc h s

ca nh gc y v y, ni cha watermark .

[m,n] = y[m,n] + . (y[m,n])2 N[m,n] ( 4.3)

hoc

[m,n] = y[m,n] + . abs(y[m,n]) N[m,n] (4.4)

Gia (4.3) v (4.4) v mt ton hc khc nhau nhng li c cng mc ch l

t nhiu trng s watermarkc cng vo cc h s wavelet c gi tr cao. Tham

s dng iu khin mc watermark, cch tt nht chn la l phi dung

ha gia tnh mnh m v dung lng. Cui dng bin i wavelet ngc hai chiu

to li nh nhng watermark y.

Qu trnh trch

Ti u cui ca knh truyn, mt b gii m c dng trch thng tin

watermark t nh thu c. Da trn nh watermark xut, thut ton pht hin

watermark bng cch so snh cc h s DWT ca nh thu c so vi DWT ca

nh gc (khng nhng watermark). Bi ton gm vic ly kha mt t vo trong

bng cch tnh tng quan cc mc phn gii u tin (ngha l cc h s tn s cao

nht). Watermarkcpht hin nu c nh tng quan ng vi du hiu dng.Nu khng, b gii m thc hin tip mc phn gii th hai (ngha l hnh vung

y bn tri ca cu trc pyramic hnh 4.6) mc ch tm nh. Nu c mt

nh th watermarkc gi l b pht hin nu khng c tip tc cho ti mc phn

gii th ba v c th cho n mc cui cng l th chn. K thut ny chophppht


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hin watermark tt thm ch cphnb sa, gi mcpht hin sai trng thi

cc tiu v tm kim du hiu ring xuyn qua tng bcpht hin xc nhn gi

tr dng gi l b pht hin. Mc ch cc bc ca b pht hin nhm bo m

cc i gi tr trch c trong b pht hin vi cc key ring, cc tiu s gi tr

dngpht hin sai.

4.4.3 Watermarking nh s dng bin i Wavelets

Watermarking nh mu dng bin i wavelets nhm giu thng tin vo

trong nh gc. Trong phng php ny nh gc l nh mu, u tin c tch

thnh 3 knh mu RGB, sau tng knh c phn tch thnh cc h s wavelet.

Vi nh watermark, cc knh RGB c lin kt thnh nh knh n 3 chiu v

cng c phn tch thnh c h s wavelet vi cng t l phn tch. Cc h s

watermarkc cng vo trong cc h s ca nh gc tng ng vi cc bng con.

K thut cng thch nghi dng gn iu khin kh nng khng th nhn thy

c v bn vng.

u tin lun vn tin hnh nhng watermarkvo bng tn xp x ca mc

phn tch wavelet th ba (dng hm wavelet haar) n gin. Sau lun vn s

ln lt thc hin cc kho st cc bng tn khc nhau, cc mc phn tch khc

nhau, v cc hm wavelet khc nhau sau rt ra kt lun cn nhng watermark

u hiu qu nht m bo dung ha c tnh khng nhn thy v t c

mnh m cao.

Hnh 4.5 Trnhby qu trnh thc hin nhng watermark


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4.4.3.1 Qu trnh nhng Watermark

Hnh 4.5: S thc hin nhng watermark

4.4.3.2 Qu trnh trch watermark

Ti u cui ca knh truyn, mt b gii m c dng trch thng tin

watermark t nh thu c. Da trn nh watermark xut, thut ton pht hin

nh gc

DWT

DWT

Sp xp li

Nhng

IDWT

nh sau nhng watermark

nh watermark


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watermark bng cch so snh cc h s DWT ca nh thu c so vi DWT ca

nh gc (khng watermark).

Hnh 4.6 S thc hin trch watermark

4.4.3.3 Kim tra tnh bn vng

Ch tp trung vo kt qu cc tn cng bng cc ton t x l nh n gin.

Bng cch ny ta c th chc chn rng h thng ny c th dng truyn nh.

nh gc

DWT

DWT

Sp xp li

Cc bng congn

watermark

IDWT

nh nhng watermark

Watermarked

DWT


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Phng php cn c kim tra bng cc tn cng sau :

Tn cng nn nh : JPEG, JPEG2000 Lc: nhiu loi b lc khc nhau c dng. V d nhcc b lc trung

bnh (average), trung v (median), lc gauss v cc b lc khng nhn

(unsharp filters).

Bin i hnh hc: ct, xoay, thay i kch thc.

Hnh 4.7 S m t nh watermarked nhn c trong thc t

Thut ton watermarking c thc hin bng MATLAB 2007 s dng cng

c phn tch nh v wavelets. Matlab rt mnh m trong vic kim tra v ti u ha

thut ton. Gip trnh vit cc m cho wavelets khi chng c thc hin ti u

bng cng c Wavelet.

Tn cngNhng

nh gc nh nhng watermarknh nhng

watermark

sau khi b tn cng

JPEG

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4 Mot So Thuat Toan Watermaking