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Chng 6 : Gii thut m phng

6.1 L

u

gii thu

t

Hnh 6.1 Lu gii thutqu trnh nhng watermark

nhgc

DWT

Watermark

RGB

YCbCr

Spxp

nh nhngwatermark

Y

H s t l

CbCr

Ccbngcon

mc 3

Lin ktRGB

Bngh s

Nhng

YCbCr

RGB

Spxp

K hiu& bng h

s

Y

IDWT

Lng tha

dion nhng

La chncc h s

nhng

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Mc tiu lun vn l vit chng trnh mphng qu trnh watermarking nh

s khai thc c tnh a phn gii ca bin i wavelets thc hin nhng v trchwatermark. V thc hin vi nh dng nh mu. Lun vn thc hin theo hng

qu trnh trch cn mt n ca nh gc tc watermarking bn m.

Trong lu gii thut nhng watermark, chui bit nhng l mt nh mu

kch thc m x n to ra mt chui bit nhng c m*n gi tr. nh gc s c bin

i sang min wavelet. Sau , N h s ln nht trong bng tn c chn nhng

s c cng vi watermark ( c nhn vi mnh nhng strength). D liu

sau khi cng s c bin i wavelets ngc v c lm trn gi tr theo nhdng pixel nh to ra nh sau watermarking.

Hnh 6.2Lu gii thutqu trnh trch watermark

Trong lu gii thut trch watermark, nh sau watermarking (c th b tn

cng hoc khng) c bin i sang min wavelets, xc nh li v tr ca N h s

nh nhng watermark

DWT

RGB YCbCr

Trch cch s gn

Watermarktrch

Y

CbCr

Cc bngcon mc 3

Index nhgc

di &h s t l

K hiu &bng h swatermark

Trch hs

watermark

Tch RGB

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ln nht trong bng tn c chn nhng ca nh gc, sau a qua b tr

trch ra watermark trong nh sau watermarking.

Qu trnh phn tch v khi phc wavelets c thc hin theo gii thutmatlab trn da trn m hnh bng lc hai knh.

Hnh 6.3Lu gii thut phn tch wavelets 1D a mc

Hnh 6.4Lu gii thut khiphc wavelets 1D a mc

Ly mu ln 2

Ly mu ln 2

H s xpx cAj Lc thng thp

khiphc Lo_R

Lc thng caokhiphc Hi_R

H s chitit cDj

Gi likch thc

H s xp xmc cAj-1

Lc thng thpphn tch Lo_D

Lc thng caophn tch Hi_D

Tn hiugc S

Ly mu xung 2

Ly mu xung 2

H s xp x cA1

H s chi tit cD1

Lc thng thpphn tch Lo_D

Lc thng caophn tch Hi_D

H s xpx cAj

Ly mu xung 2

L y m u xu ng 2

H s xp xmc j + 1 cAj+1

H s chi tit mcj + 1 cDj+1

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Vic thc hin phn tch v khi phc wavelets mt chiu (1D) c thc

hin nhhnh 6.3 v 6.4. qu trnh phn tch, tn hiu gc ln lt c a qua

b lc phn tch thng thp v thng cao. Tn hiu ra khi b lc ny c ly mu

xung to ra cc h s xp x cho n mc phn tch sau cng. Qu trnh khi

phc c thc hin ngc li. Cc h s xp x trc tin c ly mu ln, sau

c a qua cc b lc khi phc thp v cao. Tn hiu ra khi cc b lc ny

c a qua b gi li kch thc nhm to ra tn hiu khiphc sau cng c kch

thc bng vi kch thc ca tn hiu gc.

Qu trnh phn tch v khi phc wavelets hai chiu (2D) c th thc hin

da trn cc qu trnh phn tch v khi phc wavelets mt chiu (1D). Qu trnh

ny c dng cho d liu nh v c th hin hnh 6.5 v 6.6. Trc tin d

liu nh c thc hin theo hng, sau n cc ct v to ra bn bng tn khc

nhau mt mc phn tch no . l cc bng tn xp x, chi tit ngang chi tit

dc v chi tit cho.

Hnh 6.5Lu gii thut phn tch wavelets 2D a mc

Ghi ch : 2 1 : Ly mu xung theo ct : ch gi li ct chn

1 2 : Ly mu xung theo hng : ch gi li hng chn;

1 2

1 2

Lo_D

Hi_D

2 1Lo_D

1 2

1 2

Lo_D

Hi_D

2 1Lo_D

cAj

H s x p xcAj+1

(approximation)

H s chi titngang cDj+1(horizontal)

H s chi tit chocDj+1 (diagonal)

H s chi ti t dccDj+1 (vertical)

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Lo_D: B lc thng thp ca h wavelets

Hi_D : B lc thng cao ca h wavelets

Vic khi phc nh c th c thc hin bng cc bc sau. Trc tin

thc hin ly mu ln 2 ln cho tt c 4 bng con ti t l nh nht, v lc cc bng

con theo mi chiu. Sau chng ta ly tng bn bng con c lc c bng

con LL t l mn hn k tip. Qu trnh ny s c lp li cho ti khi nh c

khiphc hon ton.

Hnh 6.6Lu gii thut khiphc wavelets 2D a mc

6.2 Cc bc thc hin

Da vo lu gii thut, vit chng trnh m phng nhng v trch

watermark bng cng c m phng matlab 2007 vi i tng nhng l nh mu.

- Kho st qu trnh watermarking trong iu kin l tng (ngha l chab tn cng). Mc ch l kim tra tnh ng n ca gii thut, tm ra

mi quan h gia thng s cng watermark nhng vi kh nng cm

th watermark xc nh phm vi thch hp ca cng watermark

trong qu trnh nhng.

2 1 Lo_R

2 1 Hi_R

1 2 Lo_R

2 1 Lo_R

2 1 Hi_R

1 2 Hi_R

Gi likch thc

cAj+1

cDj+1

(horizontal)

cDj+1

(vertical)

cDj+1

(diagonal)

ct

ct

ct

ct

cAj

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- Kho st tc ng ca cc tn cng. Thc hin mt s tn cng, kho sttnh bn vng ca h thng trc cc loi tn cng

Thc hin watermarking trong min DWT lm cho h thng trnn mnhm v bn vng hn khi so vi min DCT truyn thng trong khi vn m bo yu

cu v mc cm th, c bit l trong cc tn cng nn JPEG2000, lc trung

bnh, lc Gaussian, lc sc nt v co dn nh. Xt v mt thi gian cng nh

phc tp th vic thc hin watermarking trong min DWT l hon ton kh thi.

iu ny m ra mt hng nghin cu dng php bin i wavelets trong

watermarking cho cc ng dng i hi thi gian thc nhiu khin v chng sao

chp hay xc nhn ly du tay. Ngoi ra, t kt qu ny, c th tin hnh thc hin

watermarking cho chui d liu video vi mt siu chnh hp l t kt qu

tt hn. Xa hn na, c th kt hp thc hin vi d liu audio watermarking

cho d liu media.