nhan dang va xu li anh

8/3/2019 Nhan Dang Va Xu Li Anh

1/17

Bi ging mn hc Nhn Dng v X L nh

BI 1TNG QUAN V X L NH

1. Gii thiu chungNhn dng v x l nh l mt trong nhng lnh vc c nhiu ng dng trong

thc tin nh: h thng tin a l (GIS Geographic Information System), qun s,y hc.

C th, x l nh s c rt nhiu ng dng nh:- Lm ni cc nh trong y hc.- Khi phc li nh do tc ng ca kh quyn trong thin vn hc.- Chuyn ti, nn nh khi truyn i xa hoc lu tr.

2. Cc giai on ca qu trnh x l nh- Nhn dng v X l nh bao gm 2 giai on chnh:

- Giai on bin i nh (Image Transformation) hay lm p nh(Image Enhancement): trong giai on ny, nh ca i tng trong t nhin cthu li thnh nh s (s ha lu tr v x l trong my tnh). Sau nh c

bin i nng cao cht lng nh nhm thu c nhiu thng tin hn, c thquan st bng mt.- Giai on nhn dng mu (Patten Recognition): h thng s x l

a ra cc c trng ca nh hay cc i tng trong nh. Sau h thng snh gi ni dung nh hoc nhn bit cc mu trong nh.

3. Mt s khi nim lin quan3.1. Phn t nh

- nh trong t nhin l nhng tn hiu lin tc v khng gian v gi tr sng. c th lu tr v biu din nh bng my tnh, con ngi

phi tin hnh bin i cc tn hiu lin tc thnh mt s hu hncc tn hiu ri rc thng qu qu trnh lng t ha v ly mu thnh

phn gi tr sng.- Mt phn t nh (Picture Element) l mt gi tr biu din cho mc

xm hay cng nh ti mt v tr sau khi bin i nh thnh mts hu hn cc tn hiu ri rc.

3.2. Mc xm- L kt qu ca s bin i tng ng gi tr sng ca mt im nh vimt gi tr s nguyn dng. Ty thuc vo s gi tr biu din mc xm mmi im nh s c biu din trn 1, 4, 8, 24 hay 32 bit. S lng bit biu

din mc xm cng ln th cht lng nh cng cao nhng s tn dung lngb nh nhiu hn lu tr v cn mt h thng mnh hn x l.3.3. nh

L B Dng Khoa Cng ngh Thng tin - Trng i Hc Hng Hi Vit Nam

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- L mt tp hp hu hn cc im nh k nhau. nh thng c biu dinbng mt ma trn hai chiu, mi phn t ca ma trn tng ng vi mt imnh.- nh nh phn (en trng): l nh c gi tr mc xm ca cc im nh c

biu din bng 1 bit (gi tr 0 hoc 1).V d v biu din nh nh phn:

0 1 1 0

1 1 1 0

0 0 1 1

0 1 1 1

- nh xm: gi tr mc xm ca cc im nh c biu din bng 8 bit (gi

tr t 0 n 255).V d v biu din nh xm:

0 5 12 0

15 94 21 0

0 0 156

9

0 11 245

12

- nh mu: thng thng, nh mu c to nn t 3 nh xm i vi munn (RED), xanh l cy (GREEN), xanh lam (BLUE). Tt c cc mutrong t nhiu u c th c tng hp t 3 thnh phn mu trn theo cc tl khc nhau.V d v biu din nh mu:Ma trn biu din mc xm ca thnh phn RED:

0 7 11 0

115 94 20 0

0 0 15 16

0 11 225

12

Ma trn biu din mc xm ca thnh phn GREEN:

0 1 121

0

14 9 21 0


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0

0 0 115

16

0 11 22 2Ma trn biu din mc xm ca thnh phn BLUE:

0 17 21

0

135

93 50

0

0 0 15

67

0 11 25

19

4. Mt s nh dng nh hin nay4.1. nh BMP (Bitmap)

- L nh c m t bi mt ma trn cc gi tr s xc nh mu vbng mu ca cc im nh tng ng khi hin th. u im ca nh Bitmapl tc v v tc x l nhanh. Nhc im ca n l kch thc rt ln.

4.2. nh JPEG (Joint Photographic Experts Group)- y l mt nh dng nh c h tr bi nhiu trnh duyt web. nh

JPEG c pht trin nn dung lng v lu tr nh chp, v c sdng tt nht cho ha c nhiu mu sc, v d nh l nh chp c scan.File nh JPEG l nh Bitmap c nn li.4.3. nh GIF (Graphics Interchange Format)

- nh GIF c pht trin dnh cho nhng nh c tnh cht thay i.N c s dng tt nht cho ha c t mu, v d nh l nh hot hnh

hoc l nhng bc v vi nhiu ng thng. File nh GIF l nhng nhBitmap c nn li.- C hai s khc nhau c bn gia nh GIF v nh JPEG:

+ nh GIF nn li theo cch gi nguyn ton b d liu nh trong khinh JPEG nn li nhng lm mt mt s d liu trong nh.+ nh GIF b gii hn bi s mu nhiu nht l 256 trong khi nhJPEG khng gii hn s mu m chng s dng.

4.4. nh WMF (Windows Metafiles)- L mt tp hp cc lnh GDI dng m t nh v ni dung nh. C

hai u im khi s dng nh WMF: kch thc file WMF nh v t ph thucvo thit b hin th hn so vi nh Bitmap.


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BI 2X L NH NH PHN

1. L thuyt v nh nh phn1.1. Khi nim

- Mt nh c xem l nh nh phn (nh en trng) nu cc im nhca n ch nhn gi tr l 0 hoc 1 (tng ng vi mu en hoc trng).Do mi gi tr im nh c biu din bng 1 bit nn kch thc filenh rt nh.- Ta k hiu: J l tp cc im nh c gi tr bng 1

J l tp hp cc im nh c gi tr 0 (im nn).1.2. K thut phn ngng

- Dng chuyn i nh a cp xm sang nh nh phn- Vi mt gi tr cho trc, gi tr ca im nh s c gn bng 1nu mc xm ca n >= , gn bng 0 nu mc xm < .- K thut ny lm cho tnh cht mu lin tc ca nh b gin onnhng c hiu qu trong vic th hin cc loi nh c ng nt nhvn bn, vn tay- Ci t:

+ D liu vo: ma trn I kch thc mxn biu din mc xm ca

cc im nh. Gi tr ngng .+ D liu ra: ma trn I c bin i mc xm.+ M t thut ton:

for x=1 to mfor y=1 to nif I(x,y)>= then I(x,y)=1else I(x,y)=0

- V d:

nh gc =9 nh u ra

0 8 5 0 0 0


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9 2 30

1 0 1

8 12

40

0 1 1

1.3. K thut Dithering- S dng mt ma trn cng kch thc cho trc bin i nh.- Nu gi tr mc xm ca im nh gc ln hn gi tr ca phn ttng ng trong ma trn Dithering th mc xm u ra s c gn

bng 1 v ngc li.- Ci t:

+ D liu vo: ma trn I kch thc [mxn] biu din mc xmca cc im nh. Ma trn Dithering kch thc [mxn].

+ D liu ra: ma trn I c bin i mc xm.+ M t thut ton:for x=1 to mfor y=1 to nif I(x,y)> Dithering(x,y) then I(x,y)=1else I(x,y)=0

- V d

nh gc Ma trn D nh u ra

1 7 9 0 8 5 1 0 1

6 12

45

9 2 30

0 1 1

14

18

13

8 12

40

1 1 0

2. im k - tp im lin thng i tng nh2.1. im k

Cho trc mt im nh I(x,y), khi :- Cc im nh I(x-1,y), I(x+1,y), I(x,y-1), I(x,y+1) c gi l cc

im k 4 ca I(x,y).- Cc im nh I(x-1,y-1), I(x+1,y-1), I(x-1,y+1), I(x+1,y+1) v cc

im k 4 c gi l cc im k 8 ca I(x,y).- Tng ng vi cc im k 8, ta c mt n 8 hng xc nh cc

im k 8 :3 2 1


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4 P 0

5 6 7

Tng ng vi cc hng nh sau:

2.2. Tp im lin thng- Hai im nh P1 v P2 J c gi l lin thng 4(hoc 8) trong J nu tn

ti tp cc im {(x0,y0), (x1,y1), , (xn,yn)} sao cho:+ P1 = (x0,y0)+ P2 = (xn,yn)+ V(xk,yk) v (xk+1,yk+1) J th (xk+1,yk+1) l k 4(hoc 8) ca (xk,yk)vi k= [0..n-1]

(tp cc im {(x0,y0), (x1,y1), , (xn,yn)} c gi l ng i).

- Mt tp im c gi l lin thng nu vi hai im bt k trong tp hp u lin thng (4 hoc 8).

2.3. i tng nh- L mt tp hp cc im nh lin thng.- Quan h K lin thng trong J l mt quan h c tnh cht phn x, i xng,

bc cu, v vy, n l mt quan h tng ng2.4. im binim nh P trong nh nh phn c gi l im bin nu c tn ti t nht

mt im k 4 c mc xm khc vi P. Tp cc im bin ca mt i tng s tothnh bin ca i tng nh .2.5. Chu tuynChu tuyn ca mt i tng nh l tp hp cc im bin: {P1, P2, Pn}

ca i tng nh sao cho hai im Pi v Pi+1 l cc im k 8 ca nhau (i=1..n-1)v P1 l k 8 ca Pn.

K hiu chu tuyn l C=


6

3 2

0

1

4

5

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Hnh v: chu tuyn ca mt i tng nh* Chu tuyn i ngu:Hai chu tuyn C= v CT = c gi l i ngu ca

nhau khi v ch khi mi i (i=1..n) u tn ti duy nht j (j=1..m) sao cho:

- Pi v Qj l cc im k 4 ca nhau- Mc xm ca Pi khc Qj

* Chu tuyn ngoi:Chu tuyn C= c gi l chu tuyn ngoi nn s im bin ca

C nh hn chu tuyn i ngu CT* Chu tuyn trong:Chu tuyn C= c gi l chu tuyn ngoi nn s im bin ca

C ln hn chu tuyn i ngu CT

Hnh v: chu tuyn trong chu tuyn ngoi

3. Mt s k thut d bin trong nh nh phn3.1. D bin hnh thc ha- Nu cc k hiu (b,g) l mt cp im vi b l im nh v g l im nn.- Dy cc cp im (b1,g1), (b2,g2), , (bn,gn) l cc im k 8 ca nhau v

(b1,g1) (bn,gn),- Gi T l thut ton tm bin, p dng thut ton T cho cp im (b i,gi) ta s

tm c cp im tip theo: (bi+1,gi+1) = T(bi,gi)

- Khi p dng thut ton T, qu trnh d bin c thc hin theo th t ttrn xung di v t tri sang phi cho ton b nh.

3.2. Thut ton d bin FreemanXut pht t mt im nh P, qu trnh d bin s i theo cc hng: 0, 2, 4,

6 trong mt n 8 hng. Nu gp im nh th sang tri, im nn th sang phi. Qutrnh trn c lp li cho n khi quay li ng v tr xut pht P. Khi nim sangtri, sang phi ph thuc vo hng n ca im ang xt thay i hng i caim n im tip theo nh trong bng di y.

im nh sang tri im nn sang phiHng n Hng i n Hng n Hng i n


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im tip theo im tip theo

0 2 0 6

2 4 2 0

4 6 4 26 0 6 4

Thut ton Freeman b hn ch kh nng phi xt n nhng im khng cn quantm trong qu trnh d bin. V d di y s th hin iu .nh nh phn c kch thc 8x8 vi im bin xut pht P c ta (2,4)

Nhng im khng cn quan tm: (0,3), (4,7), (7,3), (4,0)

3.3. Thut ton Freeman ci tinXut pht t mt im nh P, qu trnh d bin s i theo cc hng: 0, 2, 4,6 trong mt n 8 hng. Nu gp im nh th sang tri, im nn th quay ngctr li. Qu trnh trn c lp li cho n khi quay li ng v tr xut pht P. Khinim sang tri, quay li ph thuc vo hng n ca im ang xt thay ihng i ca im n im tip theo nh trong bng di y.

im nh sang tri im nn li li

Hng n Hng i nim tip theo

Hng n Hng i nim tip theo

0 2 0 4

2 4 2 6

4 6 4 0

6 0 6 2

Gii thut ci tin s khc phc c hn ch ca gii thut Freeman. V d diy s th hin iu :nh nh phn c kch thc 8x8 vi im bin xut pht P c ta (2,4)


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BI 3CC PHP TON HNH THI TRN NH NH PHN

1. Php ton hnh thi (Morphology)- Hnh thi l thut ng ch cu trc ca mt i tng nh trong c phm

vi v mi quan h gia cc phn ca i tng.- Vi nh nh phn IMxN, im nh ti v tr (x,y) l I(x,y) c xc nh:

= 0 nu l im nn= 1 nu l im nhGi A l tp hp cc im nh, ta k hiu: A={(xi,yi) | I(xi,yi) = 1}Ac l tp hp cc im nn:

V d:

0 0 1 1 0

1 0 0 1 00 1 0 0 0

A = {(0,2), (0,3), (1,0), (1,3), (2,1)}

2. Cc khi nim c bn* Php dch:

Cho mt vector x v tp hp cc im A, php dch A + x c xc nh bi:

* Cc php ton tp hp Minkowski:


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Cho A, B l cc tp hp im:Php cng Minkowski:

Php tr Minkowski:

3. Php gin nh v co nhT hai php ton Minkowski, ta c php ton hnh thi c bn l php gin nh vco nh :

Php gin nh (Dilation)

Php co nh (Erosion)

Trong :

* Mt s tnh cht:

Giao hon:

Khng giao hon :

Kt hp:

Dch chuyn bt bin:

* V d minh ha:

(a) Gin nh D(A,B) (b) Co nh E(A,B)

A v B c th c xem l cc i tng nh v B c gi l phn t cu trc.


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Thng thng, php gin nh lm tng kch thc i tng nh trong khi php conh lm gim kch thc. iu ny ty thuc vo vic chn phn t cu trc. C hai

phn t cu trc ph bin thng c dng l tp hp k-4 v tp hp k-8 trongh ta cc:

(a) N4 (b) N8

ngha:- Php gin nh bin i gi tr ca cc im nn k-4 (hoc k-8) vi im nh thnhcc im nh, do vy, n lm tng kch thc cc im nh.- Php co nh bin i gi tr ca cc im nh k-4 (hoc k-8) vi im nn thnhcc im nn, do vy, n lm gim kch thc cc im nh.V d:

(a) B = N4 (b) B= N8Cc im nh gc l cc im mu xm, cc im thm vo l cc im c mu en.

4. Php m v ng nhChng ta c th kt hp php gin nh v co nh to nn hai ton t quan trnghn:

M nh:

ng nh:* Mt s tnh cht:

- i ngu:

- Dch chuyn:


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ngha:- Php m nh s m rng nhng khong trng gia cc phn tip xc trongi tng nh, lm cho nh bt gai hn.

- Php ng nh s lm mt i nhng khong trng nh trong nh, lm mt inhiu trong nh.

5. Mt s kt quCc ton t cu trc thng c p dng:

(a) (b) (c)

a) nh A b)Gin nh vi 2B c)Co nh vi 2B

d)M nh vi 2B e) ng nh vi 2B f)it-and-Miss viB1 v B2

V d vi cc ton t hnh thi

6. Php ton HitAndMiss

Cho mt nh A v hai phn t cu trc B1 v B2, ta c:


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vi B1 v B2 l gii hn v ri rc nhau (B1 B2 = )

(php ton ny cn c gi l xc nh vin mu, mu B1 cho i tng nhv mu B2 cho nn nh)

* ng vin cc im k 4:

* ng vin cc im k 8:

Mt cch bin din khc:

Biu din phn t cu trc di dng ma trn (gm B1 v B2)

* Cch thc hin: dch chuyn im gc ca phn t cu trc ln lt trn cc imnh theo th t t trn xung di, t tri qua phi, nu cc im nn v im nhca phn t cu trc khp vi trn nh th ta gi li im nh , nu khng ta t

thnh im nn.

4 phn t cu trc c s dng tm gc ca nh trong php ton HitAndMiss(thc cht l mt phn t quay theo 4 hng khc nhau)


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Sau khi tm c gc theo cc phn t cu trc trn, ta kt hp chng li c ktqu l cc gc li ca nh.

S dng php ton HitAndMiss tm gc li ca mt nh7. Xng nh

Khi nim: Xng nh l tp hp cc ng dy l 1, i qua phn gia cai tng nh v bo ton c tnh cht hnh hc ca i tng nh.

Tuy nhin, khng d dng nhn ra xng nh:

V d:

(a) (b)

Trong v d (a), ta khng th tm c ng thng c dy 1 i qua gia itng m phn nh c tnh cht n gin ca i tng. Trong v d (b), ta khngth b i mt im trong i tng k 8 m gi c tnh cht hnh hc ca itng.

Cng thc c bn:

- Cc tp hp con ca xng nh Sk(A):


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vi K l gi tr ln nht ca k trc khi Sk(A) tr thnh rng

(ta c )

Xng nh l hp ca cc tp con xng nh:

Nh vy, i tng nh ban u c th c ti to li t cc tp con xngnh, phn t cu trc B v gi tr K:

Tuy nhin, cng thc ny khng phi lc no cng bo ton c tnh chthnh hc ca nh.

* Php ton lm gy nh:

Cng thc:

Ty thuc vo cch chn B1, B2 m ta c cc thut ton lm gy nh khcnhau.

Mt cch biu din khc:

Phn t cu trc c dng tm xng nh (im gc tm ca phn t cu trc).

Ti mi bc lp, nh s c lm gy bi phn t cu trc bn tri, sau n phnt cu trc bn phi, tip theo vi php quay 90o hai phn t cu trc trn. Qu trnh

c lp i lp li cho n khi php ton lm gy khng dn n s thay i no na.


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Xng nh c tm bng php ton lm gy vi hai phn t cu trc trn

V d v mt s xng nh:


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8. Ti to lp y nh

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