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Nn dliunh

11/01/2013Phm Vit Hng Nhp mn x l nh 1

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Nn dliu l nhmgim thng tin dtha

trong dliugcnhm thu clng thng tin

nhhndliugc

Nhn chung vidliunh cc thut ton nn

nhthngthiuqu 10:1, mts cho ktqu

cao hn (vd: thut ton fratal cho ts nn 30:1)

11/01/2013 Phm Vit Hng Nhp mn x l nh 2

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C th phn loi cc phng php nn dliu

nh theo hai hng

Phn loi theo nguyn l:

Nn chnh xc (nn khng mt thng tin)

Sau khi gii nn ta thu cdliugc

Nn khng bo ton (nn c mt thng tin)

Sau gii nn khng thu c hon ton dliugc

Lidngkhnng c hncamtngiloibdliu


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Phn loi theo cch thcthchin nn: Phng php nn khng gian (Spatial Data Compression)

Thchin nn bng cc munh trong khng gian

Phng php sdngbini (Transform Coding)

Bao gm cc php bininhgc

Phn loi theo trin l cas m ha

Phng php nn thhthnht

Bao gm cc phng php ngin (lymu, gn t m ha) Phng php nn thhth hai

Da vo bo ha catl nn


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Phng php m ha lot di

Phng php m ha Huffman

Phng php LZW Phng php m ha khi

Phng php thch nghi

Bini Cosin v chun nn JPEG


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Phng php Kim t thp

Phng php Kim t thp Laplace (Laplacian pyramid)

Phng php m ha da vo biudinnh

Phng php m ha da vo vng gia tng

Phng php tch-hp


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Pht trin cho nhentrng (en l 1, trng l 0)

Pht hinmtlot bit lpli

V dmtlot cc bit 0 nmgia 2 bit 1 hocngcli

Thay thchuibngchuimigm thng tin

chiu di v ktlp

Chiu di chui c thlnhn 255 nn nu dng

1 byte s c th khng v vy ta c th tchchui di hn 255 thnh 2


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Phng php ny csdng m ha nh

trong nh PCX v BMP

Ta c th m ha sdngchiu di cnhhoc

thch nghi kiu Huffman


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M ha Huffman da vo m hnh thng k Da vo dliugc, tnsutxuthinca cc

k tc tnh ton

Sau gn cho k ttnsut cao m ngn v kttnsut t m di

c pht trin m ha chung cc loidliu

khc nhau tuy nhin chmtsloidliumi

mang lihiuqu mong mun


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Vic m ha ny gip gimlngdliu cho k

txuthinnhiuhn v c thgimlngd

liucnlutr

Tuy nhin trong mtstrnghp m ha theo

cch ny c th gy btlich khng c li (khi

s khc bitvtnsut khng nhiu)

Bao gm hai bc chnh


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Tnh tnsut cc k t trong dliugc Duyttpgctunt

Lpbngtnsut

Spxpbng theo thttnsutgimdn

M ha cc k t

Duytbngtnsut

Ghp 2 k t c tnsutthpnht thnh 1 (tnsutca 2 k

t ny l tngtnsutcatngphn) Thchin cho n khi chcn mtphnt

Kt thc qu trnh ta cmt cy nh phn Huffman


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K t Tnsut

A 24

B 12

C 10

D 8

E 8


K t M ha

A 0

B 100

C 101

D 110

E 111

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c Abraham Lempel, Jacob Ziv pht trintrcri

c Terry Welch nng cp (LempelZivWelch)

Thut ton ny l thut ton nn tin, da vo vic

lpmttin cc k t c tnsut cao

immnhca k thut ny l khnngtchct

inthiuqu cao

C thc dng nn cc loi file nh phn khc

nhau


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LZW da vo mttinlu cc mu c tnsut

cao trong nh

Tingm cc tvng v nghaca n

LZW s lun cpnhttinmi khi c thm

cmt k tmi

Tin c tia 4096 tvngmbohiuqu ( di lnnhtcat m l 12 bit)


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Cu trc tin


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256 tu (0...255) l m ca k t ASCII

T 256 l m cbit (CC Clear Code)

khcphctrnghpsmulp trong nhlnhn

4096 M xa schbo vickt thc m ha vitinc v

btubtinmi

T 257 l m (EOI End Of Information) Gip phn chia file thnh nhiucmnh (file nhng

GIF c nhiunhgpli)


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Cn li l (258...4095) l cc mulpli trong

nh.

512 phntu tin cbiudinbi 9 bit

512 n 1023 biudinbi 10 bit




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w = null;

while ( c k t k ) {

if k l EOI

in ra m ca w;

}elseif wk tnti trong tin {

w = wk;

}else{

thm wk vo tin;

in ra m ca w;

w = k;

}

}

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Kthutgii nn gnnhngclicakthut nn Mtvnlnvi LZW l nusdng m thay i

chiu di th hthng m ha v hthnggii m

phi bit cim m thay ichiu di

Thng thngchiu di m c thay i khi w+k

c thm vo tinvi m 256,512,1024, 2048

(y l cc v tr lm tng di ca m)

V cbit quan trng l v gii nn lun i sau nnmtbc nn victng kch thc m ha ny phi

cthchinchmmtbc trn hthng nn


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c k t k;

in k;

w = k;

while (c k t k )

/*k c th l k thoc m*/{

entry = nghaca k;

in entry;

thm w + entry[0] vo tin;

w = entry;

}

Chuiu tin lun l k t ascii

Nu k l k t, ngha

ca k chnh l kNu k l m th nghaca k chnh l chui m kidin

entry[0] l k tu tincachui entry

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Gis ta mun m ha chui

ABCBCABCABCD

M ASCII ca A l 65, B l 66, C l 67 v D l 68

Tin ban u bao gm 256 k t ASCII v 2

m CC v EOI

Nu m ha bng ASCII dlius l 65-66-67-66-67-65-66-67-65-66-67-68-EOF


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w k u ra M Chui

null A

A B A 258 AB

B C B 259 BC

C B C 260 CB

B C

BC A 259 261 BCA

A B

AB C 258 262 ABC

C A C 263 CA

A B

AB C

ABC D 262 264 ABCD

D EOF D

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u ra s l

65-66-67-259-258-67-262-68-EOF

Kch thcu vo l12x8 = 96 bit

Kch thcu ra 8x9 = 72 bit

Tl nn l 96:72 1.333


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w k u ra M ChuiA A

A B B 258 AB

B C C 259 BC

C 259 BC 260 CBBC 258 AB 261 BCA

AB C C 262 ABC

C 262 ABC 263 CA

ABC D D 264 ABCDEOF

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M ha khi lc u pht trin cho nhentrng

v sau mrng cho nhacp xm bi cc

phng php thch nghi

Bcnhgcsc chia nh thnh cc khi

Nunhgc kch thc M*N

Th nhsc chia ra lm cc khi k*l (vi k v l l rt

nh so vi M v N)

Sau thchin m ha Huffman vi cc khi


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Thutng thch nghi chs thch hpca cc t mtheo mtngha no

Trong trnghpca RLC th nusdngt m cchiu di thay i th ta c phng php RLC thchnghi

Vi m ha khi

Nusdng cc khiging nhau sbclimyu trn nh

khng thunnht C thsdng cc khi c mtchiucnh, chiu kia thay

ida theo ni dung cakhi


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JPEG (Joint Photographic Expert Group) l mtnhdngnhtchunquctc cng nhnnm1990.

JPEG c dng chyu cho nhacp xm v nhmu (vinhentrngktqu khng nnhlm)

JPEG va nn bo ton thng tin va nn khng boton thng tin

Chyu JPEG cbitnvikhnng nn khngbo ton thng tin cho ktqutt trn nhkthutsthng thng


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M ha JPEG gmnhiu cng on

DCT (Discrete cosine transform)


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C th coi qu trnh gii m l qu trnh ngcca m ha.


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Chun nn JPEG thngsdng phn khi 8x8

Vic phn cc khi c kch thcnh v bng nhau

gip vicbini Cosin nhanh hn

Bini Cosin vi cc khi kch thcnh gip tng chnh xc khi tnh ton vi du phytnh (gim sai

s do lm trn)

nhsc chia lm B khi l MB xNB Cc khis c ta (m,n) vi m = [0..MB-1] v n =

[0.. NB-1]


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Trc khi phn khi, nh c thcchuyn

sang YCBCR (hmu ny ginghmu trong

truyn hnh kthuts)

Mtnginhyvi thnh phn Y ( l sng)

hn l thnh phn CB v CR v vynugimtn

sutmuca 2 thnh phn ny th mtngivn

khng nhn ra s khc bit


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Bini Cosin nhmchuynnhtmin khng gian

(spartial domain) sang mintns (frequencydomain)

Trong min khng gian, bcnhthhinln cc mu khidi chuyn trong khng gian

Trong mintns, bcnhthhintc thay icalncc mu khi dchchuyntim ny sang im kia

Vicbini ny nhm gip vic tch v loib

nhngbini khng cnthit cho mtngiddng hn

Mtngithng khng tt trong nhnbit thay i c tnsln (nn ta c th tch v loinhng thay i ny)


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Vimikhi NxN ta s tnh cc hsnh sau:

Vi


N

n

N

n

kk

N

knCos

N

knCosnnx

NkkX

01 02

2211

21

21

212

)12(

2

)12(),(

2),(

1

11

0,1

0,2

1

k

kk

2

22

0,1

0,2

1

k

kk

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Sau khi bini th ta thu licmt ma trn

NxN tngngvi cc hsca cc tns

Cc hs ny quytnhmcng gp ca

cc sng c tnstngng vo bcnh hon

chnh.

Bini Cosin l bini c bo ton nnttc

cc hscsdng ti tonh.


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Vimikhi NxN ta s ti toli cc imnh

sau

Vi


N

k

N

kkk N

kn

CosN

kn

CoskkXNnnx 01 02

2211

212121 2

)12(

2

)12(

),(2

1

),(

1

1

1 0,1

0,2

k

k

k

2

2

2 0,1

0,2

k

k

k

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Huhtnnglngtp trung nhnghs

chnh


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nhgc

Hs 2x2 uHs 4x4 u

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Lngt ha gip cc hscchuynvdngkthutsnhmgimthiulng thng tin

khng cnthit

Thng thng chng ta s quy cc hs trong

cng mtkhivmtkhong phn b

Lngt ha trong nn JPEG l nhmlngt

ha cc gi trhsca php bini


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Kthutca Lloyd-Max chia vng tn hiu thnh nkhong

Vi tn hiu x trong mtkhongsc thay th

bngmt gi tr thay thnh sau

Vi min(x) = L1 < L2 ... Ln < Ln+1 = 1+max(x)

V p1, p2 ... Pn l cc gi tr thay thtngng


1,,)( jjiji LLxpxq

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Muc tiu l tm cc bin Li v gi tr thay th pi saocho li do lngt ha E cgimthiu

y l vncbncashc


m

i

ii xqxE1

2

)(

n

j LLx

ii

jji

pxE1 ,

2

1

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Chng ta mungimthiu E vy nn ttc cco hm tngphnphi l 0


021,

jji LLx

ii

j

pxpE

1

,

,|#1

jji

LLxi

iLLxi

x

p jji

0

jLE

2

1 jj

jppL

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Thng thng cc phng trnh trn khng thgiic m chng ta sdngthut ton sau

lm gnng (chnh l k-trung bnh)

Bc 1: Cpnht pjmi

Bc 2: Cpnht L mi (gi L1 v Ln+1 khng i)


1,| jjiinew LLxxaveragep j

njpp

L

newnew

new jj

j...2,

2

1

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Thng thng trong thct, nh l mt cch nginhn nn JPEG sdng ma trnlngt

ha

Cc hssc chia cho istngng

trn ma trn ny v lm trn nmts nguyn

gnnht. Nhvyvinhnghscatns

cao th khnngc lm trn n 0 l rt cao.

Nhvyschcn cc hscatns cao.


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Thng thng sau khi lngt ha th tintim ha

Vic m ha sctin hnh tiu ha vic

lutrdliu

Spxp theo hnh Zig-Zag trc khi m ha gip

cc hscspxp theo tnsthpn cao


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C 2 cch m ha cc hs M ha hscatngkhimt theo ng Zig-Zag

M ha hs tn sthp trn ttc cc khirititn

stip theo (theo hnh Zig-Zag)

Cch m ha th 2 cho khnng nn cao hn v

n cho php sdng cc bng Huffman khc

nhau cho mitns gip tiu ha khnng mha


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nhgc

x l vi Canny

Nn c bo ton Nn khng bo ton

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C ththy r cc khi 8x8 trn nh nn JPEG


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Phng php Kim t thp Phng php Kim t thp Laplace (Laplacian pyramid)

Phng php m ha da vo biudinnh

Phng php m ha da vo vng gia tng

Phng php tch-hp


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Viphng php kim t thp nhcbini

bngmt php bini (lc low pass)

Sau lynhgctrinhlc low pass

cnhlc high pass nhlc low pass c thu nh thanh 1/4

Vic ny clpilplimtslnnhtnh

Cui cng nhlc low pass nhnht v cc nhlc high pass cao hnscgili


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Phng php kim t thp l mt cch bininhtmin ny sang min kia (gingbini

DCT)

Binimtbcnhgc thnh mtlot cc bc

nh kch thcnhdn (nuxpchng ln nhau

ta s c hnh kim t thp


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Khi cntolibcnhgc, ta chvicthchincc bc theo chiungcli

Vi cch m ha ny khi ti tolinh cc bc

nh high pass s gip gili chi titcabcnh

Trong khi bcnh low pass c trch nhim

cung cp hnh thi chung cabcnh


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Mc d nuchbini, kch thcca kim tthp slnhnnhgc

Tuy nhin do phn cpc thng tin theo cc

cplngt ha v m ha c th gip gimlngdliucnlutrnh

Lutr cc high pass c kch thclnvi sai snhiu

hn (mtngi phn bit km chi titnh) Lutr cc high pass c kch thcnhvi sai s t hn

hn (mtngi phn bit chi titlntthn)


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nhc chia lm nhiu vng c tnh chtngnht Lu l cch xc nhminngnhts xc nh

phctpcathut ton

C thsdngphng php o hm mbocc vng khng b chia qu nh

Sau khi c cc ng bin khp kn th tin hnh m

ha cc ng bin ny bngxpxhnh hc

Tinti m ha nh dng vectorng bin v

texture


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Nhhcvic tch v hpkhcphcimyucacphng php tch v hp

Phng php ny cngsdng m hnh bin-texture

ng bin cn chnh xc (nhycmvimtngi)

Texture (thay itnginh, t nhycmvimtngi)

tng l nh thng thng c slplica cc

mu v mtnh c thc coi l slplicachnh n qua cc hm bini


)(...)()(21

SfSfSfS N

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Ci kh l tm c cc hm f1..fnvi chnh xc vhiuqu cao

Nhn chung tm cc hm ny ta c th

Chia nhnh thnh cc vng Ri kch thc sxs Vimi Ri tm mt vng Di kch thc 2sx2s rtging Ri

Tm mt php bini H(Di)=Ri

Vic tm vng gingmt cch chnh xc l rttnthi

gian, nhngnu vng khng chnh xc th nhkqu

s khng tc chi titcnthit


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V m ha tnrtnhiuthi gian nn phngphp ny khng hiuquvi cc ngdngthi

gian thc

Tuy nhin do gii m rt nhanh v vikhnng

nn rt cao (khong 50:1) cc ngdngnh nn

video chtlng cao lirttimnngvikthut

ny

ch07 - nen anh

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