Nen Anh Dong Dung Wavelet

8/10/2019 Nen Anh Dong Dung Wavelet

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B gio dc v o toTRNG I Hc BCH KHOA H Ni

------------------------------------------------

Lun vn thc s khoa hc

nn nh ng dng wavelet

Ngnh: in t vin thng

Nguyn Hu pht

Ngi hng dn khoa hc: PGS TS. H Anh Tu

H ni 2005


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Mc lc

Trang

Li ni u.................................................................................................. 4Chng 1 TNG QUAN V NN NH Video THEO CHUN MPEG......................................................................................................................... 61.1. Khi nim v Videov phng php nn Video ........................................ 51.1.1. Khi nim Video ..................................................................................... 51.1.1.1. Khng gian mu (Color Space)............................................................ 51.1.1.2. Cc c cu s ho tn hiu Video ........................................................ 61.1.2. Cc phng php nn Video ................................................................... 81.1.2.1. Gim tc dng bit............................................................................ 91.1.2.2. Nn dng tn hiu Video s theo khng gian ..................................... 101.1.2.3. Nn dng tn hiu theo thi gian. ....................................................... 111.1.2.4. Nn hn hp s dng t hp cc phng php trn .......................... 111.1.3. Tham s nn Video. .............................................................................. 111.2. Gii thiu chung v chun MPEG ........................................................... 121.3. Cc khi nim c bn trong nn Videotheo chun MPEG...................... 141.3.1. Cu trc phn cp Video theo chun MPEG. ...................................... 141.3.2. Phn loi frame Video. ......................................................................... 17

1.3.3. Nhm nh (GOP: Group Of Picture).................................................... 191.4. Phng php nn nh Videotheo chun MPEG. ..................................... 211.4.1. M hnh tng qut b m ho Video theo chun MPEG. ..................... 211.4.2. Ly mu thng tin v mu. .................................................................... 221.4.3. Lng t ho. ........................................................................................ 231.4.4. Ni suy nh. .......................................................................................... 231.4.5. D on b chuyn ng. ..................................................................... 241.4.5.1. nh gi chuyn ng (motion estimation). ...................................... 241.4.5.2. B chuyn ng (Motion Compensation). ......................................... 24

1.4.6. Bin i Cosine ri rc. ........................................................................ 261.4.7. M VLC................................................................................................. 271.5. Qu trnh nn Videotheo chun MPEG-1. .............................................. 271.5.1. Tham s c trng. ............................................................................... 271.5.2. Qu trnh m ho.................................................................................281.5.3.Qu trnh gii m..................................................................................32

1.6. Qu trnh nn Videotheo chun MPEG-2. .............................................. 33


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1.6.1. Tham s c trng. ..............................................................................361.6.2. M hnh m ho Non-scalable theo MPEG-2. .................................... 371.6.3. M hnh m ho scalable theo MPEG-2. ............................................38

Chng 2 Mho SCALABLE VIDEO ..............................................42 2.1. Bng lc 1/2 pixel bin i ngc theo thi gian - tnh ton b chuyn

ng................................................................................................................42 2.1.1. Gii thiu ............................................................................................... 442.1.2. Thut ton ............................................................................................. 462.1.2.1 M hnh Video ph bin ...................................................................... 462.1.2.2. Qut lu tin Video vi vct chuyn ng chnh xc 1/2 im nh . 492.1.2.3. Di chuyn cc b m rng................................................................. 512.1.3. Ba tham s m ho bng con s dng IMCTF ..................................... 542.1.4. Kt qu thc nghim ............................................................................. 552.1.5. Tm tt v kt lun................................................................................ 592.2. M ho scalable video .............................................................................. 612.2.1. Khi qut............................................................................................... 622.2.1.1. M ho lai truyn thng..................................................................... 632.2.1.1.1.M ho Scalable SNR ..................................................................... 632.2.1.1.2 Phn gii m Scalable ..................................................................... 662.2.1.2. Embedded Coding and Fine Granularity Scalability ........................ 662.2.1.3. M ho s dng b ng con 3 chiu v m ho Wavelet........................... 692.2.2. H thng tng quan.................................................................................. 702.2.3. Bng con m ho 3 chiu ...................................................................... 712.2.4. T l dng bt m ho............................................................................... 742.2.4.1.H thng dng bt................................................................................ 742.2.4.2. La chn dng bt m ho v truyn dn ......................................... 782.2.5. Kt qu thc nghim ............................................................................. 812.2.5.1. So snh vi m ho Nonscalable ....................................................... 812.2.5.2. So snh m ho LZC v 3D-SPIHT........................................................ 832.2.5.3. M ho tc a phn gii................................................................... 862.2.6. Tm tt v kt lun................................................................................ 91

Ch

ng 3 i t

ng-c s m

ho SCALABLE...............95

3.1. i tng c bn - C s m ho............................................................. 973.1.1 Mt phng i tng Video.................................................................... 973.1.2. Cng c m ho cho i tng Video ................................................... 983.1.2.1. nh dng m ho .............................................................................. 983.1.2.2. Cu trc m ho ................................................................................ 993.2. i tng-C s m ho s dng EZBC................................................ 100


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3.2.1. Tng quan ........................................................................................... 1013.2.2. Min C s bin i Wavelet ri rc .............................................. 1023.2.3. i tng-C s m ho mt phng bt EZBC .................................. 1033.3. Kt qu thc nghim .............................................................................. 104

3.4. Tm tt v kt lun................................................................................. 106Chng 4: Chng trnh th nghim v nh gi ktqu .............................................................................................................. 1114.1. Xy dng chng trnh .......................................................................... 1114.1.1. Khi qu t chung.................................................................................... 1114.1.2. Cu trc chng trnh ............................................................................ 1114.2. nh gi kt qu th nghim ................................................................. 1124.2.1 D liu th nghim.................................................................................. 1124.2.2. Kt qu th nghim................................................................................ 112

4.2.3. Nhn xt v t s nn,cht lng nn....................................................... 115Kt lun..................................................................................................118 1. ng dng lun vn .................................................................................... 1182. Hng pht trin cho tng lai ................................................................. 119TI LIU THAM KHO ............................................................................. 120PH LC...................................................................................................... 122THUT NG ting anh ......................................................................... 122


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Li ni u

Trong nhng nm gn y do s pht trin mnh m ca Internet nn vn

truyn d liu trn mng c bit l truyn nh v m thanh c quan

tm. Do vic nn d liu c bit d liu phim nh l cn thit hn bao giht. Trong phm vi lun vn ny ti tp trung vo vic nn d liu video.

i vi nn nh ng, chun MPEG(Moving Photographic Experts

Group) c xc lp bi ISO v IEC. y l mt k thut nn nh ng

mang li nhiu thnh cng. N c th t t l nn kh cao 10:1 m mt

thng kh phn bit c. Tuy nhin y vn cha phi l t l cao ti u.

S ra i ca Wavelet m ra mt cng ngh mi. l chun

MJPEG2000. S ra i ca MJPEG2000 m ra mt tng lai mi cho k

thut nn nh vi nhng tnh nng cao. K thut Wavelet cng c nghin

cu trong nhiu phn mm nhMatlap...

Mc ch ca lun vn ny nhm nghin cu mt s phng php nn

nh ng ang c quan tm. Lun vn ny c trnh by thnh bn

chng v mt ph lc. Chng Mt ltng quan v nn nh ng. Chng

ny gii thiu mt s chun nn nh ng l MPEG1,MPEG2,MPEG4 v

MPEG7. ng thi cng trnh by cu trc ca video. Chng Hai trnh by

ph

ng php nn Scalable video. Ch

ng ny cp n thut ton LZC v3D-SPIHT. Chng Ba i su vo nghin cu i tng m ho ca video da

trn bin i Wavelet. Chng Bn nu khi qut cch thit k v ci t

chng trnh. Chng ny mang tnh cht minh ho cho nhng g c

trnh by cc chng trc. Phn ph lc nu mt s chng trnh ngun

thng dng vit trn Visual C + + 6. 0.

Do thi gian c hn nn ti ch mi nghin cu c phn no trong k

thut nn nh ng do vy chc chn khng trnh khi thiu st. Cui cng

ti xin chn thnh cm n s gip nhit tnh v hiu qu ca PGS TS HAnh Tu gip ti hon thnh lun vn ny.

H ni ngy 20/10/2005


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Chng 1

TNG QUAN V NN NH Video THEO CHUN MPEG

1.1. Khi nim v Videov phng php nn Video

1.1.1. Khi nim Video

Video l s biu din in t ca mt chui cc nh lin tip. Nhng

nh ny l nhng nh tnh v c gi l cc frame. Chui cc frame xut

hin vi tc rt nhanh s cho ta cm gic chuyn ng lin tc (ti thiu l

25frame/giy). Mc d mi framec s khc nhau, cn thit phi c tc

frame cao t c cm gic chuyn ng thc s. Tc frame v

phn gii ca mi frame l cc nhn t quan trng nh hng trc tip n

cht lng Video. Trong truyn hnh, phn gii ca truyn hnh l 720x576

v tc framel 25 hoc 30 Hz.

1.1.1.1. Khng gian mu (Color Space)

Da theo l thuyt v nh mu, cm th v mu ca mt trn c s 3

mu c bn: mu (Red), mu lc (Green) v mu lam (Blue).

Trong h mu RGB, cc mu c th c m t l cc im bn trong

hnh lp phng n v, vi gc to (0, 0, 0) l mu en; 3 thnh phn R

(), G (lc), B (lam) biu din cho 3 trc.

Mt h thng biu din mu khc c s dng chnh trong lnh vc

truyn hnh nhm gip vic s ha c thun li hn l h mu YUV, miu

t mi nh trong Videogm cc thnh phn chi (Y) v sc mu (UV). H

mu ny nhm t c hiu sut truyn cao hn, v gi nguyn tnh tng

thch vi h s truyn hnh mu en trng. Thnh phn chi ( luminance) cung

cp gi tr mc xm ca nh, hai thnh phn cn li mang thng tin v mu

sc (chrominance) chuyn i t nh xm sang nh mu.


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Chuyn i RGB sang YUV c thc hin theo chun CCIR 601 nh

sau:

Y = 0.299R + 0.587G + 0.114B

U = 0.493 (B - Y)

V = 0.877 (R - Y)

trong : Y l thnh phn chi v U, V l hai thnh phn mu.

c bit: khi R = G = B th Y = R = G = B v U = V = 0.

Mt nh dng mu khc l, tng t YUV l Y, CB, CRvi Y tng t

nhtrn v hai thnh phn nhsau:

CB= U/2 + 0.5CR= V/1.6 + 0.5

Do , mu CB, CRlun nm trong khong [0, 1].

Vi u im trn h YCBCR c p dng rng ri trong vic s ho

Video.

1.1.1.2. Cc c cu s ho tn hiu Video

Hnh 1.1. Cu trc ly mu


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Trong truyn hnh, ccframetrong chui Videoc phn gii l 720

x 576 im v c tc framel 25 hoc 30Hz. Mi nh trong chui Video

c ly s ho nh

hnh 1.1. Cu trc 4: 2: 2

Gi s mt dng ngang ca TV gm 720 im nh.

Hnh 1.2. Cu trc ly mu 4: 2: 2

Vic ly mu s tun t din ra nhsau:

- im u ly mu tn hiu chi (Y) v ly mu 2 mu (CB, CR).

- im tip theo ch ly mu tn hiu chi (Y) v khng ly mu 2 tn

hiu. Khi gii m, mu suy ra t im nh trc.

Tun t nhvy, c 4 ln ly mu Y, c 2 ln ly mu CR, 2 ln ly mu CB.

Cu trc 4: 1: 1


im nh u tin ly mu Y, CR, CB, 3 im k tip ch ly mu Y,

khng ly mu tn hiu mu. Khi gii m, mu ca 3 im nh phi suy ra t

im nh u. Tun t nhvy, c 4 ln ly mu Y, c 1 ln ly mu CR, 1 ln

ly mu CB.

Cu trc ly mu 4: 2: 0


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Ly mu tn hiu Y ti tt c cc im nh ca dng, cn tn hiu mu th

c 4 Y, c 2 mu CRv CBcch nhau theo tng hng.


Cu trc ly mu 4: 4: 4

Ly mu tn hiu Y, CR, CBti tt c cc im nh ca dng.


1.1.2. Cc phng php nn Video

Mc tiu chnh ca vic nn tn hiu Videol biu din mt ngun tn

hiu Videobng mt s bit t nht c th c m vn m bo yu cu cht

lng cm th. Vi tn hiu Video, gii hn di thng ca tn hiu tng t

khong 6MHz, trong khi tn hiu Videos ho theo tiu chun CCIR 601 vi

tc bit l 270Mbit/schim di thng khng di 189MHz, tc l ln hn

31,5 ln so vi di thng ca tn hiu tng t. Chnh v vy, gim di thng l

vn quan trng vi cng ngh Videos.

V c bn gim di thng c thc hin bng 4 cch:

- Gim tc dng bit (bitRate Reduction- BRR).


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- Nn dng tn hiu Videos theo khng gian, tc gim dtha

trong mt sframe(spatial redundancy).

- Nn dng tn hiu theo thi gian, tc gim d

tha theo thigian (temporal redundancy).

- Nn hn hp s dng t hp cc phng php trn.

1.1.2.1. Gim tc dng bit.

C hai phng php gim tc dng bit.

Cch th nht da trn c im sinh l ca mt ngi. Mt ngi

khng nhy cm vi cc tn hiu mu nn trong phng php ny, ngi ta

gim bt phn gii cc tn hiu mu.Cch th hai da trn ngha ca cc bit lng t ho cc im nh.

Vi 8 bit lng t ho, cc bit ca byte ny c chia lm hai nhm: nhm c

ngha hn (MMB-More Meaning Bit) v nhm t ngha hn (LMB-Less

Meaning Bit). Vic ta ct gim cc bit ca nhm LMB s khng nh hng

nhiu ti cht lng ca nh. Tuy nhin, phng php ny khng c chp

nhn trong cc gii php gim di thng hin ti, nn cng s khng c

cp n.Phn ln cc nh dng s thnh phn hin nay u s dng tn s ly

mu 13.5MHzi vi tn hiu chi. Theo chun CCIR 601, nu 2 tn hiu mu

c ly mu c ly mu vi tn s nhtn hiu chi, chng ta s c nh

dng 4: 4: 4.nh dng ny c s dng trong cc thit b dng phim phi

tuyn v trong ho vi tnh lin quan n phim nha. Tc bit ca nh

dng ny cho h PAL l:

Vi lng t ho 8 bit: (720 + 720 +720) x 576 x 8 x 25 = 249Mbit/sVi lng t ha 10 bit: (720 + 720 +720) x 576 x 10 x 25 = 311

Mbit/s.

Trong : 720 x 576 l phn gii mn hnh (576 l s dng /frame).

25 l tc chuyn nh (25frames/s).


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Hin nay, cc thit b s dng k thut s th trng thit b Video

chuyn dng thng s dng chun CCIR 601 4: 2: 2. Theo nh dng s ho

ny, tn hiu Videothnh phn c ly mu vi tn s 13.5MHzi vi tn

hiu chi, v 6,75MHzi vi hai tn hiu mu.

Tc dng d liu ca nh dng ny c tnh nhsau:

Khi ly mu 8 bit: (720 +360 +360) x 576 x 8 x 25 = 166Mbit/s.

10 bit: (720 +360 +360) x 576 x 10 x 25 = 207Mbit/s.

Nhvy, so vi phng php ly mu khng ct gim (4: 4: 4), phng

php ny cho php ct gim c 33% tc dng bit.

Vi nh dng 4: 1: 1 v 4: 2: 0, tc dng bit cn c ct gimnhiu hn. Vi 8 bit ly mu, tc dng bit tnh cho PAL l:

(720 +180 +180) x 576 x 8 x 25 = 124.4Mbit/s.

tc l gim c 50% so vi nguyn mu 4: 4: 4.

1.1.2.2. Nn dng tn hiu Video s theo khng gian

Gn nh tt c cc nh u cha mt s lng ln cc gi tr d liu

thng tin ging nhau. Trong cc h thng khng gim d liu, cc d liu

ging nhau ny c lp li to li cc vng u nhau trong mt nh (v d,bu tri xanh), v do c thng tin dtha trong dng d liu.

gim dtha trong mtframe, ta s dng cc phng php nn

nh. Cc phng php nn nh c th chia lm 2 loi:

Nn khng tn hao (lossless compression): l phng php nn m tn hiu

gc i chiu vi tn hiu c nn (m ho), sau gii nn (gii m) th

khng c s phn bit.

Nn c tn hao (lossy compression): l phng php nn m tn hiu gcc s khc bit vi tn hiu c khi phc sau khi nn v gii nn.

Cht lng hnh nh ca cc thit b dng phng php nn khng tn hao

l rt tt, c th so snh c vi cht lng nh khng nn. Tuy nhin, t

s nn ca phng php ny rt thp. Chnh v vy, cc u im ca vic


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nn tn hiu khng c pht huy mt cch ti a, gi thnh thit b vn

cn rt cao.

nng t s nn, pht huy ti a u im ca vic nn tn hiu,

phng php nn c tn hao c s dng trong hu ht cc thit b hin nay.

C hai nh dng nn c p dng rng ri trong cc thit b truyn hnh, nn

Videol JPEG v MPEG, cng cc phin bn ca n.

1.1.2.3. Nn dng tn hiu theo thi gian.

Cc frame trong Video c quan h mt thit vi nhau, thm ch cc

framehin ti ch thay i cht t so vi ccframetrc v sau . gim

bt thng tin truyn ti, ngi ta ch truyn nhng phn thng tin sai lch v

kt hp vi thng tin c. C nhiu phng php khc nhau xc nh s thay

i gia ccframe, l cc phng php xc nh vct chuyn ng. Ngoi

ra cn nhiu phng php khc, nhng gii thut ny c cht lng cao,

nhng mc tnh ton phc tp v cn ang trong giai on nghin cu.

1.1.2.4. Nn hn hp s dng t hp cc phng php trn

t c hiu qu nn cao m vn m bo cht lng hnh nh,

ngi ta s dng t hp cc phng php trn. Phng php nn Video theo

chun MPEG l mt phng php nn t hp ca cc phng php trn.

1.1.3. Tham s nn Video.

Tham s nn Video c cp n y l nh dng nh v t s

nn, t s nn cho php nh gi hiu qu ca h thng nn. Khi so snh t s

nn ca cc h thng nn khc nhau, th nh dng nh ca cc h thng nn

trn phi ging nhau.

nh dng bao gm:

S dng/nh v s pixel/dng.


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Sframe/s.

V cu trc ly mu bao gm: 4: 4: 4, 4: 2: 2, 4: 2: 0, 4: 1: 1, phn

gii ca mu l 8/10 bit (hoc 12 bit).

Tc bit ca nh gc (trc khi nn) c th rt ra t cng thc:

V d: vi tc bit d liu nh gc 166Mbit/s trn p dng vo my

ghi hnh a PDR-100 (Tektronix), v gi s cht lng nn tng ng

24Mbit/s, th t s nn l 166/24 = 6.92.

1.2. Gii thiu chung v chun MPEG

Chun MPEG (Moving Picture Expert Group) c xy dng v pht

trin bi cc t chc ISO v IEC (InternationalElectrotechnical Commission)

vi mc ch m ho tn hiu hnh nh v m thanh cho DSM (Digital Storage

Media), DSS (Digital Satellite System), HDTV (High Definition Television),

VideoConferencing, Internet Video, v cc ng dng Videos. Chun MPEG

ngy cng

c s dng rng ri trong nhiu ng dng l

u tr, truyn thnga phng tin, v c bit n vi cc chun MPEG-1, MPEG-2, MPEG-4,

MPEG-7.

MPEG-1 (~1992): m ISO/IEC 11172, l chun u tin ca MPEG nhm

mc ch nn Videoc kch thc khun hnh 320x240 cho dng d liu

c tc t 1 n 1.5 Mb/strong cc ng dng DSM (nhcng ngh ghi

VCD), v tuyn truyn hnh.

MPEG-2 (~1995): m ISO/IEC 13818, l chun dnh cho gii php caohn dng trong studio s, DVD, truyn hnh s v HDTV. Khc vi

MPEG-1 tn hiu Video lun l qut lin tc (progressive), MPEG-2 p

dng cho c qut lin tc v qut xen k (interlace). Tc dng d liu

ln ti 15Mb/s.

Tc d liu nh gcT s nn =

Tc d liu nh nn


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MPEG-4 (~1998): m ISO/IEC 14496, l chun ch yu dnh cho cc ng

dng a phng tin tng tc, phn loi khung cnh a phng tin thnh

cc i tng ni dung media, tp trung vo dn knh, ng b d liu vi

cc i tng media truyn qua mng. MPEG-4 s dng tc bit

(Video) rt thp: 564 Kb/s. Vai tr nn t c cp trong phin bn

ny.

MPEG-7 (~2001): MPEG-7 l chun m t thng tin ca rt nhiu loi

phng tin. M t ny cho kh nng tm kim nhanh v hiu qu theo yu

cu ngi dng. Tuy nhin, chun MPEG-7 c m t v phn ni dung

ging nh

MPEG-4, v

c gi chnh thc l Giao thc m t ni dunga phng tin (Multimedia ContentDescriptionInterface). MPEG-7 c

trng cho mt tp tiu chun biu din nhiu loi thng tin multimedia

khc nhau. MPEG-7 khng phi l chun nn.

S gii thiu cc chun nn v cc cng ngh nn xem hnh 1.6:

Hnh 1.6. Cc chun, cc cng ngh nn, truyn thng a phng tin


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1.3. Cc khi nim c bn trong nn Videotheo chun MPEG.

1.3.1. Cu trc phn cp Video theo chun MPEG.

Cu trc dng bit Videoc chia thnh phn cp cc lp (layer) h

tr qun l li, truy cp ngu nhin, dng hnh (editting) v ng b vi dng

bit audio.

Block: L cc khi kch thc 8x8 im nh ca tn hiu chi v mu c

dng bin i DCT.

Macroblock: Mt Macroblockl mt nhm cc khi DCT (theo ni dung

thng tin) trong nh gc. Header ca Marcroblockcha thng tin v cc

khi chi v mu, v thng tin b chuyn ng. C ba loi

Macroblock(phn loi theo phng php m hoMacroblock):

u Skipped MB: s dng d on t framegii m trc vi vct

chuyn ng bng 0. Khng c thng tin v Macroblockc gii

m cng nhc truyn n ni nhn.

u Inter MB: s dng d on b chuyn ng t frame trc . Do

, cn truyn i kiu MB, a ch MB, vect chuyn ng, cc hs DCT v kch thc bc lng t.

u Intra MB: khng dng d on t frame trc . Nn ch cn

truyn kiu MB, a ch MB, cc h s DCT v kch thc bc

lng t n ni nhn.

Slice: Slicecung cp kh nng phng nga s sai lch d liu. Khi gp li

trong dng bit ca mt nh, b gii m c th khi phc bng cch i

Slicetip theo m khng phi hu b ton b nh.Slicecha header v mt

hoc nhiu Macroblock lin tip. Kch thc Slicecc i c th l ton

cnh, kch thc cc tiu c th l mtMacroblock. Header caSlicecha

thng tin v v tr ca n trong nh v h s thang ca b lng t ho.


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Picture(frame): Mt nh tng ng vi mtframeca Video. C ba kiu

nh chnh l: nh I, P v B. Cc nh ny khng c lp nhau, nn th t

dng bit (tc l th t cc cnh c truyn, lu tr v khi phc) khng

theo th t hin th, m l th t cho php b gii m c th gii m dng

bit. Lp nh bao gm phn header v mt hoc nhiu Slice. Header ch th

s sp xp truyn frame, cho php b gii m hin th frameng theo

bc, kiu nh v thng tin m ho.

GOP (Group Of Picture): Mt nhm nh l mt im truy nhp ngu

nhin (random access point), l n v m ho nh nht m c th c

gii m c lp, bao gm phn header v cc nh. Header cha thng tinthi gian v dng hnh (editting). Mt nhm nh GOP hnh thnh t lin

kt mt hoc nhiu frame I, v cc frame P, v/hoc frame B. Cu trc

GOP c biu din thng qua hai tham s: n (s frametrong GOP) v m

(khong cch d on), thng thng n=15, m = 3. Mi GOP bt u bng

mt frameI. Th t cc nh dng m l th t m qua qu trnh gii m

a chng tr li bnh thng. c bit, nh B trong dng gii m c

a ngay ra mn hnh; nh m cui cng ca nhm nh (trong th t trnhdin) l nh I hoc P.

Chui Video (Video sequence): L lp cao nht ca phn cp m ho.

Chui cha mt header, mt hoc nhiu GOP v mt m kt thc chui.

Thng tin quan trng nht cha trong header l kch thc theo chiu

ngang v ng ca mi nh, t l pixel, tc bit ca nh trong chui, tc

nh v cc kch thc ti thiu ca b nh cho b gii m, . . . . khi

gn trng thi ca b gii m. Chui Videov thng tin header to thnhdng bit m ho, c gi l dng s cp VideoES (elementary stream).


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Hnh 1.7. Cc lp video theo chun MPEG

Hnh 1.8. Cu trc dng d liu MPEG


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1.3.2. Phn loi frame Video.

Cn c vo c tnh ca Videoc s dtha khng gian v dtha thi

gian a ra hai phng php nn gim d tha khng gian (m ho

intraframe) v nn gim d tha thi gian tng ng (m ho

intrerframe), v do chia cc frameVideothnh 3 loi l:frameI,frame

P,frameB.

Frame I(Intra CodedPicture):

FrameI lframeu tin trong mi nhm nh ca chui Video,

frameny c m ho tng t nhm ho nh tnh theo chun JPEG.

CcframeI c m ho c lp, khng cn tham chiu n cc frame

khc trong chui Video. M ho cc frameI ch lm gim d tha

khng gian v cho mt t l nn va phi. Frame I c th dng lm

im truy cp ngu nhin trong chui cho b gii m, v c th dng

nhnh l frame tham chiu (reference frame) d on cc frame

khc.

Frame P(Predictive CodePicture):

Qua frame I, b m ho c th d on thun (forward

predection) frame tip theo. Frame c d on gi l frame P

(predicted frame), v frameP cng c th c d on t cc frame

trc . Nhvy, mi frameP c d on t frameI hoc P trc

. Vic m ho nh P c s dng b chuyn ng. Thng tin c

lng chuyn ng ca cc khi nm trong vct chuyn ng. vct

ny xc nh mt Macroblock (MB) no c s dng t nh gc.FrameP cho h s nn cao hn, v c th s dng lm mt frame so

snh, tham chiu cho vic b chuyn ng cho ccframeP v B khc.


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Hnh 1.9. Ni suy b chuyn ng

Frame B(BidirectionallyPredicted 0icture):

B m ho cng c th s dng ng thi d on thun v ngc. Nhng

frame ny gi l frame d on ni suy 2 chiu (Bi-directional

InterpolatedPrediction), hay frameB. Khng nhframeI (c d on

c lp) vframeP (c d on da voframeI hoc P trc ),frame

B c d on 2 chiu da vo cp frameI v P, hoc P v P, hoc P v I

(vi frame I ca nhm nh tip theo). Vic s dng thng tin ly t nh

trong tng lai hon ton c th thc hin c v ti thi im m ho th

b m ho sn sng truy cp ti nh pha sau.FrameB cho t l nn caonht, v khng c dng lmframetham chiu.

Theo phng php nn ny,frameI gi lframeintra(s dng k thut

m ho intraframe),frameP v B gi l ccframeInter(s dng k thut m

ho interframe).


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Mt thun li khi s dng nhiu loiframel theo di d liu trong

qu trnh truyn, nu c frameb mt (thng l frameP hoc frameB) th

cht l

ng Videocng khng b nh h

ng nhiu.Kch thc ccframec minh ho trong hnh v sau:

Hnh 1.10. Kch thc cc loi frame

1.3.3. Nhm nh (GOP: Group Of Picture).

Cng ngh MPEG s dng 3 loi nh I, P v B, trong P, B khngphi l mt nh hon chnh m ch cha s khc bit gia nh v nh xut

hin trc (i vi P), hay s khc bit i vi c nh xut hin trc v

sau n (i vi B). c mt khun hnh hon chnh nh P v B cn c d

liu t cc nh ln cn, chnh v vy i vi MPEG c mt khi nim l GOP

(nhm nh). Mi nhm phi bt u bng mt nh hon chnh I v tip theo l

mt lot cc nh B, P. C hai loi nhm l m v ng. Nhm m bt u

bng mt nh I v kt thc bng mt nh I, vic d on nh ph thuc c vothng tin ca cc GOP khc. Nhm ng c cu trc khp kn, vic d on

nh khng ph thuc vo thng tin ca nhm khc v nh cui cng ca mt

nhm bao gi cng l mt nh P.


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Chui nh MPEG thng c cu trc IBBPBBPBBI nhng th t truyn

dn v th t hin th nh l khc nhau do khi to nh B cn thng tin t c

khung qu kh v tng lai. nh tng lai cn phi c truyn dn trc, khi

hin th phi theo ng th t ngun. thc hin iu ny, lp nh (Picture

layer) ca dng d liu MPEG c thng tin v s th t nh tr gip hin

th. Hnh di trnh by th t truyn dn v th t hin th nh.

Hnh 1.11.Th t truyn dn v th t hin th nh

Chun MPEG khng nh ngha s lng gii hn ccframeB lin tip

trong nhm nh, nn s lngframeB lin tip ph thuc vo tng ng dng.

Thng thng, s lng ny l 2 (I, B, B, P, B, B, P) m bo hiu qu nn

v cht lng Video.

Mt cu trc nhm nh thng thng c m t bi hai tham s: n - snh trong mt nhm v m - s khong cch cho nh B. Nhv dtrn n=9 v

m=3.


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1.4. Phng php nn nh Videotheo chun MPEG.

1.4.1. M hnh tng qut b m ho Video theo chun MPEG.

Nn Video s nhm mc ch loi b d tha khng gian v d tha

thi gian trong chui Videom khng nh hng n mc cm th ca mt

ngi.

Trong phng php nn Video theo chun MPEG c hai k thut nn

c s dng l:

K thut m ho Intraframe: K thut m ho Intraframe nhm gim

d tha khng gian trong mt frame. K thut ny xut pht t mi

tng quan khng gian gia cc im nh trong mt nh, t nn nh

hiu qu. Phng php c s dng gim d tha khng gian l k

thut m ho bin i Cosine ri rc (DCT) trn cc khi 8x8 im nh.

K thut ny c s dng trong phng php nn nh tnh trnh by

Chng 2.

K thut m ho Inter frame: nhm gim dtha thi gian gia cc

framenh: K thut m ho Inter frame tnh gi tr ca mt im nhring bit bng cch d on t cc im nh trong nh ln cn. K thut

ny xut pht t mi tng quan thi gian gia cc im nh trong cc nh

ln cn. Phng php gim d tha thi gian l k thut m ho

DPCM da trn d on b chuyn ng gia ccframe.

Trong m hnh nn Videotheo chun MPEG, t c hiu qu nn cao

cn kt hp c hai k thut nn trn gim dtha khng gian v thi

gian. M hnh nn Video Hybrid DPCM/DCT l s kt hp ca hai kthut trn (xem hnh 1.12).

M hnh Hybrid DPCM/DCT gm c cc k thut:

Ly mu (subsampling) thng tin v mu thch hp vi nhy cm ca

mt ngi.


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Lng t ho (Quantization-Q)

Ni suy nh (picture interpolation).

D on b chuyn ng bao gm: nh gi chuyn ng (motionestimation) v b chuyn ng (motion compensation-MC)

Bin i Cosine ri rc (DCT) khai thc tnh dtha khng gian.

M ho chiu di thy i (VLC-Variable length coding).

Hnh 1.12. Nguyn l m ho Hybrid DCT/DPCM

1.4.2. Ly mu thng tin v mu.

Ly mu vi tn s ly mu thp hn l gim kch thc ca Video

u vo v nhth s gim s lng cc im trc khi m ho.Ly mu mu ngha l ly mu mu tn s thp hn tn s ly mu

theo l thuyt Nyquist hoc Shannon.

Mt ngi nhy cm nht vi phn gii thnh phn chi ca nh

v t nhy cm vi thng tin v mu. Ly mu l mt phng php gim d


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liu rt c hiu qu, nhng s tn tht phn gii nh v cc thnh phn

chng ph s lm gim cht lng ni dung nh gc. V l do ny, nn khng

dng ly mu thp cho tn hiu chi. Cu trc ly mu thng dng l 4: 2: 2

v 4: 2: 0. MPEG dng cu trc 4: 2: 0.

1.4.3. Lng t ho.

Lng t ho c thc hin bng cch chia mi h s DCT cho cc gi tr

kch thc bc lng t tng ng trong bng lng t, sau lm trn v s

nguyn gn nht.

( , )( , ) ( , )

q

S u vS u v Q u v

=

trong :

- [] l lm trn v s nguyn gn nht.

- Q(u,v): h s lng t ho xc nh bi bng lng t ho. Q(u,v) c

gi tr t 1 n 255 xc nh bc ca kch thc lng t ho tng

ng.

Gii l

ng t ho

c thc hin bi:'( , ) ( , )* ( , )qS u v S u v Q u v=

1.4.4. Ni suy nh.

B gii m c th khi phc nh hin ti t nh trc v nh sau, th k

thut khi phc gi l k thut ni suy nh. Cc khi trong nh hin ti c

th c d on thun hoc ngc v c dch theo cc vct chuyn ng.

B gii m c th ti to cc gi tr im nh theo mt khi cho tr

c l trungbnh ca cc gi tr ca khi trc v khi sau.


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1.4.5. D on b chuyn ng.

1.4.5.1. nh gi chuyn ng (motion estimation).

nh gi chuyn ng l qu trnh nh gi xp x cc im caframe

hin ti tframetham chiu.

nh gi chuyn ng phi xc nh cc vct chuyn ng, v c

thc hin ti b m ho vi nhiu s tnh ton phc tp. C nhiu chin lc

tm kim xc nh vct chuyn ng. Vi mi chin lc tm kim, b m

ho c gng i snh cc im trong mt Macroblockvi cc im trong nh

c m ho trc hoc sau (theo th t hin th). Khi qu trnh tm kimkt thc, s to ra vct chuyn ng (motion vct) thch hp nht (xem hnh

1.13).

Hnh 1.13.Xc nh vect chuyn ng mv(motion vector)

1.4.5.2. B chuyn ng (Motion Compensation).

Trong thc t th khng phi khi tng thch lc no cng gi nguyn

trng thi cn bng sau khi dch chuyn m trong qu trnh dch chuyn n b


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quay i mt gc no . Vi gc quay nhvy s lm cho nh sau khi xy

dng li s b lch i mt gc no (lch hnh). khc phc tnh trng

ngi ta a vo khi nim nh li d on. nh sai s d on l phn khc

nhau nh nht gia nh hin ti c truyn v nh d on tt nht c th t

c. nh c xc nh bng cch ly nh hin ti tr i i nh sau khi d

on. Qu trnh xy dng li nh c thc hin bng cch ly nh d on

thng qua vct chuyn ng cng vi sai s d on. Khi m ho thay v

phi m ho ton b nh ngi ta ch cn m ho vct chuyn ng v nh

sai s d on. nh sai s d on c kch c nh hn rt nhiu so vi ton b

nh v phn nh ging nhau s b trit tiu (c gi tr bng 0) khi xc nh nh

sai s d on, do vic m ho s i hi t byte hn.

Qu trnh khi phc mt nh bng cch dng cc phn nh t nh trc

cng vi thng tin v chuyn ng (vct chuyn ng) nh trn gi l b

chuyn ng(Motion Compensation).

Trong nhm nh trn (hnh 1.11), nh I1c gii m m khng cn xt

n vct chuyn ng, nhng nh P4c gii m phi s dng vct chuyn

ng t nh I1. B chuyn ng ny gi l b chuyn ng thun v xui theotrnh t thi gian. Cc nh P lun dng b chuyn ng thun t nh I hoc P

c truyn trc . Cc nh B c gii m s dng b chuyn ng t nh

I hoc nh P trc hoc sau (theo th t hin th).

D on c gi l thun nu nh tham chiu (nh I hoc nh P) l

nh trc nh ang xt; v c gi l ngc nu nh tham chiu l nh sau

ang xt (theo th t hin th).

V dtrong hnh 1.11 nh B2dng b chuyn ng thun t nh I1v bchuyn ng ngc t nh P4. .Do , nh B2dng b chuyn ng hai chiu

v kt qu ly trung bnh, nn c gi l b chuyn ng ni suy.

B chuyn ng c thc hin ti b m ho v gii m.


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Qu trnh khi phc frame (vi loi frame inter) s dng b chuyn

ng gm hai bc:

+ Cng vct chuyn ng voframetham chiu.

+ Cng sai s d on v kt qu trn.

Hnh 1.14 minh ho qu trnh khi phcframe.

Gia nhng im k tip nhau c lin quan ln nhau dn n s d

tha. M d on c dng loi b s dtha . Da trn qu trnh to

cc im tun t v lut d on, mi gi tr ca im c th c d on

thay th im hin ti. Phn chnh lch gia im d on v im hin ti

c m ho. Thnh cng trong m ho t bit hn so vi m ho trc tip imhin ti.

M ho d on ng vai tr quan trng trong cc chun nn nh nh

JPEG v MPEG c hiu sut nn v n gin hn.

Hnh 1.14.Minh ho qu trnh khi phcframe

1.4.6. Bin i Cosine ri rc.

Tng t nhbin i DCT.


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1.4.7. M VLC.

M ho VLC l phng php m ho thng k, gn cc t m cho cc

gi tr c m ho. Cc gi tr c tn s xut xut hin cao c gn t m

ngn, cc t m c tn xut xut hin thp c gn t m di hn sao cho

xu biu din m ngn hn so vi d liu gc. Vi cch gn trn, m ho c

gi l m ho c di thay i nhm ti u vic m ho vi s lng bit t

nht.

1.5. Qu trnh nn Videotheo chun MPEG-1.

K thut nn Video theo chun MPEG -1 ch yu ng dng cho vic

lu tr trn CD-ROM v truyn trn mng. u vo Video theo chun bao

gm mt nh dng nh Videolin tc (non-interlaced)

1.5.1. Tham s c trng.

Tham s c trng cp n y l nh dng nh u vo v cu

trc ly mu. nh dng u vo l: 720 im mi dng, 576 dng mi nh v

30 nh mi giy.

T l bit ln nht l 1.86Mbit/s.

Cu trc ly mu l 4: 2: 0.


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1.5.2. Qu trnh mho.

Hnh 1.15.S khi b m ho video theo chun MPEG-1

Quy trnh hot ng ca b nh gi xp x chuyn ng v b chuyn

ng theo chun MPEG-1 gm:

1.5.2.1. B nh gi chuyn ng.

Thao tc cho tng khi ti mi thi im.

Vi mi khi caframehin ti:

Tm kim khi ging nht trongframetrc.

Tnh ton vect chuyn ng t khi ging nht .

Xc nh sai lch gia khi thuc framehin ti v khi thuc frame

trc .

M ha vct chuyn ng.

M ho khi sai lch.

Php tm kim thc hin trn mt vng gii hn, gi l vng tm kim.


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1.5.2.2. B b chuyn ng.

B m ho dng vct chuyn ng v frame tham chiu to ra

framed on b chuyn ng caframehin ti.

Mi khi caframehin ti (tc miMacroblock16x16 im) c d

on da vo thng tin v chuyn ng (tc vect chuyn ng) v

frametham chiu.

Khi hin ti tr i khi d on to ra khi sai lch b chuyn

ng.

Khi sai lch ny c bin i DCT, lng t ho v m ho.

Sau khi m ho, khi sai lch ny cng vi vct chuyn ng c

truyn i.

1.5.2.3. Qu trnh m ho.

Mt bn sao khi phc tframe m ho c lu tr trong vng m

frame(frame store), frameny c dng nhframetham chiu cho

nh gi chuyn ng. Th t lu tr trong FS ca b m ho phi ng

nht vi th t ny trong b gii m.

B nh gi chuyn ng tnh ton vct chuyn ng cho mi khi

bng cch i snh frameu vo hin ti vi frame tham chiu gn

nht.

B b chuyn ng to ra frame d on b chuyn ng (l frame

gingframehin ti nht).

Framehin ti tr iframeb chuyn ng to raframesai lch b

chuyn ng.

Cc h s sau khi lng t ho v cc vct chuyn ng c m ho

v truyn i.


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ng thi, cc h s lng t ho c lng t ho ngc, bin i

ngc, v cng viframed on b chuyn ng to raframetham

chiu mi.

Cch hot ng ca b m ho ph thuc vo tng loiframe.

FrameI c x l theo cch thc tng t nhphng php nn nh

tnh theo chun JPEG.FrameI c lu tr trong b mframe lm

frametham chiu dng cho nh gi chuyn ng v to ra ccframeP

v B.

FrameP khng c m ho trc tip nhframe I, m m ho frame

sai lch giaframeP hin ti vframed on (thun) ca n. Framed on c to ra nh s dng vct chuyn ng vframeI, hoc P

c tham chiu gn nht.

Tng t nhframeP,frameB khng c m ho trc tip m m ho

framesai lch gia frameB hin ti v framed on (hai chiu) ca

n. Frame d on c to ra nh s dng vct chuyn ng hai

chiu v cpframeI v P, hoc P v P, hoc P v I c tham chiu gn

nht.

Qu trnh m hoframeI:


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Hnh 1.16. Qu trnh m ho frame I

Qu trnh m hoframesai lch:

Hnh 1.17. Qu trnh b chuyn ng v m ho frame sai lch

Tc bit ca tn hiu Videoc nn khng c nh, ph thuc vo

ni dung nh ang xt. Ngc li, ti u ra b m ho, dng bit phi c nh


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xc nh tc cho dung lng knh truyn. Do , trc khi truyn i, ti

u ra b m ho phi c b nh m ln. B m ho phi kim tra trng

thi y (overflow) ca b nh m. Khi s liu trong b nh m gn bng

dung lng cc i, th cc h s bin i DCT c lng t ho t chnh xc

hn. Trong trng hp ngc li, c ngha l b m cha s liu qu t

(underflow), th chnh xc ca vic lng t ho cc h s s tng ln. B

nh m c thit k theo kiu FIFO (First In First Out) v c kch thc

khai bo trong dng d liu ra gii m.

1.5.3.Qu trnh gii m.

S gii m:

Hnh 1.18.S khi b gii m video MPEG-1

Gii m l php bin i ngc ca m ho, nhng n gin hn do

khng cn thc hin nh gi chuyn ng, v cng t la chn hn.

B gii m thc hin nhsau:

- Gii m cc vct chuyn ng v cc h s.- Cc h s c lng t ho ngc v bin i ngc to ra frame

sai lch.

- Framec khi phc trc (lu tr trong vng mframe) kt hp

vi cc vct chuyn ng to raframeb chuyn ng.


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- Khi phcframehin ti bng cch cng framesai lch vi frameb

chuyn ng.

- Frame hin ti li c lu tr trong vng m frame xy dng

frametham chiu mi.

Trc khi cc cnh c trnh din, chng cn phi c sp xp li

theo th t trnh din t nhin ca n. Sau khi sp xp, cc nh c trnh din

theo phng php m mi ng dng la chn.

Hnh 1.19.Sp xp th t hin th

Ch : B m ho v b gii m phi s dng th tframetham chiu

ging nhau trong vng mframe trnh trng hp b lch hnh (drift), do

ccframetham chiu b sai trt t trong b chuyn ng.

Hnh 1.18 v 1.15 l s khi n gin (khng xt trng hp m ho

v gii m frameB). Trong trng hp i vi frameB, cn c 2 vng m

framev 2 mch xc nh vct chuyn ng v b chuyn ng.

1.6. Qu trnh nn Videotheo chun MPEG-2.

K thut nn Videotheo chun MPEG-2 l siu tp hp (superset) cc

k thut ca chun MPEG-1 v n c thit k trn c s k tha MPEG-

1.Rt nhiu gii thut m ho Video c tch hp v mt c php n

nhm tho mn yu cu ca cc ng dng.


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im c trng mi ca phng php nn Videotheo chun MPEG-2 l

m ho c Videoxen k (interlaced Video). Hn na nhng m rng ca

m ho Videoscalable

c thc hin cung cp thm cc chc nng nh

l m ho nhng ca TV v HDTV s, v s gim cht lng t (graceful

degradation) khi xut hin cc li truyn dn.

Tuy nhin trn thc t khng th thc hin c c php y cho

hu ht cc ng dng. MPEG-2 a ra hai khi nim Profiles v Level qui

nh s ph hp gia thit b khng h tr kh nng thc hin y . Cc

ProfilevLevelcung cp mt phng tin cho vic nh ngha cc tp con c

php v nhvy b gii m c kh nng gii m mt lung bit c bit. Khinim ny c minh ho bng bng 1.1 v 1.2.

Theo nguyn tc chung, mi Profilenh ngha mt tp mi cc gii

thut c thm nh l mt siu tp hp vo cc gii thut trong Profile

di. Mt Levelxc nh di cc tham s c cung cp khi thc hin nh

kch thc nh, tc framev tc bit. Nng ct ht nhn ca MPEG-2 ti

MAIN Profilem t nhng nt ni bt m ho Non-scalable ca c ngun

nh Video lin tc (progressive) v xen k (interlaced). Ngi ta mong i

rng hu ht cc thc hin MPEG-2 s ph hp vi MAIN Profileti MAIN

Level. MAINProfilecung cp kh nng m ho Non-scalablecho nh Video

s vi cc tham s gn ging TV l mt ly mu cc i l 720 mu vi

mi dng v 576 dng cho mi frame, tc framecc i l 30 framemi

giy v tc bit ti a l 15Mbit/s.


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Profile Thut ton

HIGH

H tr tt c cc tnh nng c cung cp bi Spatial

ScalableProfilecng vi s cung cp cc h tr sau:

3 lp vi cc ch m ho SNR v Spatial

scalable.

Biu din YUV vi cu trc 4: 2: 2 cho ci thin

cc yu cu cht lng.

SPATIALScalable

H tr tt c cc tnh nng cung cp bi SNRScalable

Profilecng vi mt thut ton cho: M ho SpatialProfile(cho php 2 lp).

Biu din YUV vi cu trc 4: 0: 0.

H tr tt c cc tnh nng cung cp biMAINProfile

cng vi mt thut ton cho:

M ho SNRScalable(cho php 2 lp).


MAIN

Thut ton m ho Non-scalableh tr cc tnh nng cho:

M ho nh Videoxen k.

Truy cp ngu nhin.

Cc ch d on nh B.


SIMPLE

Bao gm tt c cc tnh nng cung cp bi MAINProfile

nhng: Khng cung cp cc ch d on nh B.


Bng 1.1. Cc thut ton v cc tnh nng h tr vi mi Profile


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Level Cc tham s

HIGH

1920 mu/dng.

1152 dng/frame.

60frames/giy.

80Mbit/s/

HIGH 1440

1440 mu/dng

1152 dng/frame. 60frames/giy.

60Mbit/s.

MAIN

720 mu/dng

576 dng/frame.

30frames/giy.

15Mbit/s.

LOW

352 mu/dng

288 dng/frame.

30frames/giy.

4Mbit/s.

Bng 1.2. Cc gii hn trn ca cc tham s ti mi Level ca mt Profile.

1.6.1. Tham s c trng.

Tham s c trng cp n y l nh dng nh u vo v cu

trc ly mu. nh dng u vo l: 720 im nh cho mi dng, 576 dng


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cho miframev 30frame(nh) mi giy choMainProfilevMainLevel. T

l bit ln nht l 15Mbit/s. Cu trc ly mu l 4: 2: 2.

1.6.2. M hnh mho Non-scalable theo MPEG-2.

i vi MAIN Profile: Nguyn tc m ho y l s m rng trc

tip ca nguyn l m ho trong MPEG-1 iu chnh m ho Videoxen k,

trong khi vn duy tr phm vi y ca cc chc nng cung cp bi MPEG-

1.

Cng ging nhchun MPEG-1, thut ton m ho MPEG-2 da trn nguyn

l m ho Hybrid DCT/DPCM nhhnh 1.12.

i vi SIMPLEProfile: Nguyn l m ho cng tng t nhMAIN

Profile, nhng n khng s dng cc m hnh d on cho frameB b m

ho. Nhvy, phc tp khi thc hin v khi lu tr ccframetham chiu

cho vic gii m nh B khng cn cho b gii m ca chun MPEG-2 (ch i

vi SIMPLEProfile).

tho mn cho vic m ho c Videolin tc v xen k, MPEG-2 a

vo khi nimframe picturevfield picturet

ng ng vi hai ch d onlframe predictionvfield prediction iu tit m ho nh Videolin tc

v xen k. i vi chui xen k (interlaced sequence), mt frame gm hai

trng: mt trng chn (even field-bottom field) v mt trng l (odd field-

top field). C hai trng ny c th c m ho c lp. Khi mt trng

c chia thnh cc Macroblock v p dng m ho nh mt frame trong

MPEG-1. Hai trng cng c th c m ho ng thi, khi vic m ho

tr thnh m ho truyn thng ca chui Videolin tip.


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Hnh 1.20. Khi nim frame picture, field picture v d on trng

(field prediction).

Cc nguyn l d on trng b chuyn ng (motion compensated

field prediction) d on chuyn ng ca field picture tng ng (xem

hnh 1.20). Trong field prediction, d on c to ra mt cch c lp cho

mi trng da trn mt hoc nhiu trng tham chiu. Trong trng top

c d on t trng toptrc hoc t mt trng bottomtrc thuc

cng mt nh. Trong mt field picture tt c cc d on l d on trng

(field prediction). D onframec th s dng nhtrong MPEG-1 hoc c

th s dng nhhai d onfieldkt hp. Nhvy trongframe picturec th

s dng d onframehoc field.

1.6.3. M hnh mho scalable theo MPEG-2.

Mc ch ca m ho scalablel cung cp s thao tc gia cc dch v

khc nhau v h tr cc dch v mt cch linh hot vi cc kh nng biu din

khc nhau.

Cc b thu nhn hoc khng c kh nng hoc sn sng xy dng li

Videovi phn gii y c th gii m cc tp con ca dng bit phn

lp biu din Videotrong phn gii khng gian hoc thi gian thp hn

hoc vi cht lng thp hn.


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Mt ng dng quan trng cho m ho scalablegm c vic lit k c s

d liu Videov biu din li a phn gii ca Videotrong cc mi trng a

ph

ng tin. Chun MPEG-2 chun ho 3 nguyn l m ho scalablel: SNRscalability,Spatial scalabilityv temporal scalability. Mi nguyn l c mt

chc nng ring nhm h tr cho cc ng dng c yu cu ring bit. C th

kt hp cc cng c scalabilitykhc nhau thnh mt s m ho hybrid, c

ngha l s tng tc gia cc dch v k c phn gii khng gian v t l

framekhc nhau c th c h tr bng cch kt hp Spatial scalabilityv

Temporal scalability. Ngoi ra s tng tc gia cc dch v HDTV v SDTV

c th c cung cp km theo kh nng hiu chnh cc li knh truyn bngcch kt hp s m rngSpatial scalabilityvi cng c SNR scalability.

Spatial scalability:

u c pht trin h tr hin th cc phn gii khc nhau ti b thu

nhn. Ngha l nh Videoc phn gii khng gian thp c th c khi

phc t lp c s. Tnh nng ny rt hu hiu cho rt nhiu ng dng bao

gm m ho nhng cho cc h thng HDTV/TV, cho php chuyn cc dch

v TV s n cc dch v HDTV vi phn gii khng gian cao hn.

u Thut ton da trn phng php tip cn hnh chp truyn thng cho m

ho nh lin tc.

u C kh nng h tr mt cch linh hot cho mt phm vi rng phn gii

nhng khi phc tp tnh ton trong MAINProfilecng s tng.

SNR scalability:

u Cng c ny c pht trin cung cp s suy gim cht lng uyn

chuyn (graceful degradation) ca cht lng Video trong mi trng

truyn u tin.


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u Thut ton thng s dng c c s suy gim uyn chuyn (graceful

degradation) da trn k thut scalabilitytun t (DCT-domain).

u

Ti lp c s, cc h s DCT c lng t ho v truyn th t ccht lng va phi v gim t s bit (xem hnh 1.21).

u Lp nng cao m ho v truyn s khc nhau gia cc h s DCT khng

c lng t v h s DCT c lng t t lp c s vi kch c bc

lng t tt (xem hnh 1.21).

u Ti b gii m, tn hiu Videocht lng cao nht c xy dng li bng

cch gii m dng bit c lp c s v lp nng cao (xem hnh 1.22).

Temporal scalability:

u Cng c c pht trin vi mc ch tng t nhSpatial scalability.

Phn vng d liu:

u Cng c ny nhm tr gip hu b li c mt trong khi truyn t hoc li

knh truyn trong ATM, truyn thng hoc cc mi trng thu m hp

dn.

u Thut ton l tng t nhcng c SNR scalability, da trn s phn chia

cc h s v c thc hin vi phc tp thp so vi cc s scalable

m ho khc.

u Cung cp s bo v li, cc h s DCT m ho trong dng bit c chia v

truyn mt cch n gin trong hai lp vi kh nng xy ra li khc nhau.


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Hnh 1.21.B m ho hai lp cho m ho SNR scalable ca video

Hnh 1.22.B gii m cho m ho SNR scalable ca video


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Chng 2 M ho SCALABLE VIDEO

2.1. Bng lc 1/2 pixel bin i ngc theo thi gian - tnh ton b chuyn

ng

t hiu qu cao trong nn tn hiu Videongi ta phi tm cch loi

b dtha v mt thi gian bi do cc khung st nhau c s tng quan rt

ln. Trong cc h thng m ho Video (v dMPEG-1, 2 [7, 8] v H.261/263)

s d tha v mt thi gian c loi b nh k thut m ho lai (hybrid

coding technique), b chuyn ng iu xung m vi phn (DPCM) v bin i

m ho. Trong k thut ny cu trc xung trc c s dng d on

xung hin thi sau khi b chuyn ng nhhnh 2.1. Kt qu l khung sai

khc thay th c nng lng thp hn tn hiu ngun s c truyn i v

c m ho. Theo cch ny s dtha ca cc khung lin tip nhau s c

s dng tt.

Tuy vy vn c mt s vn xy ra, l: Th nht, khi gim s d

tha thi gian th tc bit m ho cng gim. Kt qu l hiu qu nn gim

khi tc bit thp. Th 2, vic m ho dng DPCM ch c thc hin khi c

xung tip theo. Th 3, vic xc nh v tr bit ti u phc tp ph thuc vo

khung c lng t ho.

Bin i m ho 3 chiu (3-D) l mt phng php tip cn c hiu qu

trong nn Video. Hnh 2.2 cung cp s khi tng qut ca h thng m ho

Video3 chiu. Trong hnh 2.1, ta thy b bin i 3 chiu khng cha mch

vng DPCM trong b m ho lai. Do n th trnh c nhng nhc im

ca phng php m ho truyn thng. Tuy nhin vic bin i trc tip

thng gp kh khn vi b nh cao v m ho c tr.


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Chng ny xin gii thiu mt h thng m ho Video3 chiu mi, kt

hp gia bng lc MC-3D v thut ton m ho mt phng bit EZBC s c

trnh by trong chng tip theo. Phn sau chng ta s nghin cu cc cng

vic lin quan n vic hnh thnh m ho bng con 3-D. Mc 2.1.2 miu t

ton b lc phn tch tng hp bng con. Mc 2.1.3 miu t h thng

bng con 3-D vi cu trc MC3D-FSSQ. Mc 2.1.4 trnh by nhng kt qu

thc nghim.

Hnh 2.1. S b m ho

Hnh 2.2. S b gii m


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2.1.1. Gii thiu

M ho wavelet bng con 3-D cho Video c tng cng nghin

cu trong nhng nm gn y bi nhng u im quan trng ca n so vi

phng php bin i truyn thng DCT.

Karlsson v Vetterli l ngi u tin khi qut vic pht trin t m

hnh hai chiu ln ba chiu. Mt cp bng lc Haar 2 chiu, kt hp vi khung

thng thng v sai khc, c chn cho bng lc thi gian trnh tr m

ho v b nh ln. Do s thc hin khng qu phc tp lc ny vn c

s dng rng ri trong h thng m ho bng lc 3 chiu. Tuy nhin khi tn

hiu Videou vo yu cu tc nhanh khng th dng c phng php

ny.

Ba tham s cho m ho wavelet/bng con b chuyn ng cc b s

c trnh by phn sau. Thay v thc hin trc tip nh u vo, thut ton

bng lc theo thi gian s c tin hnh theo ng chuyn ng ca nh.

Nh s gim c s d tha nng lng ca bng lc thng cao. Trong

phng php Kronander da trn 3-DDCT v m ho bng con 3-D, tn hiu

dtha thm vo c m ho vi pixel ch khng theo vect chuyn ng.

Trong phng php TRI-ZTR cho tc Videothp, cc im nh c sp

xp theo vt chuyn ng cho bng lc thi gian b chuyn ng. Tuy nhin,

nh hng ca a kt ni v khng kt ni trong b m ho b chuyn ng

c b qua trong phn ny. Kt qu h thng phn tch v tng hp khng

th khi phc hon ho khng thch hp cho ng dng m ho Video tc

cao. Hnh 2.3 minh ho thut ton m ho ca b lc b chuyn ng theo

thi gian. Tnh chnh xc ca bng lc s t c khi b b chuyn ng

thc hin vi im nh y .

iu ni ln rng b chuyn ng vi mt na im nh l cn thit

tng hiu qu trong vic lm gim nng lng ca khung sai khc. Do u


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ra ca bng lc thng cao, Haar ch kt dnh gia khung hin ti v trc ,

bng lc thi gian b chuyn ng vi mt na im nh c la chn

lm gim tn s nng lng bng con.

Php ni suy c s dng cho im nh trong li con c trng

hp phn tch v tng hp. Trong qu trnh ni suy kt qu l kh nng khi

phc ca bng lc l khng cao. gim mo cho h thng trong qu trnh

phn tch v tng hp, mt s trng thi phn tch b hn ch. V d2 trng

thi phn tch trong MC3D-FSSQ cho phn gii m ho SIF. Ch mt trng

thi c s dng trong ng dng HDTV.

Hnh 2.3.Lc phn tch b chuyn ng vi im nh chnh xc.

(a) Mt cp khung lin k (b) Phn tch tn hiu Video(A: khung trc . B: khung hin thi.

Lt: th thi gian ca u ra thng thp.

Ht: th thi gian ca u ra thng cao.)


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Mc d, b m ho b chuyn ng MC-DPCM c la chn cho

bng lc thng thp theo thi gian trong MC3D-FSSQ, v tr bit vn khng th

ti u ho y cho m ho nhm GOP. Trong h thng mi khng quan

tm n vic khi phc li, chui nh u vo c phn tch thnh 4 trng

thi theo thi gian s dng cho bin i ngc bng lc 3 chiu.

Nhm nh gm 16 khung hon ton khng cha bt k cu trc m ho

no. Do khi thng tin th, ngi ta c th ti u ho trong vic phn chia

bit trong n v d liu ca mi nhm nh trong trng hp mo nh.

2.1.2. Thut ton

Mc ch chnh ca bin i ngc bng lc b chuyn ng (IMCTF)

l khai thc li nh t phn gii im nh trong ngun Video. l chng ta

c th ly mu vi mt dy c nh u vo lin tc ngay khi vct trng

chuyn ng cha p ng c vc t lin quan n chuyn ng trong li

ly mu. N da trn s quan st li nh t ca 2 khung an xen st cnh

nhau v ghp 2 khung phn gii v khng gian sau khi b im nh chnh xc

trong c tnh qut Videobi vct b chuyn ng 1/2 im nh.

Phn ny bt u vi m hnh ph bin cho 2 nh dng: qut xen k v

qut lu tin. Thut ton s thc hin qut lu tin vi 1/2 im nh trn vct

u vo. Thut ton thch nghi cho m ho Videothc s c trnh by cui

cng.

2.1.2.1 M hnh Video ph bin

M hnh ph bin trong mt phng Video c gii thiu bi vct

chuyn ng ton cc (vx, vy).

Cng tn hiu Videoc biu din theo cng thc:

0( , , ) ( . , . )c c x yS x y t S x v t y v t = (2.1)

( . , . ,0)c x yS x v t y v t = (2.2)

V tn hiu ly mu Videoc biu din:


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S[m, n, k] =Sc(VN) (2.3)

y V ma trn ly mu vung 3x3 v N = [m, n, k]T.

Nu tt c cc khung ca tn hiu Video ly mu

c sp xp theokhung tham chiu, im nh trong li con ca khung tham chiu c th c

lp y trong khung ly mu t v tr li ging nhau ca cc khung khc sau

khi b chuyn ng. Chnh v vy, kh nng phn gii nh cao t a khung

ph thuc vo li ly mu v vct chuyn ng ton cc.

Hnh 2.4.Li ly mu cho tn hiu Video xen k

(a) Ly mu ca tn hiu Video theo 2 chiu(y, t)

(b) Khng gian ly mu ca 2 trng st cnh nhau.

V d, xem xt tn hiu Videoan xen trong m hnh (2.1) vi vct

chuyn ng ton cc v = (0, 0), m t trong hnh 2.4 theo 2 chiu thi gian v

trc thng ng. Do khng gian ca li ly mu gm 2 trng chn v l an


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xen nhau nhhnh 2.4 (b), mt khung ghp lai vi s phn gii khng gian

y c th c cu trc bi vic kt hp hi ho 1 cp cnh nhau nhsau:

[ ] [ ][ ]

, ,,, ,

m n n chanC m nB m n n le=

(2.4)

yA vB l gi tr chn v l ca 1 cp st nhau v C k hiu l xung kt

hp.

K thut ly mu an xen ny c hnh thnh trong ng dng TV

nhm lm gim tc ly mu ca tn hiu Video.

Tip theo chng ta s xem xt tn hiu Video vic qut lu tin. Nh

minh ho hnh 2.5 (a), khi s hiu chnh v pha sau dc theo vt chuyn

ng, mi im nh trong chui nh c kt ni ti mu ang tn ti trong

khung tham kho.

Hnh 2.5.Minh ho vn tc ti hn trong tn hiu Video

theo nh dng qut lu tin.

(a) Li ly mu ca tn hiu Video vi vct chuyn ng cc b v =(0, 1).

(b) Li ly mu ca 2 khung lin tip sau khi b chuyn ng.


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2.1.2.2. Qut lu tin Video vi vct chuyn ng chnh xc 1/2 im nh

Xem xt qu trnh qut lu tin tn hiu Videovi 1/2 im nh vn tc

khng i, vi bn mu tn ti trong li lattices (mt co) ca 2 khung lin

tip sau khi b chuyn ng ca ton b im nh nhhnh 2.6. Nhng mu

ny gm cc lp:

LpEO: 2dm chn, 2dn l;

Lp OE: 2dm l, 2dn chn;

Lp OO: 2dm l, 2dn l;

LpEE: 2dm chn, 2dn chn;

y ( )( , ) . , .m n x yd d v t v t = l vct chuyn ng gia khung trc v

khung hin ti v t l chu k ly mu.

So snh lp EO trn hnh 2.6 (a) vi Videoan xen hnh 2.4, chng ta

c th thy rng li mt co ly mu trn hnh 2.6 (a) ging nhli ly mu

trn hnh 2.4 (b) co li 0.5 theo chiu dc. Do vic ly mu li ca 2

khung cnh nhau c trn ln sau khi b chuyn ng. M rng biu thc(2.4), chng ta c th xc nh khung C vi s phn gii gp i theo chiu

dc:

[ ] [ ]

[ ]

, / 2 ,,

, / 2 ,m n

A m n n chanC m n

B m d n d n le

=

+ + (2.5)

yA vB k hiu xung trc v khung hin ti. Do im nh b my

s c lp y bi thi gian 0 - gi cho b lc ni suy trong qu trnh

chuyn ng.

gim sai s trong qu trnh phn gii nh, chng ta c th m rng

thut ton dng cho qu trnh qut t an xen n lu tin. Khung ghp ny

c phn thnh 2 knh phn tch bng lc con theo chiu dc (Bng lc


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Daubechies 9/7). u ra thng thp v thng cao ca bng lc c th xc

nh bi:

[ ] [ ] [ ][ ] [ ] [ ]

0

1

, ,2. ,

, ,2.( ) .

tk

t m n

k

L m n C m n k h k

H m n C m d n d k h k

= =

(2.6)

y h0 v h1 l p ng xung thng thp v thng cao ca bin i

Daubechies 9/7.

Khung ghp C c th hnh thnh thng qua LtvHt. Khung A v B c

th bin i o ngc nh biu thc:

A[m, n] = C[m, 2n] (2.7)B[m, n] = C[m - dm, 2 (n - dn)]

Hnh 2.6.Li ly mu ca 2 khung lin tip

sau khi b chuyn ng ca c im nh.

Hnh trn en lpixel ang c x l. Pixel xm v mi tn

ch r hng b lc,(a) lp EO,(b) lp OE,(c) lp OO,(d) lp EE.


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Tn hiu Videovi vct chuyn ng ca lp OE vOO(hnh 2.6 (b)

v (c)), cp li ly mu ca 2 khung st cnh nhau c bin i an xen sau

khi b chuyn ng, nhlpEO hnh 2.6 (a).

Khung ghp lai phn gii 2 mc c th dng li thng qua vic trn ln

1 cp khung st nhau sau khi b chuyn ng. Biu thc (2.5) (2.7) dng

cho vic phn tch v tng hp tn hiu Videotheo ng ngang v cho.

li ly mu nhhnh 2.5, khung ghp lai c phn gii cao hn

trong min khng gian khng th xy dng vi lp vct chuyn ng ny.

Trong trng hp ny chng ta s dng Lt v Ht tnh ton t l b chuyn

ng v sai khc ca khungA vB:

Lt[m, n] = (B[m + dm, n + dn] +A[m, n])/ 2 (2.8)

V

Ht[m, n] = (B[m, n] -A[m - dm, n - dn])/ 2

KhungA vB c th xc 0nh nh biu thc:

A[m, n] = (Lt[m, n] -Ht[m + dm, n + dn])/ 2 (2.9)

V

B[m, n] = (Lt[m - dm, n - dn] +Ht[m, n])/ 2

Ch rng (2.5) v (2.6) l 1 cp phn tch v tng hp Haar.

2.1.2.3. Di chuyn cc b m rng

Mc d m hnh vct chuyn ng khng i thc s c hiu qu

trong vic bt hnh nh ca chui Videonh thc, n cng c th chng minh

tnh hp l trong rt nhiu ng dng Video. Trong thut ton ca chng ta,kch thc bc ca khi thch hp thay i (HVSBM) c thit lp nh

gi b chuyn ng. Kt qu ca trng chuyn ng thng khng thay i

vi mi im nh t khi chuyn ng ging nhau. Do nu vct chuyn

ng cho khi hin thi nm gia cc lp EO, OE, v OO, th sau khi b


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chuyn ng khi ghp lai c th dng li thng qua vic ghp 1 cp khi kt

ni ca khung trc v khung hin thi. Sau vi cc im nh kt ni

connected pixels, lc phn tch tng hp (2.5) (2.7) c th hnh thnh

tng khi theo khng gian c quyt nh bi lp chuyn ng theo m hnh

2.6. Ti khi bin, tn hiu c m rng i xng ra c 2 bn bng lc. u

ra ca bng lc thng thp v thng cao c lu tr ti v trLtvHttng

ng trn li khi c u vo l khung trc v khung hin thi A vB.

Trong hnh 2.7, chng ta c th minh ho biu phn tch theo thi gian ca

1 cp khi chuyn ng kt ni. Vct chuyn ng ca lp EO vi kch

th

c khi b chuyn ng 3x3

c s dng. i vi vct chuyn ng calpEE, biu thc (2.8) v (2.9) c s dng phn tch v tng hp 1 cp

khi chuyn ng. H thng phn tch v tng hp mi s lm gim cho lp

h thng c. Vi cc im nh khng kt ni (Hnh 2.3), phng php tng

t c ng dng nhsau:

Vi phn tch:

Lt[m, n] = 2A[m, n] (2.10)

[ ] [ ] ( ), , , / 2t m nH m n B m n A m d n d = Vi qu trnh tng hp:

A[m, n] =Lt[m, n]/ 2 (2.11)

[ ] [ ], , 2 ,t m n t B m n L m d n d H m n =

Vi

( ),m nd d l mt phn ca vct chuyn ng bn trong.


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Hnh 2.7. Khi m ho Video ca IMC3D-FSSQ.

Hnh 2.8. V d v lc chuyn ng ca khi nh theo thi gian.

Vct chuyn ng ca khi nh tng ng EO vi kch thc 3 x 3.

(a) Mt cp khi kt ni(b) Khi phn tch ghp(c) Khung kt qu Ltv Ht.


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2.1.3. Ba tham s m ho bng con s dng IMCTF

nh gi lc bng lc theo thi gian cho m ho Video, xut

hp l nht bng lc trong h thng m ho Video3 chiu IMC3D-FSSQ vi

khi ging nhau ti b m ho 3 chiu MC3D-FSSQ. Lc khi cho h

thng m ho c th hin trn hnh 2.3. u tin ngi ta phn tch tn hiu

Videov mt thi gian bi h thng phn tch 2 knh b chuyn ng. Bn

trng thi c hnh thnh trn c s tn s bng con thp pht ra nhhm 8

trng thi trn c s 5 bng phn tch nhhnh 2.4. Ba khng gian trng thi

c phn tch theo lc thi gian hon thnh s phn tch bng con 3

chiu.

Bng lc c s dng y l bng lc phn tch tng hp

Daubechies 9/7. Kch thc khi ca h thng thay i (HVSBM) c dng

cho nh gi b chuyn ng. Cc khi ny c chia lm 1/8 khi tng

mn trong vect chuyn ng. Khi chuyn ng c kch thc trong phm vi

t 4x4 ti 64x64. Khi phn chia c dng lm i din chophn tch/m

ho cy 1/4. Tc bit ca vect chuyn ng iu khin bi h s nhn

Lagrange l mv thc hin trong trng thi c chnh sa. Vct chuyn

ng c m ho bi DPCM v m ho s hc; vct m ho ln cn c

dng cho d on.

H thng m ho c phn chia thnh cc khung lin tip trong 1

nhm nh (GOP), ging nh MPEG. Mi nhm nh cha 16 khung-1 l

khung t-LLLL, 1 l khung t-LLLH, 2 l khung t-LLH, bn l khung t-LH, v

tm l khung t-H. Cu trc bng con 3-D trong 1 nhm GOP m t trn hnh

2.5. Tc iu khin cho mi nhm GOP vi bit d tr c biu din bi:

Rg = Ngr / F(bits) (2.12)

Vi Ng: s khung trong 1 nhm nh GOP;

r: tng s tc bit (bits/sec);


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F: tc ca khung (frames/sec).

Bng con/ly mu wavelet/cc h s c lng t ho v m ho bi

trng thi l

ng t ho xc nh (FSSQ) ca bn dch 3 chiu. Trong thutton lng t ho thch nghi, mi mu trong bng con c phn loi thnh 1

vi lp kch hot da trn vic gii m h s ca bng cha.

Cc mu ring l c lng t ho bi vic hnh thnh cc ngng

(UTQ) vi min cht trung tm, v s dng m hnh hm Laplacian. Bit cp

pht nm trong lp 3-D c ti u ho bi thut ton BFOS, miu t trong

bng 2.1 so snh gia chun IMC3D-FSSQ v MC3D-FSSQ. S khc nhau c

bn gia 2 h thng m ho t

c trn c s l

c lc bng con. Tuynhin nh cp trong mc 2.1, khung t bng thp nht c m ho lin

tip bi b iu xung m DPCM trong MC3D-FSSQ. Ni mt cch khc,

chng ta c th hon ton loi tr dtha thi gian DPCM trong h thng mi

IMC3D-FSSQ vi chi ph v b nh va phi.

2.1.4. Kt qu thc nghim

Hnh 2.9.Nhm 8 trn c s phn tch 5 bng con theo thi gian


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Hnh 2.10: Cu trc bng con 3 chiu trong GOP

IMC-3DFSSQMC-3D

FSSQ

Bng lc theo thi gian IMCTF MCTF

Cu trc lai No Yes

S khung trong mt nhm nh 16 16S trng thi phn gii thi gian 4 2

Tc khung ti a trc khi phn tch theo

thi gian5 3

Kch thc b nh m 16 frs 4 frs

Kh nng ti u ho tc bit cho nhm

nhYes No

Bng 2.1.So snh gia IMC3D-FSSQ v MC3D-FSSQ

Trong mc ny, chng ta s nh gi vic m ho lc phn tch

tng hp IMCTF. Phn mm ny c ng dng bi h thng m ho bng

con mi IMC3D-FSSQ. Kt qu c so snh ti b m ho bng con MC3D-


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FSSQ. H thng m ho mi bao gm cc thnh phn ging nhau MC3D-

FSSQ c so snh hp l. Kt qu m ho s dng chun lai MPEG-2 cng

c tham kho. Kch thc nhm nh cho MPEG-2 c chn l 15 khung

IBBPBBPBBPBBI. Phm vi nh gi xut cho khong cch ca khung thi

gian l 7pixelstrn 1 khung. Videodng th nghim lMobile Calendar,

Flower Garden vFootball trong phn gii SIF (qut lu tin, 352 x240 im

nh, 4: 2: 0, 30 khung/s) c dng nh gi. Mi Videocha 96 khung.

Gii hn c xc nh vi b lc MCTF vic phn tch tng hp khng

c kh nng bin i ngc, khi b lc b chuyn ng thc hin vi chnh

xc 1/2 im nh. Trong qu trnh thc hin, gi tr ca im nh ti v tr l

ic ni suy s dng 8 nc b lc FIR. Bng 2.2 cung cp kt qu nh gi

trung bnh PSNR cho cu trc Videosau khi phn tch sai khc trng thi s

dng chnh xc 1/2 bc sngMCTF m khng m ho.

Bng 2.2.Mo trung bnh PSNR (dB) gii thiu bi chnh xc 1/2 im nh

MCTF vi mc phn tch tng hp khc nhau (cha m ho)


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Hnh 2.11.nh gi khung Y-PSNR cho cu trc lin tip

Mobile Calendar s dng b chnh xc 1 na im nh

ca mc phn tch theo thi gian(cha m ho)

Hai thut ton lc bng con u c th trnh nhiu. Bng lc thi gian

Haar khng b chuyn ng c s dng trong ng dng m ho Video. B

lc b MCTF c th bin i ngc khi bng lc b chuyn ng c thc

hin vi ton b im nh. Bng 2.3 cho bit kt qu so snh h s m ho 3

chiu ca bng lc 3 chiu s dng 2 lc bng lc phn tch tng hp

wavelettrong IMCTF.

Tc m ho c tnh ton theo t l ca phng php i s v hnh

hc ca h s 3 chiu n v dB.


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Video IMCTF TF MCTF-F

Mobile Calendar 11.98/0.0 7.69/-4.29 10.74/-1.23

Flower Garden 13.04/0.0 7.64/-5.40 12.16/-0.88

Bng 2.3.So snh l thuyt m ho 3 chiu (dB) gia 3 lc bng lc

c th bin i ngc: lc b chuyn ng mi (IMCTF),

lc khng c b chuyn ng (TF),

v lc b chuyn ng vi ton b im nh (MCTF-F)

2.1.5. Tm tt v kt lunTrong chng ny mt h thng phn tch tng hp mi vi chnh

xc 1/2 im nh b chuyn ng c pht trin cho ng dng m ho

Video. Kt qu cho thy h thng m ho bng con IMC3D-FSSQ ch

hiuqu hn v c th chun m ho lai MPEG-2.

Hnh 2.12. So snh gi tr trung bnh Y-PSNR cho IMC3D-FSSQ,

MC3DFSSQ, v MPEG-2


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Hnh2.13.So snh Frame-by-frame Y-PSNR cho m ho

Mobile Calendar at 1.0 Mbps.(Average Y-PSNR: IMC3D-FSSQ, 26.74

dB;MC3D-FSSQ, 26.09 dB; MPEG-2, 23.71 dB.)

Bng 2.4.So snh gi tr trung bnh PSNR

cho IMC3D-FSSQ,MC3D-FSSQ, v MPEG-2 (dB).


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2.2. M ho scalable video

Chng ta bit, nn nh l k thut da trn c s m ho bng

con/wavelet

vi vic b chuyn ng cc b

c trnh by trong ch

ngtrc cho ng dng m ho Videononscalable. Chng ta c th thy c u

im ca m ho bng con 3-D l chng minh kh nng loi tr cu trc

khung qui ca b m ho lai. V th m nhng hm u vit nhl phn gii

c cung cp d dng. y bng lc b chuyn ng MC 3-D c kt hp

vi thut ton m ho mt phng bit 3-D EZBC. l s m rng ca thut

ton 2-D EZBC i vi m ho scalableVideo. Ta s gi h thng m ho

ny l IMC3D-EZBC. u im ca b m ho Videogm:

Khc vi b m ho DCT thng thng, bng con phn tch c thc hin

vi ton b nh. Kt qu cho thy vic khi phc nh trong IMC3D-EZBC

khng c li dtha nhm ho DCT.

Kh nng khi phc li khi thc hin cu trc bng con 3-D rt cao, trong

li pht ra do IMC3D-EZBC c gii hn bi chiu di ca b lc

tng hp. y l u im vt tri ca b m ho ny.

Tnh ton n gin: Bng con 3 chiu c m ho nhanh trong h thng

s dng m ho mt phng bit EZBC. So vi phng php truyn thng,

vic tit kim trong tnh ton c th t c vi b m ho b chuyn

ng IMC3D-EZBC m khng cn khi phc li khung tham kho nhm

ho DPCM. phc tp ca h thng m ho khng c tnh i xng do

yu cu v chi ph tnh ton cho vic nh gi chuyn ng ca b m ho.

iu ny hon ton hp l vi mc ch gii m lung bit nhiu ln vi

nhiu mc khc nhau.

Hiu qu nn: Vi h thng bng lc 3-D c b chuyn ng, s dtha

trong Videogim c ng k. S tng quan s c khai thc mt

cch hiu qu khi m ho mt phng bit 3-D EZBC. Kt qu thc nghim


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ch ra t s PSNR ca h thng m ho theo chun MPEG-2 v b m ho

nonscalable3-D.

Tnh mm do v kh nng chuyn su ca lung bit c nh gi ng

ng vi m ho nh EZBC. l h thng m ho scalableVideoiu

chnh vi hm c rng thay i rt rng vi c tnh bm sinh trong a

phn gii v d on 3-D. y l nhng c tnh ni bt c cung cp m

khng xy ra tn tht thng thy trong cc ng dng m ho truyn

thng.

Chng ny c t chc nhsau:

Tng qut v cc cng vic lin quan n m ho scalableVideo. Tip cn a mch vngtrong h thng lai thng thng

Mt vi thut ton bng con v tnh cht r nt (FGS) ca k thut m

ho.

Thut ton m ho.

H thng m ho v cc kt qu m ho

Kt lun

2.2.1. Khi qutM ho scalable c cp n trong cc thp k trc. Ngi ta

sm quan tm tp trung vo tnh tng thch m ho v m ho cho ng

dng thp. y l lp c s ca Video, bao gm cc lung bit con cho ng

dng u cui cao, ging nhchun TV (STV) trong tn hiu HDTV. M ho

scalable c dng trong truyn Videoth thng qua knh c li. tin

cy truyn dn cng cao th chin lc bo v cng phi ci thin trong lung

bit c s m cha thng tin c ngha. Mt vi hm scalablec dng trongchun MPEG-2 v phin bn 2 ca H.263. Chng ta s khi qut li lc

m ho scalablethc hin trong h thng m ho lai.

Ta bit intnet hnh thnh v pht trin rt nhanh t nhng thp k

trc. Mt c trng caInternetl c bng thng thay i theo thi gian v


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ngi s dng. Phng php tip cn a lp thng thng ch c th ng dng

cho lung bit ri rc. Hn na, s lp v mc ca tc bit c m ho ng

thi trong 1 thi gian. V nhvy, gii hn bng thng thay i cho lung

Videokhng th tho mn trong trng hp ny. gii quyt vn ny, k

thut m ho mi SNR c a vo s dng trong chun MPEG-4, chng ta

s phi xem xt li lc m ho FGS trong khung m ho lai truyn thng.

Do c tnh c bn ca h thng m ho lai truyn thng, cc chc nng

thm vo hu nhy t hiu qu vi li c bn trong vic nn. y l tr

ngi chung trong h thng m ho lai.

2.2.1.1. M ho lai truyn thng

2.2.1.1.1.M ho Scalable SNR

Khung m ho truyn thng ni chung khng thch hp trong ng dng

tc m ho mc d n rt gn vi mch vng DPCM. Hnh 2.14 minh ho

lc khi SNR cho h thng m ho lai. Khi lung Videoc gii m ti

lp c s, tp trung cc tn hiu u vo tri ngc nhau hoc cc sai khc

giam ho v gii m theo kt qu ca cc khung tham chiu s dng cho don, ging nhkt qu ca DPCM vi d on mch vng h. Cu trc b

gii m A set of decoding c xc nh trong chun MPEG-2 cho m ho

SNR scalable. Cht lng km trong MPEG-2 ch yu do sai s.

gim sai s gi b m ho v gii m, chng ta c th dng nhiu

mch vng d on phn chia cho cc lp ring l. Cu trc b gii m mi

da trn phng php ny c thm vo cho phin bn 2 ca H.263. Trong

lc a mch vng, nh ca lp c bn c tin on da trn vic s

dng nh ca lp trc . nh ca lp hin thi trong lp tng cng c d

on bi nh ca lp thp hn ngay ti thi im hoc kt hp c hai nh

hnh 2.15. Chng ta c th m bo rng c b m ho v gii m u c th

s dng d liu cho lp hin thi. Nhiu lp tng cng thm vo mc ch


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cung cp cho mc v la chn bit. Ngc li gi ca bin i/lng t ho

ngc v nh gi/b chuyn ng cung cp vi mi m ho mch vng thm

vo khng c hiu qu. Trc ht do nhiu thng tin tiu v khng hiu

qu ca h s lng t ho v m ho li, li trong vic thc hin nn c

quan tm ch yu cho c 2 lp ca h thng m ho. Vn nay c phn

tch trong chun MPEG-2 v H.263.Mt mt nn t 1.0 1.5 dB trn 1 lp.

Hnh 2.14.Lc khi chung ca h thng m ho lai Video SNR

s dng cho d on mch vng.


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Lp gii m tng cng(nt t) l tu chn thm vo tu tng phin bn.

Sai s xut hin khi lp tng cng b loi b.

Hnh 2.15.Lc khi chung cho h thng m ho lai Video SNR

s dng nhiu mch vng d on


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Lp gii m tng cng(nt t)l tu chn.

2.2.1.1.2 Phn gii m Scalable

Phn gii m ho scalableVideoin hnh thng dng biu hnh

kim t thp: Lp c s u tin t c nh m ho 1/10 ngun Video. Khi

phc li lp Videothp hn nh ni suy d on da trn vic phn gii Video

cao hn tip theo. Lp tng cng ch cha tn hiu m ho d on li. V d,

chng ta c th minh ho khng gian v thi gian m ho trong chun H.263

hnh 2.16. Lc phn gii ny c hiu qu v phc tp cho m ho a

mch vng SNR. Trong trng hp ny, gi tr PSNR l 1.34 dB v trong

tng lai c th loi bt 0.471.38 dB.

Hnh 2.16.Minh ho m ho phn gii scalable trong H.263.I, P, v B

i din cho nh I, P v B trong chun H.263.nh t nt

lin quan ti lp m ho tng cng.

2.2.1.2. Embedded Coding and Fine Granularity Scalability

Nh nhng thnh cng trong vic nn nh trong nhng nm gn y

em li nhng xut v thc hin m ho nh cho m ho DFD trong h

thng m ho thng thng. Ngc li do nhng mch vng DPCM trc kia,


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lung bit Videokhng th gii m ti tc bit thp hn do tn hao. Chnh v

vy mc d b m ho vn tha k mt vi c tnh u vit nhn gin, iu

khin tc bit chnh xc t vic xy dng hnh nh m ho kh nng SNR

trong vic thc hin m ho vn phi loi b.

tho mn yu cu pht trin cho Videoa tc vi tnh cht kt

dnh cao v khng b nh ng do sai s, mt vi thut ton st nhp m ho

mt phng bit trong khung m ho lai truyn thng c gii thiu. Trong

chun MPEG-4 FGS, khung tham kho trong mch vng DPCM c gii m

t lp bit c s, tng ng vi bin di ca phm vi m ho Video. Phn cn

li sau khi bin i DCT

c m ho bi mt phng bit DCT, nh

Hnh 2.17.Do lp bit c s lun c kh nng gii m (gi thit khng c tn hao), s sai

khc gia b m ho v gii m hu nhkhng xy ra.

Qu trnh gii m c th dng ti bt k im n khi lung bit c gii

m thnh cng. Lc mch vng n cng c chp nhn bi 1 vi b m

ho a lp SNR lm gim phc tp vi mch vng vi phn c thm

vo.

Tuy vy so snh vi l

c a mch vng hnh 2.15, ph

ng php tipcn bn ngoi khng phi l vic s dng thng tin ti u nht cho gii m,

cn thy mt thc t rng b gii m lun s dng hnh nh cht lng km

nht trong mch vng DPCM trong ton b phm vi m ho.

Nhchng ta bit d on li khc nhau gia tng vi s suy gim

tc bit. Do PSNR thng mt 2 dB khi so snh vi vi phng php

nonscalabletng t. Kt qu ch ra rng mch vng s c th ti hn chng

trnh ti tc bit cao. Chnh v th phm vi bit b gii hn. Khung mchvng n cng c thit lp bi Shen v Delp trong vic kt hp vi b m

ho EZW.


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Mt vi xut nhm ci thin hiu qu nn nh trong ch FGS ca

MPEG-4. Tuy nhin do gii hn ca vic m ho lai, vic ci thin thut ton

cn nhiu gii hn.

Hnh 2.17.Lc khi chung ca h thng m ho lai Video

cho vic cung cp chc nng FGS


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Lp m ho tng cng(nt t) l tu chn.

2.2.1.3. M ho s dng bng con 3 chiu v m ho Wavelet

Mc d khng c kin phn hi ca mch vng DPCM, cu trc m

ho bng con 3 chiu hon ton ph hp cho m ho SNR scalable. Vi vic

quan tm trong ng dng a tc , mt vi thut tonthc hin m ho bng

con 3-D c xut trong cc ti liu gn y. Khng ging nhb m

ho thng thng, SNR trong h thng m ho nyt c vi s mt mt m

ho khng ng k. LZC (LayerZero Coding) v 3D-SPIHT (SetPartitioning

InHierarchical Tree) l 2 phng php m ho in hnh trong m ho 3-D.

LZC do Tubman v Zakhor thit lp gi tr u tin trong my tnh dng cho

m ho Video a tc 3 chiu. Vi hiu qu ln trong vic khai thc s

tng quan gia gi tr cc bng con, LZC ch r 1 trong nhng u im

ni bt ca PSNR cho nh nn. ng dng trong m ho Video, chng ta s

xem xt nh hng chuyn ng ca ton b camera. Chui nh c tin lm

mo, hoc sp thng hng, trc khi phn tch bng lc nhm trnh cho nh b

blurring. Ba tham s SPIHT ny l s m rng trong m ho nh SPIHT. Bin

i bng lc Daubechies 9/7 ph bin c thc hin trong mi tham s

pht sinh cu trc bng con 3-D. Thut ton ny c thc hin nhm mc

ch khai thc 1 nhm h s bng con 3-D/wavelet. Cu trc cy trong h

thng 3 chiu c dng cho vic nh gi h s khng quan trng. c tnh

n gin ca SPIHT c gi li. Lung bit m ho l tc bit m ho v

c thc hin y . Mc d c rt nhiu cng vic cng b trong min nn

nh Video, hu ht cc thut ton u da trn bng lc 3-D c in (khng c

b chuyn ng). Thm ch c chuyn ng ton cc. Khng nhcc phng

php m ho lai truyn thng, thng tin v chuyn ng cc b s c st

nhp trong h thng m ho bng con 3 chiu. Tuy nhin nhchng ta nhn


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mnh trc , hiu qu cht lng nn Videoda vo vic khai thc thng tin

v chuyn ng. Do cc thut ton ny khng th cnh tranh vi b m ho

lai truyn thngtrong nn nh cho tc bit n (nonscalable) ng dng khi

chuyn ng tc cao tn ti trong ngun Video. iu ny c chng minh

trong kt qu thc nghim s tho lun sau. Mt trng hp ngoi l ng ch

l xut cy Tri-Zerotree a ra bi Th cho m ho tc bit thp. Tuy

nhin bng lc xut ny khng c kh nng bin i ngc v khng l

chun cho ng dng m ho Video.

2.2.2. H thng tng quan

Hnh 2.18.Lc khi ca h thng scalable Video.

Mc ch thc hin ca h thng m ho Videoc th hin trn Hnh

2.18. Tn hiu Videou vo u tin c bin i nh 3 tham s b chuyn

ng bin i ngc gioi thiu trong chng trc. So snh vi khng gian

v thi gian bng lc truyn thng (khng c b chuyn ng), bin i 3-D

c th loi b d tha v khng gian trong tn hiu Video trong trng thi

chuyn ng cao. Kt qu l khng gian thi gian bng lc 3- D v cu trcnhm nh ch ra trn hnh 2.9 v 2.5. Bit d tr chonhm nh ring c a

ra bi hnh (2.12) cho tc m ho bit khng i (CBR).

H s ca bng lc 3-D ri sau c m ho bi thut ton m ho

mt phng bit EZBC (3D-EZBC). Tng t nhbn sao 2-D, 3D-EZBC m


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ho cc h s ring l thng qua lng t ho v m ho. Chnh v vy h s

c bin i cho php gii m trong phm vi d on rng vi kch thc

b

c ca min cht 2 .n

= vi n=nmax. . .0 l ch s mt phng bit v lkch thc bc tin lng t ho. H s bin i trong bng con ringc th

sp xp li, t l, hoc khai thc lng t trc khi m ho mt phng bit cho

mc ch iu khin tc ... Thut ton m ho mt phng bit 3D-EZBC s

c gii thiu trong chng sau.

Lung bit m ho dng cho ng dng ph thuc trng thi nh dng

nn. Do tt c cc khung trong cng 1 nhm nh c x l v m ho ng

thi, nn cn b m khung Ng, y Ng l s khung ca nhm nh nhnc. Tr ln nht quan h gia 2 khung u cui 2Ng - 1 chu k khung.

Trong h thng gii m, hot ng bin i ngc c thc hin ngc li

m ho m khng cn b chuyn ng. Mu ca bng con gii m c cu

trc bi mu tng t - ph thuc vo vic thc hin thut ton lng t ho

trong b gii m nh EZBC.

iu ng ni l khng ging nhh thng m ho lai truyn thng, b

v nh gi chuyn ng trong hnh 2.18 c hnh thnh trn c hai tn hiuu vo gc. Mch vng phn hi DPCM v cc quan h khc khng c

gii thiu trong h thng m ho Videony.

2.2.3. Bng con m ho 3 chiu

Thut ton m ho mt phng bit 3D-EZBC c m rng trc tip ca

thut ton 2 chiu 2-D EZBC ti cc khung ring l trong h thng bng con 3

chiu m t trn hnh 2.5. Cy 1/4 u tin c thit lp cho bng con ring

l t khung nhn c. Gi tr ca nt cy 1/4 Qk(i, j, t) ti v tr (i, j, t), mccy 1/4 l l v bng con k c xc nh nhsau:


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( ) ( )

( ) ( )

Q 0 (i, j,t) c (i, j,t)k k

Q l -1 2i,2j,t ,Q l -1 2i,2j + 1,t ,k kQ l (i, j,t) max

k Q l -1 2i+1,2j,t ,Q l -1 2i+1,2j+1,t k k

(2.13)

vi ck(i, j, t) l gi tr bng con ti v tr (i, j, t), vi bng con th k. Vi vic

xy dng quy cy 1/4, nt nh ca cy c gi tr bin ln nht trong tt

c cc mut bng con ging nhau trong khung nhn c. Nt nh ca cy

bao gm LIN ti qu trnh bt u ca mt phng bit.

D liu trn mt phng c m ho t mu c ngha ln nht MSB n

mu t c ngha nht LSB nh kim tra cc nt t LIN v tinh chnh h s t

LSP. Chng ta c th thc hin ging nh trong m ho 2-D EZBC chovicm ho entropyca mt phng ly mu. Th tc hon chnh c th tm tt

nhsau:

nh ngha

m(i, j, t): bit c ngha nht (MSB) ca nt (i, j, t).

Dk: su ca cy 1/4 cho bng lc k.

Dmax: max{k}{Dk}.

K: tng s bng con.

n: ch s ca mt phng bit thng qua hin thi, tng ng vi

ngng lng t ho 2n.

Sn(i, j, t): nt kim tra c ngha (i, j, t) i din vi ngng 2n,

( )

0), gim n quay li bc 2.

M gi:CodeLIN (k, l)

{

for mi nt (i, j, t) trong LINk[l]

- M hoSn(i, j, t)

- Nu (Sn(i, j, t) = 0)

* Duy tr phn cn li (i, j, t) trong LINk[l]

- ngc li

* Nu (l = 0), m ho bit du ca ck(i, j, t) v thm nt (i,

j, t) ti LSPk

* ngc li CodeDescendants (k, l, i, j, t)

}


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CodeDescendants (k, l, i, j, t)

{

for mi nt (x, y, t) trong { (2i, 2j, t),(2i, 2j+1, t),(2i+1, 2j, t),(2i+1,

2j+1, t)}ca mc l-1 trong cy 1/4, bng k

- M hoSn(x, y, t)

- Nu(Sn(x, y, t) = 0), thm nt (x, y, t) vo LINk[l - 1]

ngc li

-Nu(l = 1), m ho bit du ca ck(x, y, t) v thm nt (x,

y, t) vo LSPkngc liCodeDescendants (k, l - 1, x, y, t)

}

CodeLSP (k)

{

for mi im nh (i, j, t) trong LSPk

- m ho bit n ca|ck(i, j, t)|

}

2.2.4. T l dng bt m ho

Tip theo chng ta s xem xt cch nn lung bit m ho t b m ho

c th t hiu qu chu cc ng dng m ho Videothay i.

2.2.4.1.H thng dng bt

Ging nhc cu ca mt phng m ho bng con 3 chiu/waveletca

tn hiu Videovi tc chuyn ng ca khung. Trong trng hp ny bng


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con lc 3 chiuch ra trn hnh 2.10, thi gian phn tch Rt= 4 vi khng gian

phn tch Rs= 2, kt qu l tn hiu Videoc phn thnh 5 bng li mt

co theo thi gian v 3 bng l

i theo khng gian minh ho trn hnh 2.19.Bng con m ho c tin lng t ho vi bc lng t c gii m vi

phm vi lng t ho hiu qu n2 . ,n n ,...,0max = = , bi mt phng gii

m bit n.

Hnh 2.19.Tn s phn gii bng con bin i tn hiu Video 3-D

trong h thng m ho Vieo

Nhm nh ring phc v cho n v m ho c bn cho vic hnh thnh

iu khin ca lung bit t l. Th bc ca lp bit m ho trong nhm nh

c m t trn hnh 2.20.

Trn cng ca h thng m ho, ch ra trn Hnh 2.20 (a), mi nhm

nh m ho gm 1 n v lung bit c lp {PMV, PY, PU, PV}, yPMV

k hiu lung bit cho trng chuyn ng, v PY, PU,PV l h s bng con

p ng vi thnh phn mu Y, U, V ca tn hiu ngun Video.

Lung bit chuyn ngPMV gm lung bit nh hn {PMV rt|rt=1, . .

., Rt} lin quan ti vect m ho b chuyn ng cho bng lc b chuyn ng

trong biu t l thi gian rt, minh ho trn Hnh 2.20 (b). H s lung bit


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PVc to ra t s la chn bng con { 0, . . ., Rs} lin quan ti h s m ho

bng con t khng gian t l (rt, rs) v thnh phn mu v{Y, U, V }, minh

ho trn Hnh 2.19 v 2.20 (c). Trong tt c cc lung bit con ,t sv

r rP c m

ho t MSB n LSB v mi mt phng bit n thng qua s c phn chia

thnh cc mt phng bit conl. Lp h thng cho h s lung bit bng con

,t s

v

r rP c cung cp trn Hnh 2.20 (d), y ,t sr rK l s bng con t l (rt, rs)

v Dmax v nmax nh ngha trong mc 2.2.3. Dmax = 9; nmax = 12 (vi =


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n cao hc TVT 2003

Nguyn Hu Pht 77

1) l tham s in hnh cho phn gii SIF (mc 2.5).

Hnh 2.20.Lp h thng file lung bit pht sinh trong h thng

m ho Video scalable EZBC.(a) nh h thng.(b) La chn lung bitcon chuyn ng(c) La

chn h s lung bitcon cho thnh phn mu v.(d) Lp h thng cho lung

bitcon quan h n khng gian t l(rt, rs).


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Nguyn Hu Pht 78

2.2.4.2. La chn dng bt m ho v truyn dn

Ging nhthut ton m ho mt phng bit 2 chiu 2-D EZBC, ch

c bit nhn c cho m hnh h s bng con 3 chiu trong h thng m

ho Videov th lung bit phn gii thp hn c th gii m m khng cn

phn gii bng con mc cao hn. Lung bit bng con trn Hnh 2.20 c

m ho theo t m s hc c lp v c a vo a ch ho trong 1 file. Kt

qu l chng ta c th chn bt k thnh phn vmu no ca tn hiu Video

m ho khi phc li trong s phn gii khng gian khc nhau, tc khung

v mc cht lng, (Rt, Rs, Qn), nh s la chn n v m ho

{ },, max, 0 ' ,0 ' , 't t sMV v n

r r r t t s sP P r R r R n n n .

Vi nhm 8 tn s phn chia trong c khng gian v

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