X l tn hiu sGVHD Th.s Nguyn Thu Hin

HC VIN CNG NGH BU CHNH VIN THNG KHOA VIN THNG 1

TIU LUN nh x khi Block MatchingHc phn:X l m thanh v hnh nh

Ging vin:Ths.Nguyn Thu Hin

Nhm sinh vin

Nguyn Quyt Tin Nguyn Hu cPhm Quang nh

Lp:D11VT3

H Ni, thng 10 nm 2014.

Li ni u Cng ngh x l nh ngy cng pht trin v c ch trng, cht lng nh v video ngy cng c nng cao p ng nhu cu trao i thng tin ca con ngi. Ti liu ca chng ti ch yu tp trung ni v phn x l nh trong phng php m chng ti mun ni ti v nghin cu y l vn nh x khi. hiu c tm quan trng ca n cng nh li ch ca vn ny mang li ta s cng nhau tm hiu n. Bng cch loi b d thiu trong nh s tip kim s bits dnh cho m ha v s tit kim c bng thng trn mi trng internet qua thy c tm quan trng ca vn ang nghin cu. Lm cch no ta nh gi s chuyn ng ca video, khi truyn trn ng truyn ta truyn ci g v nh th no nhng cu hi s dn c gii p qua ti liu nghin cu ca chng ti. V thi gian c hn nn s khng th trnh c nhng sai st mong c gi v cc bn gp hon thin hn ti liu nghin cu ca chng ti. Nhm tc gi

Nguyn Quyt TinNguyn Hu cPhm Quang nh

H Ni thng 10/2014

Li ni u2Bng biu v hnh nh41.Gii thiu tng quan51.1 nh x khi71.1.1 Khng chng ph, cch u nhau, c nh kch thc , nh x khi vi kch thc ch nht nh81.1.2 Tiu chun nh x101.2 Thut ton nh x khi121.3 Th tc tm kim131.3.1 Tm kim y 131.3.2 Tm kim logarit-2D141.3.3 Thut ton tm kim ba bc171.3.4 Thut ton tm kim ba bc mi191.3.5 Thut ton tm kim bn bc211.3.6 nh x khi a phn gii221.3.7 Ngng a phn gii nh x khi251.4 Hn ch ca k thut nh x khi301.5 Ci tin mi311.5.1 Cu trc phn cp nh x khi311.6.2 Li a trong nh x khi351.6.3 nh x khi qua OVERLAPPER392.Kt lun.413.Ti liu tham kho42

Bng biu v hnh nhHnh 1. 1 nh x khi9Hnh 1. 2 Ca s tm kim v ca s tng quan.10Hnh 1. 3 nh x khi ca mt macro block c cnh bn l 16 pixel v tham s tm kim p c kch c l 7 pixels.12Hnh 1. 4: Phng php-2D tm kim logarit.Ti im (j;k+2),(j+2;k+1),(j+2,k+4) v (j+1,k+4) da trn s ti thiu cc im khc nhau trong tng bc 1,2,3 v 4 ring tng v tr.15Hnh 1. 5 Phng thc tm kim logarit 2D.Ti im (j,k-2),(j+2,k-2) v (j+2,k-1) l da trn s ti thiu cc im khc nhau trong bc 1,2,3 v 4 ring tng v tr.16Hnh 1. 6 Phng thc tm kim 3 bc.im( j+4,k-4) ,( j+4 , k-6 ) v ( j+5,k-7) cho cc im ti thiu khc nhau trong bc 1 ,2,3 ring tng bc.17Hnh 1. 7 Qu trnh tm kim 3 bc. Vector chuyn ng l (5,-3)19Hnh 1. 8 nh x khi tm kim 4 bc.20Hnh 1. 9 Qu trnh tm kim 4 bc. Vecto chuyn ng l (3, -7)22Hnh 1. 10 Mt v d v 2x2 mu ph trong khi v s tng quan ca s ban u cho tm kim nhanh.23Hnh 1. 11 Cu trc kim t thp gauss.25Hnh 1. 12 S khi ca nh x khi a phn gii ngng ba mc27Hnh 1. 13 X l ngng29Hnh 1. 17 Minh ha 3 mc ca cu trc phn tng35Hnh 1. 17 S thut ton a li nh x khi.37Hnh 1. 18 To ngng a li nh x khi.38Hnh 1. 19 Overlapped block matching.39

Bng 1. 1 Cc thng s c s dng trong 3 mc ca kin trc phn tng nh x khi33

1.Gii thiu tng quanVi s tin ti th h a phng tin v s tri rng internet, ti nguyn d liu video trn CD/DVD v dng video dnh c nhiu s a chung.Trong c hai tiu chun c bn lu lng ton b qu trnh nn-gii nn l ging nhau v miu t trong hnh 1. M ha c lng trn kha cnh chuyn ng trong khung hin ti vi cc quan h ti khung trc. Mt nh b chuyn ng ca khung hin ti to nn khi ca nh t khung trc . Vector chuyn ng ca khi s dng c lng chuyn ng c truyn i.M ha nh gi i sau gii m ,m ha s dng khung tham chiu.Tt c tng ng sau c lng chuyn ng da trn nn video ti tit kim bits, khc bit khi dng t nng lng v c th nn cao so vic vi gi mt khung y JPEG khi c m ha.

Hnh 1: MPEG/H.26x tin trnh nn video.

Motion JPEG, tt c khung JPEG c m ha, t mc ch gia 10:1 n 15:1 t l nn, MPEG c th t t l nn 30:1 vn s dng t l 100:1 [1] [2] [3]. Ch rng khung u tin lun gi ton b, v vi khung khc c th thng xuyn. Cc tiu chun khng ch nh iu ny v c th thay i vi tt c video c gi da trn hot ng ca video.Cc tnh ton t tin v hot ng thiu ti nguyn trong ton b qu trnh nn l c lng chuyn ng. Bi vit ny thc hin v c lng thut ton nh x khi c bn t gia nm 1980 cho n nm 2002. Cc thut ton c thc hin l tm kim nghin cu ton din (ES),tm kim ba bc (TSS),tm kim bn bc (4SS), thut ton bc mi v thut ton 2D logarit.

1.1 nh x khiMt nh u tin c phn chia thnh cc khu vc vi nhau mt khong cch bng nhau. Sau vector chuyn ng c c lng cho mi khu vc. Phn on v c lng chuyn ng kt hp vi khi khun dng ty l rt kh khn. Khi c nhiu khu vc chuyn ng phc tp trong nh, tnh hnh tr ln kh khn. Thm vo nhng vector chuyn ng, nhng thng tin hnh dng ny trong mi khu vc cn c m ha. K t y, khi khu vc dch chuyn c hnh dng khc nhau, ng thi tnh ton v m ha tng ln ng k.K thut nh x khi c tp trung trong phn ny, n gin, khng phc tp v cn rt hiu qu. Cho n nay c s dng ph bin nht trong k thut c lng chuyn ng trong m ha nh. Trn thc t, n c chp nhn bi cc tiu chun m ha video quc t: ISO, MPEG-1 v MPEG-2, v ITU H.261, v H.263. Chng bao gm khi nim v thut ton, tiu chun ph hp, chin lc tm kim, hn ch, v ci tin mi.1.1.1 Khng chng ph, cch u nhau, c nh kch thc , nh x khi vi kch thc ch nht nhMt nh c chia v tp hp khng chng ph, cch u, c nh kch thc, khi ch nht nh, v chuyn ng tnh tin trong mi khi c gi nh l u nhau. Mc d m hnh n gin coi nh ch l chuyn ng tnh tin, cc loi chuyn ng khc, chng hn nh xoay v phng to trn cc i tng, c th gn nh l dch tng phn theo cc khi nh vi iu kin l cc khi phi nh. Vector chuyn ng cho cc khi ny c c lng bng cch tm cc khi ging vi chng nht trong cc khung cho trc. Theo cch ny, c lng chuyn ng l mt cch d dng nht so vi cc khi hnh dng ty . T dch chuyn mi khi c m t bi vector chuyn ng, thng tin kha cnh vector chuyn ng gim dn.

Hnh 1. 1 nh x khiV li thng tin hnh ch nht c bit c hai b m ha v gii m, v khng cn phi m ha, tit kim ng thi tnh ton v thng tin ph.Kch thc khi cn chn chnh xc. R rng, kch thc khi nh hn dn n nhiu vector chuyn ng c c lng v m ha, trong tng ng thi tnh ton v thng tin ph. Hnh 1.1 l dng minh ha k thut nh x khi.Trong hnh 1.1(a) mt khung nh ti tn l c phn on thnh khung v chng ln khung p x q hnh ch nht. Xem xt mt khi c tm ta (x, y). Gi s khi dch chuyn ton b. Do , ch mt vector chuyn ng cn c c tnh bng khi ny. Hnh 1.1(b) hin th khung trc: khung ti ti tn-1 . c lng vector chuyn ng, mt ca s hnh ch nht c m trong khung tn-1 v tm ti im nh (x, y). Xem xt mt im nh trong ca s tm kim, mt ca s hnh tng quan ch nht c kch thc gn nh l p x q. Bin php tng quan c tnh ton. Sau qu trnh nh x ny c hon thnh tt c im nh ng vin trong ca s tm kim, ca s tng quan tng t ging nhau nht tr thnh cc khi ging nhau hp li nht di s xem xt nh mt khung tn. V tr tng i ca hai khi ny cho vector chuyn ng. iu ny hin th trong Hnh 1.1(b). Kch thc ca s tm kim l xc nh r bi kch thc ca s tng quan v khong cch dch chuyn ti a c th theo bn phng din: trn, di v v pha phi v pha tri.Trong hnh 1.2 bn hng theo gi thit l ging nhau v c biu th l d. Ch rng d l c tnh t mt kin thc tin nghim v chuyn ng tnh tin, trong bao gm tc chuyn dch ln nht c th v khong thi gian gia hai khung hnh lin tip.1.1.2 Tiu chun nh x

Hnh 1. 2 Ca s tm kim v ca s tng quan.nh x khi thuc nh x nh v c th nhn thy t mt gc rng hn nhiu.Trong tin trnh x l nh, chng ta cn phi kim tra hai hnh nh hoc hai phn ca nh trn mt im nh bi mt im nh c s. Mc ch ca vic kim tra l xc nh s ging nhau gia hai hnh nh hoc hai phn ca nh. Bin php ng dng, hoc bin php tng quan, l yu t cha kha trong tin trnh nh x. Php o tng quan c bn gia hai nh tn v tn-1, C (s, t), l vch r nhu sau

(1.1)

y l quy vo nh l mt tiu chun ha chc nng tng quan cho hai chiu.Tnh khng ng dng (i khi quy vo sai s, mo, khong cch) gia hai nh tn v tn-1, D (s, t) l vch r nh sau

(1.2)

Trong M (u, v) l thc o tnh khng ng dng gia hai arguments u v v. D( s, t) l quy vo tiu chun ph hp ca gi tr D. 1.2 Thut ton nh x khi

Hnh 1. 3 nh x khi ca mt macro block c cnh bn l 16 pixel v tham s tm kim p c kch c l 7 pixels.Xt vi khi tm kim l khi vung tng ng sau nh x khi l phn chia khung hnh hin thi thnh mt ma trn macro block, sau so snh vi block tng ng v cc khi ln cn trong khung trc to ra mt vector quy nh s chuyn ng mt macro block t im ny n im khc trong khung trc . Chuyn ng ny c tnh cho tt c cc macro block bao gm mt khung, thit lp d on chuyn ng trong khung hin thi. Vng tm kim tt cho mt macro block ph hp c quy nh ln n p im nh trn bn pha ca macro block tng ng trong khung nh trc . p c gi l tham s tm kim. Chuyn ng cng ln th yu cu p cng phi ln, v ln ca tham s tm kim c tnh ton k qu trnh ny tr thnh d on chuyn ng. Thng thng macro block c cho nh mt vung vi cnh l N=16 pixel vi tham s p l 7 pixels hnh 1.3. Mt macro block c nh x thnh mt block khc da trn gi tr u ra ca mt hm. Gi tr l kt qu thp nht thu c t vic nh x block hin ti gn nht thu c mt macro block mi. Mt hm th c nhiu gi tr khc nhau, trong ph bin nht v c tnh ton k nht l trung bnh sai khc tuyt i (Mean Absolute Difference - MAD) cho bi phng trnh (1.5). Mt gi tr khc ca hm l trung bnh sai s bnh phng (Mean Squared Error MSE) cho bi phng trnh (1.6).

Trong : N l cnh bn ca macro block. Cij v Rij l im nh ca macro block hin ti v macro block qui chun tng ng.1.3 Th tc tm kimVn tm kim l mt vn quan trng i ph vi nh x khi.Mt s th tc tm kim c tho lun di y.1.3.1 Tm kim y Hnh 1.2 : Cho thy mt ca s tm kim, mt ca s tng quan, v kch thc ca chng.Trong vic tm kim ph hp nht, ca s tng quan c di chuyn n tng v tr c th chn trong ca s tm kim. C ngha l, c mt tng (2d+1)x(2d+1) cc v tr m cn c kim tra.S khc nhau ti thiu cho kt qu ph hp nht.R rng, y l phng php tm kim y l mt thut ton trong trng thi t nhin. Tm kim y cung cp chnh xc kh tt trong cc tm kim ph hp nht (Do chnh xc cao trong s c lng chuyn ng ),nhng mt s lng ln cc php tnh l phc tp.1.3.2 Tm kim logarit-2DPphp 2D lin tc gim c din tch vng tm kim, do lm gim c gnh nng tnh ton.Nhng bc u tin tnh ton tiu chun ph hp cho 5 im trong ca s tm kim.Nm im ny l nh sau : mt im trung tm ca ca s tm kim v bn im xung quanh n,vi mt im gia l im trung tm bn ranh gii ca ca s.Bc 1: Trong s 5 im ny , s tng ng mi im c mt mc (cc mc khc nhau) so snh vi mt mc ti thiu v s chn ra im chin thng.Bc 2: Xung quanh im chin thng li c mt b nm im khc li c la chn v li quay li tng t nh bc u tin, vi khong cch gia cc im trung tm v nm im cn li khng thay i.Trong trng hp ngoi l xy ra khi im tip theo hoc l mt in trung tm ca mt b 5 im hoc mt im nm trn ca s tm kim cho mt gi tr D nh nht th khong cch gia nm im cn phi c gim.Phng php c tip tc cho ti bc cui cng , trong mt tp hp cc im c th chn c t trong mt mng li 2D 3x3. Hnh 1.4 v 1.5 gii thch hai trng hp ca phng php.Hnh 1.4 thy c rng gi tr D ti thiu nm trn mt ranh gii ca 5 im, khi hnh 1.5 cho thy rng gi tr D ti thiu nm trong trung tm v tr trng v tr sai lch.

Hnh 1. 4: Phng php-2D tm kim logarit.Ti im (j;k+2),(j+2;k+1),(j+2,k+4) v (j+1,k+4) da trn s ti thiu cc im khc nhau trong tng bc 1,2,3 v 4 ring tng v tr.

Hnh 1. 5 Phng thc tm kim logarit 2D.Ti im (j,k-2),(j+2,k-2) v (j+2,k-1) l da trn s ti thiu cc im khc nhau trong bc 1,2,3 v 4 ring tng v tr.1.3.3 Thut ton tm kim ba bc

Hnh 1. 6 Phng thc tm kim 3 bc.im( j+4,k-4) ,( j+4 , k-6 ) v ( j+5,k-7) cho cc im ti thiu khc nhau trong bc 1 ,2,3 ring tng bc.

Mt phng php ba bc c pht trin tm kim nhanh.Ba bc tm kim tng t nh trong thut ton 2D.Tuy nhin ba bc ny khc 2D chnh l 2 th tc.Th 1 : Mi bc trong vic tm kim ba bc c so snh vi mt tp hp 9 im to thnh mt cu trc li 2D 3x3.Th 2 : Khong cch giu cc im trong cu trc dng li 3x3 2D trong ba bc tm kim s gim n iu trong bc 2 v bc 3.Tng cng ch c ba bc c thc hin.R rng, y l ba bc khc nhau so vi tm kim logarit 2-D c m t trong phn 1.3.2. minh ha cho iu ny ta xem xt v d ca tm kim ba bc nhn trong hnh 1.6 v c th hn ta xt v d sau.V d u tin tm kim ti v tr trung tm v c thit lp step size d = 4.Sau n tm kim 8 im +/- d pixel xung quanh im (0,0). T 8 v tr tm kim c n chn mt im c gi tr thp nht v bin n thnh v tr gc tm kim mi. Sau tip tc thit lp kch thc bc mi d = d/2, ri tip tc tm kim tng t nh trn, lp i lp 2 ln cho n khi d = 1. Lc v tr tm kim c gi tr hm thp nht v macro block ti l ph hp nht. Tnh ton vector chuyn ng ri lu li truyn.Vi p=7, ES s tnh ton gi tr cho ((2*7)+1)2 = 225 macro block trong khi TSS ch tnh ton gi tr cho 25 macro block. Hnh 1. 7 Qu trnh tm kim 3 bc. Vector chuyn ng l (5,-3)

1.3.4 Thut ton tm kim ba bc miNTSS l ci tin kt qu t thut ton TSS bng cch cung cp mt chng tnh tm kim center biased v quy nh cch ngn chn gim gi tr tnh ton. N l mt trong cc thut ton nhanh u tin c cng nhn rng ri v thng c s dng cho vic thc hin cc tiu chun trc nh MPEG 1 v H.261.

Hnh 1. 8 nh x khi tm kim 4 bc.TSS s dng mt m hnh kim tra phn b u pht hin chuyn ng v cc chuyn ng nh b khuyt. Qu trnh NTSS c minh ha bng hnh 1.8. Trong bc u tin 16 im c kim tra tm ra trng s thp nht bng cch s dng mt gi tr ca hm. Nu gi tr ti v tr ban u l thp nht th vic tm kim s dng li ti v vector chuyn ng c mc nh l (0, 0). Nu trng s thp nht bt k v tr no trong 8 im ti v tr d=1, th chng ta thay i v tr tm kim ban u v kim tra cc trng s xung quanh n. Ty thuc vo cc im m chng ta ch kim 5 hoc 3 im (hnh 1.8 (b) & (c)). V tr cho trng s thp nht ph hp nht v vector chuyn ng s c thit t ti y.Mt khc nu trng s tm c l thp nht sau bc u tin l mt trong 8 v tr ti d = 4, th chng ta s tin hnh TSS theo cch thng thng. Do ,qu trnh ny c th cn ti thiu 17 im kim tra mi macro block, nhng n cng c trng hp xu nht ca 33 v tr c kim tra.1.3.5 Thut ton tm kim bn bcTng t nh NTSS, 4SS cng s dng tm kim center biased v qui nh cch chn na chng. 4SS thit t mt kch thc mu c nh ca d = 2 trong bc u tin, khng cn bit gi tr tham s tm kim p l g. V vy, n trng nh 9 v tr trong mt ca s c 5x5. Nu trng s tm c ti trung tm ca ca s tm kim th vic tm kim c nhy sang bc bn. Nu trng s l mt trong 8 v tr ngoi tr trung tm, th ta c v tr tm kim ban u mi v chuyn n bc th hai. Ca s tm kim vn c duy tr nh l mt im nh c 5x5. Ty thuc vo ni c trng s thp nht, chng ta ch kim tra trng s ti 3 hoc 5 v tr. M hnh mu c biu din trong hnh 1.9. Lp li ln na nu v tr c trng s thp nht trung tm ca ca s tm kim 5 x 5 chng ta nhy n bc bn hoc chuyn sang bc ba. Bc th 3 ging y nh bc th 2.Trong bc th t kch thc ca s gim xung cn 3x3, tc l d= 1. V tr vi trng s thp nht c nh x macro block tt nht v vector chuyn ng c thit lp ch a im . Qu trnh ly mu c th hin trong hnh 1.8. y l thut ton tm kim tt nht trong trng hp 17 im kim tra v xu nht trong trng hp 27 im kim tra.

Hnh 1. 9 Qu trnh tm kim 4 bc. Vecto chuyn ng l (3, -7)1.3.6 nh x khi a phn giiXt cu trc Kim T Thp y l mt phng php rt mnh trong cc tc v tnh ton v x l hnh nh khc nhau. tit kim tnh ton trong cc khi ph hp, n l phi nh ti cu trc kim t thp. Trong mt k thut a phn gii c tn l top down, mt kim t thp gauss in hnh c hnh thnh u tin.

(a) Bt u khi 16x16 trong khung ti tn(b) So snh ca s ca 16x16 trong khung ti tHnh 1. 10 Mt v d v 2x2 mu ph trong khi v s tng quan ca s ban u cho tm kim nhanh.Trc khi i su vo m t k hn, Chng ta tm dng y cung cp cho nhng c gi ,nhng ngi khng c tip xc vi cc kim t thp Gauss mt cch ngn gn gii thiu ni dung ny. Ni ngn gn kim t thp gauss c th c hiu nh nh l mt tp hp cc hnh nh vi phn gii khc nhau lin quan n mt hnh nh ban u theo mt cch nht nh. Nhng hnh nh ban u c phn gii cao nht c coi l mc thp nht, i khi gi l cp thp nht trong b ny. T cp thp nht ln cp cao nht phn gii gim n iu. C th, gia hai cp lin tip, mc trn l bng mt na nh l ln thp hn so vi c hai chiu ngang v dc. Mc trn c to ra bng cch p dng mt b lc thng thp cho mc thp, di y l mt mu ph 2x2. l, mi im nh mc trn l trng s trung bnh ca mt s im nh trong mc thp. Nhn chung, th tc c lp i lp li to ra mt mc trong cc thit lp tng ng vi mt trng s c th vi hnh nh ban u cp di tip theo l mt mu ph. Di iu kin nht nh, cc trng s chc nng gn st vi hm mt xc sut Gauss, l l do ti sao kim t thp c t tn theo gauss.Mt cu trc kim t thp guass c m t trong hnh 1.11. Lu rng cc kim t thp gauss m t trong hnh 1.11 nh l mt cu trc cy n gin ng vi mi node c 4 node mi. Trong cu trc kim t thp cy n gin, mi im nh trong mt cp trn u c gn mt gi tr tng ng vi 4 im nh trong mc thp hn.Ngay by gi ta tr li cuc tho lun v k thut a phn gii t trn xung di. Sau khi mt kim t thp gauss c xy dng, phm vi tm kim chuyn ng c phn b gia cc cu trc kim t thp l khc nhau. nh x khi c bt u cp phn gii thp nht c c mt c lng ban u ca vector chuyn ng.

Hnh 1. 11 Cu trc kim t thp gauss.1.3.7 Ngng a phn gii nh x khiVic hon thnh tnh ton vector chuyn ng ti mc phn gii thp c th khng ng v phi tip tc lc, trong khi nhng tnh ton khc c th tng i chnh xc v c th cung cp nn chuyn ng ca khi tng ng. Nhng quan st trn thc y mt phng thc nh x khi a phn gii mi vi k thut to ngng c pht trin .Cng vi k thut to ngng trc, c c lng vector chuyn ng cung cp nn chuyn ng, t tin trnh tip theo, do vy tit kim nhiu tnh ton. Phn tip theo, k thut ny trnh by chi tit cung cp cho c gi ci nhn su sc c hai k thut nh x khi a phn gii v nh x khi a phn gii to ngng.THUT TON Cho fn(x, y) l khung ca nh lin tc ti thi im n.

u tin, hai kim t thp Gausian c thit lp, kim t thp n v n-1, t 2 khung nh fn(x, y) v fn-1(x, y) tng ng. Cho php mc kim t thp biu thchy t = 1,.L, ti =1 l mc phn cao nht (top-level), L l phn gii thp nht (bottom- level), v +1 l tng s lp kim t thp. Nu (i,j) l ta gc bn tri ca mt khi ti mc ca kim t thp n, khi tham chiu nh l khi (i,j)1n. Cc kch thc theo chiu ngang v chiu dc ca mt khi ti mc biu th bi b1x v b1y tng ng.Kch thc khi trong bi ton ny thay i vi mc ca kim t thp.

Nu kch thc ca mt khi block ti level l b1x ,sau kch thc khi ti level (+1) tr thnh 2.b1x x 2.b1y. Phng thc thay i kch thc khi c s dng bi v n cho nhiu hiu qu nh gi chuyn ng hn phng thc c nh kch thc khi.

Tiu chun nh x c s dng cho nh gi chuyn ng l MAD bi v n khng yu cu nhn ln v biu din tng t nh MSE. MAD gia khi (i,j)1b1n ca khung hin ti v khi (i + vx, j + vy)1bln-1 ca khung trc ti mc c th tnh ton nh (1.7)

V = (v1x, v1y) l mt trong cc gi tr ca khi vector chuyn ng (i, j)1n, vl x, vly l hai thnh phn ca vector chuyn ng dc theo trc x v y, tng ng. Hnh 1.12 Kim t thp Gaussian c hnh thnh t hai khung hnh lin tip ca mt chui nh t c lng c chuyn ng mong mun. Sau nh x khi c thc hin cp cao nht vi biu tm kim ton b. c lng vector chuyn ng c kim tra nu chng c cung cp y nn chuyn ng. Nu yu cu chnh xc c p ng, sau vector chuyn ng s c truyn n mc phn gii cao hn tip theo bt u lc.Thut ton tip tc theo cch ny cho ti khi hai ngng c p ng hoc chm ti top-level. B qua mt s bc tnh ton mc trung gian cho tit kim tnh ton. Vic th nghim kh l phc tp chuyn ng khc nhau chng minh rng cc thut ton d kin gim thi gian x l t 14 n 20%, trong khi duy tr hu nh l cht lng ging nhau trong vic xy dng li hnh nh so vi thut ton nh x khi a phn gii hin l nhanh nht.

Hnh 1. 12 S khi ca nh x khi a phn gii ngng ba mc

Xc nh ngng Tiu chun mc chnh xc MAD c s dng trong phn ny nhm mc ich tit kim tnh ton. Gi tr ngng c mt s tc ng ti hiu nng ca thut ton a ra. Mt gi tr ngng nh c th ci thin cht lng xy dng li nh nhng chi ph ca tnh ton tng ln . Mt khc, gi tr ngng ln c th gim phc tp tnh ton, nhng cht lng xy dng li nh c th gim. Mt cch c th xc nh c mt gi tr ngng, iu ny c s dng trong rt nhiu th nghim bi Shi v Xia (1997), nh sau.T l nh tn hiu trn nhiu (PSNR) c dng ph bin nh l o cht lng ti to nh.

PSNR= 10log10 (1.8)T yu cu cho PSNR,ngi ta c th tm thy gi tr MSE cn thit. Mt cn bc hai ca gi tr MSE c th c chn la nh l mt gi tr ngng, gi tr ny c gn vo hai nh u tin t chui. Nu kt qu PSNR v thi gian ca qu trnh yu cu c tha mn,n sau c s dng cho phn cn li ca mt chui. Mt khc cc gi tr ngng c th c iu chnh cho ph hp v p dng vi nh th hai v th ba kim tra PSNR v thi gian x l. To ngng : c lng vector chuyn ng ti mi mc thp ca kim t s c kim tra nu chng cung cp s b chuyn ng l tha mn.

Gi s Vl (i,j)=(vlx,vly) l c lng vector chuyn ng cho khi (i,j)ln ti mc ca kim t thp n. Ngng Vl(i,j) c th th c a ra trc tip ti mc cui cng l mc 1.Vector chuyn ng nn cho cc khi mu ti mc di ca kim t thp n s l VL(2(L-1)i,2(L-1)j ) v c cho bi VL(2(L-1)i,2(L-l)j)=2(L-l)Vl(i,j) (1.9)Gi tr MAD gia cc khi ti mc cui cng ca kim t thp khung hin ti v n s c so snh trong khung trc c th xc nh c ty theo phng trnh 1.7. Vector chuyn ng l VL=VL.(2(L-l)i,2(L-l)j).Gi tr MAD c tnh ton c th c so snh vi ngng tham chiu.

Nu gi tr MAD l nh hn ngng, vector chuyn ng c tnh ton l VL(2(L-l)i,2(L-l)j) s c gn ti khi (2(L-l)i,2(L-l))Ln ti mc L trong khung hin ti v c tnh chuyn ng cho khi s dng li. Nu khng s c lng vector chuyn ng VL(i,j) ti mc s c lan truyn ti mc+1 . Hnh di y m t qu trnh x l ngng.

Hnh 1. 13 X l ngng1.4 Hn ch ca k thut nh x khiu tin, n c mt trng vect chuyn ng khng ng tin cy i vi chuyn ng thc trong khng gian 3-D. c bit, n khng tha mn d on chuyn ng v bn cnh n cn di chuyn dc theo ng bin.Th hai, n to ra cc khi o. Th ba, n cn phi x l thng tin ph. C ngha l, n cn phi m ho v truyn cc vector chuyn ng t u n cui ni nhn, do gy kh khn cho vic s dng cc khi c kch thc nh hn t c chnh xc cao trong d on chuyn ng.Tt c nhng hn ch l do m hnh n gin ca n: mi khi c gi nh l tnh tin u v cc vector chuyn ng ca khi c phn chia d on c lp nhau. Vic d on chuyn ng l khng tin cy, c bit l dc theo cc bin, gy ra d on nhiu li, do lm gim hiu qu m ha.Vi mt t l bit cao, mt s lng ln li d on b chuyn ng c th c chuyn n cui ni nhn, do ci thin c hiu qu th gic n mc nhng khi o khng lm kh chu cho ch th. T l bit c sn l thp, c bit l thp hn 64 kbps, nhng khi o tr nn kh chu vi th gic. Trong hnh 1.14, biu din li mt khung hnh "Miss America" bng cch hin th mt dy cc chui khung c t l bit thp. R rng, cc khi o lm ta thy rt kh chu nht l vng ming v cc vng tc c lin quan. Cc dy s c m ha v gii m s dng b m ha - gii m theo chun ITU-T trong khuyn ngh H.263, mt trong nhng tiu chun c s dng trong nh x khi d on chuyn ng.

Hnh 1.14 Dng li 21 chui khung ca "Miss America" s dng mt b m ha cho H.263.

1.5 Ci tin mi1.5.1 Cu trc phn cp nh x khiTrong phng php nghin cu kin trc phn tng cho cc block c kch thc khc nhau v s dng cc ca s tng quan. iu kin cn thit, xem xt kin trc phn tng vi 3 mc ca thut ton nh x khi. Khi nh x u tin l khi c kch thc ln nht trong cc khi v cc ca s tng quan. Bng cch s vector d on chuyn ng nh mt vector bt u ti mc th 2, ta li tm hiu vi block ln th 2 trong cc block v cc ca s tng quan. i vi mc th 3 ta cng lm tng t nh vy trn c s kt qu tm c ca mc th 2. Mt v d vi 3 c s tng quan c minh ha trong hnh 1.15. Cn ch rng vector chuyn ng tng l tng hp ca 3 vector chuyn ng thnh c xc nh trong 3 mc xem xt .Cc tham s trong 3 mc c lit k trong bng 1.3. Trc khi nh x, mt b lc thng thp c p dng cho ton b nh vic nh x tr nn tin cy. Cc b lc thng thp c s dng nh simply a local averaging. C ngha l, mc xm ca mi im nh c thay th bng gi tr trung bnh cc mc xm ca tt c cc im nh trong mt vng vung trung tm ti cc im nh m gi tr c gn. tnh ton gi tr ph hp vi tiu ch D, mt subsampling c p dng cho block ban u v ca s tng quan lu li php tnh.

Hnh 1. 15 Kin trc phn tng nh x khi

mc th nht, 8 im nh s c b tr u theo chiu ngang v chiu dc (a step size 8x8), nh x khi c thc hin vi dch chuyn ti a l 7 pixel, mt ca s tng quan c kch thc 64x64, v mt mu con c 4 x 4. Mt b lc thng thp c kch c trung bnh 5x5 c s dng trc khi thc hin first level block matching. mc th hai block matching c b tr u 4 im nh theo chiu ngang v chiu dc (a step size 8x8). Lu rng mt im nh ca vecto d on chuyn

Bng 1. 1 Cc thng s c s dng trong 3 mc ca kin trc phn tng nh x khiMc di chuyn ln nhtKch c ca s tng quanStep sizeKch thc b lc LPFCc mu con

17pel64x6485x54x4

23pel28x2845x54x4

33pel12x1225x52x2

Ngun: D liu t Bierling (1988)

Hnh 1. 16 Mt phn ca mt nh vi cc im nh c x l trong c 3 mc.ng s khng c xc nh trong mc u tin ca block matching, mc trung bnh ca bn im nh d on gn nht s c dng d on. Tt c cc tham s ca mc 2 c lit k trong bng 1.2. Mt iu cn phi c ch l trong block matching ti mc ca ca s nghin cu nn c thay th bi cc vc t d on chuyn ng thu c mc u tin. Mc th 3 ca block matching c x l sao cho ta c 2 im nh phn b u theo chiu ngang v chiu dc (a step size of 2x2). Cc thng s khc nhau c lit k trong bng 1.2Vic th nghim chng minh c tin cy ca d on chuyn ng do vy vic s dng cc kch thc khc nhau cho c cc khi ban u v ca s tng quan cng c p dng. Mc u tin vi mt kch thc ca s ln cng mt lot cc chuyn ng ln s xc nh c thnh phn chnh ng tin cy ca vecto chuyn ng. Cc mc tip theo vi kch thc ca s nh v chuyn di nh hn c kh nng ph hp vi cc vecto d on chuyn ng nhiu vng cc b.Hnh 1.16 cho thy mt phn ca mt nh vi cc im nh c x l trong c 3 mc tng ng. Lu rng n c th p dng thm mt hay nhiu phng php ni suy nh sau 3 mc trng vecto chuyn ng c c phn gii tt nht. Nh vy mt trng vecto chuyn ng c phn gii tt nht rt c li trong cc ng dng nh ni suy b chuyn ng trong thuc tnh ca videophony (in thoi truyn hnh). Ti , duy tr mt tc bit thp mt s khung hnh c b qua trong lc truyn. Ti pha nhn cc khung b b qua cn phi c ni suy. Ni suy b chuyn ng c th to ra cc khung c cht lng tt hn cc khung thu c khi s dng ni suy trng s tuyn tnh.1.6.2 Li a trong nh x khi

Hnh 1. 17 Minh ha 3 mc ca cu trc phn tngMt vi thut ton da trn cu trc a li c pht trin da trn vic ci tin k thut nh x khi. Hai phng php nng cao cng c gii thiu di y.To ngng a li nh x khi c th hiu l m hnh chuyn ng khi n gin (gi nh rng chuyn ng u vi kch thc khi c nh) trong k thut nh x khi l nguyn nhn gy ra mt vi hn ch, Chan et al. (1990) xut thay i kch thc cc block trong k thut nh x khi. tng chnh l s dng chin lc chia r v kt hp (split-and-merge) vi cu trc a li phn on mt hnh nh thnh mt tp cc khi c kch thc thay i, mi khi chuyn ng u. Mt cu trc cy nh phn (cn c gi l bin-tree) c s dng ghi li mi quan h gia cc block c kch c khc nhau.C th, ban u mt khung nh c chia thnh mt tp hp cc khi vung bng cch ct hnh nh ln lt theo chiu ngang v chiu dc. Vi mi khi c tao ra, mt khi nh x c thc hin cng vi khung trc ca n. (Then the matching accuracy in terms of the sum squared error is compared with a preset threshold). Sau tng bnh phng cc li c so snh vi gi tr ngng nh sn. Nu n nh hn hoc bng ngng, block vn khng thay i trong ton b qu trnh v vector d on chuyn ng l cui cng. Ngc li, block s c chia thnh hai khi, v mt nh x mi c thc hin cho hai block . Qu trnh ny tip tc cho n khi vecto d on tho mn mt iu kin v chnh xc trc hoc cc khi t c kch thc nh nht c nh sn. Ti im ny, mt quy trnh kt hp c xut bi Chan et al. Nu cc block c th kt hp, ln cn khi di nt trung gian trong cy nh phn s c kim tra, tc l, khi c kt hp c th c ly gn ng vi y chnh xc bi mt khi trong khung dng li trc . Lu rng vic kt hp c th c ty chn ty thuc vo tng ng dng c th.S khi ca a li nh x khi c biu din trong hnh 1.17. Lu rng tng t v ngng multiresolution nh x khi c nhc ti trong phn 1.3.6. Quan st s ging nhau gia cu trc a li v cu trc multiresolution: c hai u phn cp trong t nhin v c th d dng phn chia v kt hp. Mt v d v phn tch hnh nh v cy nh phn tng ng ca n c th hin hnh 1.18.Chan et al. (1990) cho rng, vi mt hnh nh ca mt con chut my tnh v mt ng xu, vic thay i kch thc block matching ln n 6dB ci thin SNR s gim khong 30% bit cn thit so vi kch thc block matching c nh (16x16). Mt s hi ngh truyn hnh in hnh, cc thut ton c xut lun thc hin tt hn so vi khi c kch thc c nh ca k thut nh x khi trong iu kin ci thin SNR dng li khung vi cng mt tc bt.

Hnh 1. 17 S thut ton a li nh x khi.Mt vi kt lun v k thut to ngng (thresholding). N cn thit cho vic m ho v truyn thng tin ph trn cy nh phn, n gii quyt s c ci t trc ngng, ni chung, cc thut ton c xut t c hiu sut tt hn so vi nh x khi kch thc c nh. Vi s linh hot thng qua cc phng php thay i kch thc, phng php ny l c kh nng lm cho cc m hnh ca chuyn ng u trong mi khi tr nn chnh xc hn so vi nh x kch thc c nh.Ti u a li nh x khi Mc tiu cui cng ca d on chuyn ng v b chuyn ng trong vic m ha video l cung cp mt m c hiu qu m ha cao trong thi gian thc. Theo cch khc, thc s th d on chuyn ng khng phi l mc tiu cui cng, mc d chnh xc ca d on chuyn ng l tha mn yu cu. Trc y yu cu i vi vecto d on chuyn ng l phi d on li nh nht v ng thi phi cha mt lng thng tin nht nh ca vecto chuyn ng, sau ny yu cu v chnh xc d on ca ng vect v phn gii cao trong trng vector chuyn ng.iu ny c Dufaux and Moscheni (1995) nhn mnh. H lm sng t cc c im ca m ha video, d on chuyn ng thc trong khng gian 3-D khng phi l mc tiu cui cng. Thay vo , vic d on chuyn ng s c th cung cp

Hnh 1. 18 To ngng a li nh x khi.d on thi gian tt v ng thi yu cu lng thng tin thp. In a word, tt c cc thng tin cn m ha nn gim n mc ti thiu. 1.6.3 nh x khi qua OVERLAPPER Tt c cc k thut c nhc n trong phn ny u nhm mc ch m bo tin cy cho d on chuyn ng. Kt qu l, h cng lm gim bt cc nhiu do khi o gy ra n mt mc nht nh. Trong phn ny, chng ta tho lun v mt nhm k thut, gi l overlapped block matching, pht trin lm gim bt hoc loi b cc khi o (Watanabe, 1991; Nogaki v Ohta, 1992; Auyeung et al., 1992). tng l lm gim nhng hn ch ca phn vng nonoverlapped block gy ra trong m hnh nh x khi c s. Sau khi nonoverlapped, c nh kch thc, phn nh vng khi hnh ch nht c thc hin, mi khi c m rng theo 4 pha t trung tm cc khi. Tham kho hnh 1.19. C d on chuyn ng (nh x khi) v d on b chuyn ng c tin hnh theo cch thc tng t nh nh x khi ngoi tr mt vi hm ca s.

Hnh 1. 19 Overlapped block matching.C ngha l, mt chc nng ca s 2-D c s dng duy tr mt mc nh lng thch hp dc theo phn chng cho. Phn r chc nng ca s theo hng ranh gii. (Nogaki v Ohta, 1992) mt chc nng ca s hnh sin c s dng.Tip theo, chng ti s dng cc thut ton c xut bi Nogaki v Ohta l mt v d minh ha c th loi k thut. Hy xem xt mt bn gc m rng, chng cho (cn c gi l mc tiu) khi, T(x,y), vi mt kch thc ca l x l. gi s l mt vector vI l mt trng lng r nc ng vinvin vector ang c xem xt. Phin bn d on ca khi mc tiu vi vi l biu hin bng vi, Pvi (x, y). Do , d on li vi vi, Evi (x, y) c th c tnh theo phng trnh sau y

(1.10) Chc nng ca s W (x, y) c p dng giai on ny nh sau, kt qu l mt ca s hot ng d bo li vi vi, Wevi.

(1.11)Gi nh rng MAD c s dng nh l ph hp vi tiu ch. N sau c th c xc nh nh bnh thng bng cch s dng ca s hot ng d bo li WEvi (x, y). l

(1.12)Ph hp nht, tng ng vi MAD ti thiu, sn xut thuyn vect v. D on chuyn ng bi thng, phin bn d on ca khi m rng mc tiu, Pv (x, y) c ngun gc t khung ti ti-1 bng cch s dng c tnh vc t v. Ca s cng chc nng W (x, y) c s dng to ra ca s-vn hnh d on Phin bn cui cng ca mc tiu khi. l

(1.9)Mt kch thc khi 16 x 16 c s dng cho khi thng thng ph hp, trong khi kch thc khi 32 x 32 c dng cho cc kt hp xut khi chng cho. Trng lng r nc ti a phm vi d c chp nh d = 15, tc l, t 15 + 15 trong c hai hng ngang v dc. M phng ng mt s gim trong sc mnh ca d on li bng khong 19%. Ch quan, n c quan st thy rng cnh chn ban u sn c trong d bo li tn hiu vi thng thng phn ln khi kt hp c g b vi chng cho khi xut kt hp k thut.2.Kt lun.Bi n nay, nh x khi c s dng thng xuyn hn bt k k thut c lng chuyn ng no khc trong m ha b chuyn ng. Bng phn chia mt khung thnh khong khng chng ph, cch u, c nh kch thc, khi hnh ch nht nh v gi nh rng tt c im nh trong mt khi cho trc ging nhau chuyn ng tnh tin, nh x khi trnh nhng kh khn gp trong c lng khi hnh dng ty chuyn ng. Do , nh x khi l n gin nht v ko theo gim i thng tin khc.Kch thc khi 16 x 16 l s dng thng xuyn. Trong nhiu c lng chuyn ng chnh xc, kch thc 8 x 8 cng thng c s dng.MAD u tin bi v tnh n gin trong thc nghim.Hn ch vi k thut nh x khi phn ln khng xc nh trng vector chuyn ng v khi o. Nguyn nhn bi m hnh n gin: mi khi o n bn chnh l c chuyn ng tnh tin. nh hng n ci thin mt hn ch. Vi k thut c s ci thin trn k thut nh x khi tho lun trong ny.Mc tiu cui cng ca nn chuyn ng trong m ha video l t c mc ich cao tnh hiu qu m ha. T quan im ny, trong nh x khi a li cp trc, gii quyt phn chia khi l thc hin khi bits s dng m ha thm vo motion vector lin quan n phn chia l t hn bits tit kim t m ha gim sai s d on do vy c lng chnh xc. Tiu chun thch nghi entropy l ngh v s dng ti u k thut nh x khi a li.

3.Ti liu tham kho[1] Block Matching Algorithms For Motion Estimation[2] Image and Video compression for Multimedia Engineering[3] Electrical and Computer Engineering Department University of Maryland, College Park Slide Min wu[4] EECS 274 Computer Vision of University California slide.D11VT3Page 8