MC LC

DANH MC CC K HIU, CM T VIT TT..3PHN M U......................................................................................................4 CHNG I. TNG QUAN V CH VIT V L THUYT NHN DNG........................................................................................................................5 1.1. GII THIU........................................................................................................6 1.2. M HNH TNG QUT CA MT H NHN DNG CH VIT TAY....6 1.2.1. Tin x l..........................................................................................................6 1.2.1.1. Nh phn ha nh...........................................................................................7 1.2.1.2. Lc nhiu........................................................................................................7 1.2.1.3. Chun ha kch thc nh.............................................................................7 1.2.1.4. Lm trn bin ch..........................................................................................8 1.2.1.5. Lm y ch...................................................................................................8 1.2.1.6. Lm mnh ch................................................................................................8 1.2.1.7. iu chnh nghing ca vn bn..............................................................8 1.2.2. Khi tch ch....................................................................................................9 1.2.2.1. Tch ch theo chiu nm ngang v thng ng............................................9 1.2.2.2. Tch ch dng lc sng..........................................................................9 1.2.3. Trch chn c trng.......................................................................................10 1.2.3.1. Bin i ton cc v khai trin chui..........................................................10 1.2.3.2. c trng thng k.......................................................................................11 1.2.3.3. c trng hnh hc v hnh thi..................................................................11 1.2.4. Hun luyn v nhn dng...............................................................................13 1.2.5. Hu x l........................................................................................................13 CHNG II. CC PHNG PHP NHN DNG CH VIT TAY..........................................................................................................................13 2.1. i snh mu.....................................................................................................13 2.2. Phng php tip cn cu trc..........................................................................142.2.1. Phng php ng php (Grammatical Methods):.........................................15 2.2.2. Phng php th (Graphical Methods):....................................................15 2.3. Mng n ron.......................................................................................................15 2.4. M hnh Markov n (HMM - Hidden Markov Model).......................................162.5. My vc t ta (SVM)........................................................................................16 2.5.1. Gii thiu..162.5.2. M hnh nhn dng ch vit tay ri rc172.5.2.1. Tin x l182.5.2.2. Trch chn c trng..182.5.2.3. La chn thut ton hun luyn phn lp.192.5.2.4. Thut ton nhn dng ch vit tay ri rc192.5.3. Kt qu thc nghim..202.5.3.1. Chun b cc b d liu thc nghim.212.5.3.2. Kt qu thc nghim trn b d liu MNIST212.5.3.3. Kt qu thc nghim trn d liu ch vit tay ting Vit..222.5.4. nh gi hiu qu phn lp SVM..222.5.5. Kt lun232.6. Kt hp cc k thut nhn dng.........................................................................24 2.6.1. Kin trc tun t.............................................................................................24 2.6.2. Kin trc song song........................................................................................25 2.6.3. Kin trc lai ghp...........................................................................................25 2.7. Kt lun..............................................................................................................25 CHNG III. NH GI,SO SNH CC PHNG PHP NHN DNG...26TI LIU THAM KHO.29

K hiu Thut ng

HMMMarkov Model (M hnh Markov n)

kernel hm nhn

KKT Karush-Kuhn-Tucker

k-NN k lng ging gn nht

Hm Lagrange ca bi ton gc (primal)

Hm Lagrange ca bi ton i ngu (dual)

Khng gian cc hm kh vi lin tc cp 2

MD Marginal Difference

MMD Maximum Marginal Difference

MNIST b mu ch s vit tay NIST - Vin Cng ngh v Tiu chun Quc gia Hoa K (National Institute of Standard and Technology of the United States)

NN Neuron Network (Mng n ron)

OCR Optical Character Recognition (nhn dng ch quang hc)

OVO One versus One

OVR One versus Rest

off-line ngoi tuyn

on-line trc tuyn

QP Quadratic Programing (quy hoch ton phng

RBF Radial Basic Function

SOM Self Origanizing Map

SMO Sequential Minimal Optimization

SV Support vector (vc t ta)

SVM Support Vector Machines (My vc t ta)

TSMN two-stage multinetwork (my phn lp a mng hai giai on)

USPS United States Postal service

VC Vapnik Chervonenkis

working set tp lm vic

||w||2 Chun Euclide ca siu phng

DANH MC CC K HIU, CM T VIT TT

PHN M U

Nhn dng ch l mt lnh vc c quan tm nghin cu v ng dng t nhiu nm nay theo hai hng chnh: Nhn dng ch in: phc v cho cng vic t ng ha c ti liu, tng tc v hiu qu nhp thng tin vo my tnh trc tip t cc ngun ti liu. Nhn dng ch vit tay: vi nhng mc rng buc khc nhau v cch vit, kiu ch... phc v cho cc ng dng c v x l chng t, ha n, phiu ghi, bn tho vit tay... Nhn dng ch vit tay c tch thnh hai hng pht trin: nhn dng ch vit tay trc tuyn (on-line) v nhn dng ch vit tay ngoi tuyn (off-line).

n thi im ny, bi ton nhn dng ch in c gii quyt gn nh trn vn (sn phm FineReader 9.0 ca hng ABBYY c th nhn dng ch in theo 20 ngn ng khc nhau, phn mm nhn dng ch Vit in VnDOCR 4.0 ca Vin Cng ngh Thng tin H Ni c th nhn dng c cc ti liu cha hnh nh, bng v vn bn ting Vit vi chnh xc trn 98%,...). Tuy nhin trn th gii cng nh Vit Nam, bi ton nhn dng ch vit tay vn cn l vn thch thc ln i vi cc nh nghin cu. Bi ton ny cha th gii quyt trn vn v n ph thuc qu nhiu vo ngi vit v s bin i qu a dng trong cch vit v trng thi tinh thn ca tng ngi vit. c bit i vi vic nghin cu nhn dng ch vit tay ting Vit li cng gp nhiu kh khn hn do b k t ting Vit c thm phn du, rt d nhm lm vi cc nhiu.

CHNG I. TNG QUAN V CH VIT V L THUYT NHN DNG1.1. GII THIU Nhn dng ch l lnh vc c nhiu nh nghin cu quan tm v cho n nay lnh vc ny cng t c nhiu thnh tu ln lao c v mt l thuyt ln ng dng thc t. Lnh vc nhn dng ch c chia lm hai loi: Nhn dng ch in v nhn dng ch vit tay. n thi im ny, nhn dng ch in c gii quyt gn nh trn vn. Tuy nhin, nhn dng ch vit tay vn ang l vn thch thc ln i vi cc nh nghin cu. Nhn dng ch vit tay c phn ra lm hai loi: nhn dng ch vit tay on-line (trc tuyn) v nhn dng ch vit tay off-line (ngoi tuyn). Nhn dng ch vit tay on-line c thc hin trn c s lu li cc thng tin v nt ch nh th t nt vit, hng v tc ca nt vit trong qu trnh n ang vit. y chnh l c s my tnh nhn din c cc ch ci, do vic nhn dng khng gp qu nhiu kh khn. Mt trong nhng sn phm nhn dng ch vit tay trc tuyn tiu biu nht l h thng nhn dng ch vit tay ri rc trc tuyn trn mt trm lm vic ca IBM do H.S.M.Beigi, C.C.Tapert, M.Ukeison v C.G.Wolf phng thc hnh Watson IBM ci t [6]. Ngc li, i vi nhn dng ch vit tay off-line, d liu u vo l nh vn bn c qut vo nn vic nhn dng c kh cao hn nhiu so vi nhn dng ch vit tay on-line. Do d liu u vo l nh vn bn nn nhn dng ch vit tay off-line v nhn dng ch in cn c gi chung l nhn dng ch quang hc (OCR - Optical Character Recognition). Kh khn ln nht khi nghin cu bi ton nhn dng ch vit tay l s bin thin qu a dng trong cch vit ca tng ngi. Cng mt ngi vit nhng i khi cng c nhiu s khc bit trong cch vit tu thuc vo tng ng cnh, kiu vit ca mt ngi cng c th thay i theo thi gian hoc theo thi quen... iu ny gy ra nhiu tr ngi trong vic trch chn c trng cng nh la chn m hnh nhn dng.1.2. M HNH TNG QUT CA MT H NHN DNG CH VIT TAY.1.2.1. Tin x l Giai on ny gp phn lm tng chnh xc phn lp ca h thng nhn dng, tuy nhin n cng lm cho tc nhn dng ca h thng chm li. V vy, ty thuc vo cht lng nh qut vo ca tng vn bn c th chn mt hoc mt vi chc nng trong khi ny. Nu cn u tin tc x l v cht lng ca my qut tt th c th b qua giai on ny. Khi tin x l bao gm mt s chc nng: Nh phn ha nh, lc nhiu, chun ha kch thc nh, lm trn bin ch, lm y ch, lm mnh ch v xoay vn bn.

1.2.1.1. Nh phn ha nh Nh phn ha nh l mt k thut chuyn nh a cp xm sang nh nh phn. Trong bt k bi ton phn tch hoc nng cao cht lng nh no, n cng cn thit xc nh cc i tng quan trng. Nh phn ha nh phn chia nh thnh 2 phn: phn nn v phn ch. Hu ht cc phng php nh phn ha nh hin nay u la chn mt ngng thch hp theo cng sng ca nh v sau chuyn tt c cc gi tr sng ln hn ngng thnh mt gi tr sng (v d trng) v tt c cc gi tr b hn ngng thnh mt gi tr sng khc (en). Hnh 1.2. Nh phn ha nh.1.2.1.2. Lc nhiu Nhiu l mt tp cc im sng tha trn nh. Kh nhiu l mt vn thng gp trong nhn dng, nhiu c nhiu loi (nhiu m, nhiu vt, nhiu t nt...).

Hnh 1.3. Nhiu m v nhiu vt. kh cc nhiu m (cc nhiu vi kch thc nh), c th s dng cc phng php lc (lc trung bnh, lc trung v...). Tuy nhin, vi cc nhiu vt (hoc cc nhiu c kch thc ln) th cc phng php lc t ra km hiu qu, trong trng hp ny s dng phng php kh cc vng lin thng nh t ra c hiu qu hn.1.2.1.3. Chun ha kch thc nh

Hnh 1.4. Chun ha kch thc nh cc k t A v P. Vic chun ha kch thc nh da trn vic xc nh trng tm nh, sau xc nh khong cch ln nht t tm nh n cc cnh trn, di, tri, phi ca hnh ch nht bao quanh nh. Thng qua khong cch ln nht , c th xc nh c mt t l co, gin ca nh gc so vi kch thc xc nh, t hiu chnh kch thc nh theo t l co, gin ny. Nh vy, thut ton chun ha kch thc nh lun lun m bo c tnh cn bng khi co gin nh, nh s khng b bin dng hoc b lch.1.2.1.4. Lm trn bin ch i khi do cht lng qut nh qu xu, cc ng bin ca ch khng cn gi c dng iu trn tru ban u m hnh thnh cc ng rng ca gi to. Trong cc trng hp ny, phi dng cc thut ton lm trn bin khc phc [28].

(a) (b) Hnh 1.5. (a) nh gc, (b) nh sau khi c lm trn bin.1.2.1.5. Lm y ch Chc nng ny c p dng vi cc k t b t nt mt cch ngu nhin. nh t nt gy kh khn cho vic tch ch, d b nhm hai phn lin thng ca k t thnh hai k t ring bit, to nn sai lm trong qu trnh nhn dng. 1.2.1.6. Lm mnh ch y l mt bc quan trng nhm pht hin khung xng ca k t bng cch loi b dn cc im bin ngoi ca cc nt. Tuy nhin, qu trnh lm mnh ch rt nhy cm vi vic kh nhiu. Hin nay c nhiu phng php lm mnh ch, cc thut ton tm xng c th tham kho [28].

Hnh 1.6. Lm mnh ch.1.2.1.7. iu chnh nghing ca vn bn Do trang ti liu qut vo khng cn thn hoc do s c in n, cc hng ch b lch so vi l chun mt gc , iu ny gy kh khn cho cng on tch ch, i khi khng th tch c. Trong nhng trng hp nh vy, phi tnh li ta im nh ca cc ch b sai lch. C nhiu k thut iu chnh nghing, k thut ph bin nht da trn c s biu chiu (projection profile) ca nh ti liu; mt s k thut da trn c s cc php bin i Hough v Fourier. mt s k thut hiu chnh nghing khc c th tm thy trong [28]. Hnh 1.7. Hiu chnh nghing ca vn bn.1.2.2. Khi tch ch Khi ny c nhim v tch tng k t ra khi vn bn. Ch khi no vn bn c tch v c lp ng tng k t n ra khi tng th vn bn th h thng mi c th nhn dng ng k t . Sau y l mt s phng php tch ch thng dng: 1.2.2.1. Tch ch theo chiu nm ngang v thng ng Phng php ny thng p dng cho ch in. Khc vi ch vit tay, kch thc v kiu ch c nh, phi tun theo mt s quy nh in n, cc ch phi nm gn trong mt khung nn vic c lp mt k t n c th ng nht vi vic tm ra khung bao ca ch ti v tr ca n trong vn bn. Tch ch theo chiu nm ngang v thng ng l tm mt hnh ch nht c cnh thng ng v nm ngang cha trn mt k t bn trong. 1.2.2.2. Tch ch dng lc sng

Hnh 1.8. Tch dng ch da trn histogram theo chiu ngang ca khi ch. i vi ch vit tay th vic tm ng phn cch gia cc dng v cc k t trong vn bn thng rt kh khn. Trong trng hp ny, khng th tm ng phn cch theo ngha thng thng m phi hiu l ng phn cch vi s im ct hai dng l t nht. Khi phi xy dng lc sng ca cc dng ch, t cc on thp nht trn lc chnh l ng phn cch cn tm (hnh 1.8 v 1.9).

Hnh 1.9. Xc nh khong cch gia hai k t v gia hai t da trn histogram theo chiu thng ng ca dng ch.1.2.3. Trch chn c trng Trch chn c trng ng vai tr cc k quan trng trong mt h thng nhn dng. Trong trng hp n gin nht, nh a cp xm hoc nh nh phn c s dng cho vic nhn dng. Tuy nhin, trong hu ht cc h nhn dng, gim phc tp v tng chnh xc ca cc thut ton phn lp th i hi cc c trng c trch chn phi rt gn li cng nh cng tt nhng vn phi m bo c thng tin ca k t. Vi mc tiu ny, mt tp cc c trng c trch chn cho mi lp sao cho c th phn bit c vi cc lp khc. Mt s phng php trch chn c trng tng i tt i vi nhn dng ch vit tay c th tham kho trong [27,28]. C hng trm phng php trch chn c trng cho nh vn bn, nhng chung quy li, cc phng php ny c gom li thnh ba nhm chnh sau:1.2.3.1. Bin i ton cc v khai trin chui Mt tn hiu lin tc thng cha nhiu thng tin v chng c th s dng lm cc c trng cho mc ch phn lp. Cc c trng c trch chn cng c th ng i vi vic xp x cc tn hiu lin tc thnh cc tn hiu ri rc. Mt cch biu din mt tn hiu l s dng mt t hp tuyn tnh ca mt dy cc hm n gin hn. Cc h s ca t hp tuyn tnh cung cp mt tri thc gii m va , chng hn nh cc php bin i hoc khai trin chui. Mt s bin dng khc nh cc php dch chuyn v php quay l bt bin di cc php bin i ton cc v khai trin chui. Sau y l mt s phng php bin i v khai trin chui thng c p dng trong lnh vc nhn dng ch: Bin i Fourier: Mt trong nhng tnh cht ni bt nht ca php bin i Fourier l kh nng nhn dng cc k t c s thay i v cc t th khc nhau, cc php bin i ny c p dng nhn dng k t theo nhiu cch khc nhau [29,30]. Bin i Wavelet: Php bin i ny l mt dy cc k thut khai trin cho php m t c trng ca nh cc mc khc nhau. Cc cng on tch ch thnh cc k t hoc t c m t bng cc h s wavelet theo cc mc khc nhau i vi tng gii php. Sau cc h s wavelet c chuyn qua mt my phn lp phc v cho vic nhn dng [31,32]. Phng php m men: Theo phng php ny, nh gc s c thay th bng mt tp cc c trng va ca nhn dng cc i tng bt bin i vi cc php thay i t l, tnh tin hoc quay [33]. Cc m men c xt nh cc dy khai trin c trng v nh gc c th xy dng li mt cch y t cc h s m men. Khai trin Karhunent-Loeve: Vic khai trin ny nhm phn tch cc vc t ring rt gn s chiu ca tp c trng bng cch to ra cc c trng mi l t hp tuyn tnh ca cc c trng gc. y ch l mt php bin i ti u trong mt s gii hn no ca vic nn thng tin [34]. Khai trin Karhunent-Loeve c dng trong mt s bi ton nhn dng mu nh nhn dng mt ngi, n cng c s dng trong h thng OCR ca Vin Cng ngh v Tiu chun Quc gia Hoa K (NIST National Institute of Standards and Technology of the United States). V vic khai trin ny i hi phi s dng cc thut ton c khi lng tnh ton rt ln nn vic s dng cc c trng Karhunent-Loeve trong cc bi ton nhn dng ch khng c ph bin rng ri. Tuy nhin, tng tc tnh ton cho cc my phn lp, cc c trng ny tr nn thit thc hn cho cc h nhn dng ch trong nhng nm gn y. 1.2.3.2. c trng thng k Cc c trng thng k ca nh vn bn bo ton cc kiu bin i a dng v hnh dng ca ch. Mc d cc kiu c trng ny khng th xy dng li nh gc, nhng n c s dng thu nh s chiu ca tp c trng nhm tng tc v gim thiu phc tp tnh ton. Sau y l mt s c trng thng k thng dng biu din nh k t: Phn vng (zoning): Khung cha k t c chia thnh mt vi vng chng nhau hoc khng chng nhau. Mc ca cc im nh trong cc vng khc nhau c phn tch v to thnh cc c trng [22,23,24]. Cc giao im v khong cch: Mt c trng thng k ph bin l s giao im gia chu tuyn ca ch vi mt ng thng theo mt hng c bit no . Trong [35], khung cha k t c phn chia thnh mt tp cc vng theo cc hng khc nhau v sau cc dy en trong mi vng c m ha bi cc s ly tha ca 2. Tng t nh vy, khong cch t bin ca khung cha nh ti im en u tin ca chu tuyn ch trn cng mt dng qut cng c s dng nh nhng c trng thng k [24]. Cc php chiu: Cc k t c th c biu din bng cch chiu cc gi tr mc xm ca tng im ln trn cc dng theo cc hng khc nhau. Cc c trng ny to ra dy tn hiu mt chiu t nh hai chiu [22,23,24]. c trng hng: Cc k t bao gm cc nt ch, cc nt ny l cc on thng c hng, cc cung hoc cc ng cong. Hng ca cc nt ng vai tr quan trng trong vic so snh s khc nhau gia cc k t. Cc k t c m t nh cc vc t m cc phn t ca n l cc gi tr thng k v hng. trch chn cc c trng ny, gc nh hng ca nt ch phi c phn chia thnh mt s vng c nh v s cc on ca nt ch trong mi vng gc c chn nh mt gi tr c trng. V vy, tp cc s lng ca cc on nh hng s to thnh mt biu c gi l biu hng v cc c trng v biu hng c th gi chung l c trng hng. Cc nh k t c phn r thnh cc mt phng nh hng v mt o khong cch c tnh gia cc mt phng vi mu ca mi lp. Hng nt ch cc b ca mt k t c th c xc nh bng nhiu cch khc nhau: hng ca xng, phn on nt ch, m ha chu tuyn, hng o hm [28]. Hin nay, cc c trng m ha chu tuyn v hng o hm c p dng rng ri v chng d ci t v xp x bt bin vi s bin i a dng ca cc nt ch. 1.2.3.3. c trng hnh hc v hnh thi Cc tnh cht cc b v ton cc khc nhau ca cc k t c th c biu din bng cc c trng hnh hc v hnh thi. Cc kiu c trng ny cng c th gii m mt s tri thc v cu trc ca i tng nh hoc c th cung cp mt s tri thc nh sp xp cc thnh phn to ra i tng. Cc loi c trng ny c th phn thnh cc nhm sau: Trch chn v m cc cu trc hnh thi: trong nhm c trng ny, mt cu trc xc nh c tm kim trong mt k t hoc mt t. S lng v tr hoc quan h v tr ca cc cu trc trong k t ny to thnh cc c trng biu din k t. Thng thng, cc cu trc nguyn thy (cc on thng, cc cung) l cc nt to ra k t. Cc k t v cc t c th c m t bng cch trch chn v m nhiu loi c trng v hnh thi nh cc im cc i v cc tiu, cc im chp trn v chop di ca mt ngng no , m rng cho cc im tri, phi, trn, di v cc giao im, cc im nhnh, im cui on thng, hng ca mt nt t mt im c bit, cc im c lp... to nn cc k t [36,37]. o v xp x cc tnh cht hnh hc: trong nhiu cng trnh nghin cu [38,39], cc k t c biu din bng o ca cc i lng hnh hc nh t s gia chiu rng v chiu cao ca hp cha k t, quan h khong cch gia hai im, so snh di gia hai nt, rng ca mt nt, khi lng ch hoa v ch thng ca cc t, di t. Mt o tiu biu rt quan trng na l cong hoc thay i cong [40]. Cc i lng hnh hc o c c th xp x bi mt tp cc c trng hnh hc va v thun tin hn [41]. th v cy: u tin, cc t hoc cc k t c phn chia thnh mt tp cc i tng nguyn thy nh cc nt, cc im chc... Sau , cc thnh phn nguyn thy c thay th bng cc thuc tnh hoc cc th lin quan [42]. C hai loi c trng nh c m t bng th. Loi th nht s dng cc ta ca hnh dng k t [43]. Loi th hai l mt c trng tru tng, cc nt ca th tng ng vi cc nt ch v cc cnh ca th tng ng vi cc mi quan h gia cc nt ch [44]. Cy cng c th dng biu din cc t v cc k t vi mt tp cc c trng theo mt quan h phn cp [45]. Trch chn c trng hu ht c thc hin trn nh nh phn. Tuy nhin, vic nh phn ha nh a cp xm c th xa i mt s thng tin quan trng ca cc k t. Trong trng hp ny, cng c mt s cng trnh nghin cu trch chn cc c trng trc tip t cc nh a cp xm [46]. Cui cng, mc ch chnh ca vic trch chn c trng l la chn mt tp c trng phc v cho vic phn lp sao cho h thng nhn dng t chnh xc cao nht vi s lng phn t c trch chn t nht. Lun n ch tp trung nghin cu mt s c trng thng k v c trng wavelet cho bi ton nhn dng ch Vit vit tay ri rc. 1.2.4. Hun luyn v nhn dng y l giai on quan trng nht, giai on ny quyt nh chnh xc ca h thng nhn dng. C nhiu phng php phn lp khc nhau c p dng cho cc h thng nhn dng ch vit tay. Cc phng php ny s c phn tch c th trong phn 1.3. 1.2.5. Hu x l y l cng on cui cng ca qu trnh nhn dng. C th hiu hu x l l bc ghp ni cc k t nhn dng thnh cc t, cc cu, cc on vn nhm ti hin li vn bn ng thi pht hin ra cc li nhn dng sai bng cch kim tra chnh t da trn cu trc v ng ngha ca cc t, cc cu hoc cc on vn. Vic pht hin ra cc li, cc sai st trong nhn dng bc ny gp phn ng k vo vic nng cao cht lng nhn dng. Cch n gin nht kt ni cc thng tin ng cnh l tn dng mt t in iu chnh cc li ca h thng nhn dng. tng c bn ny da trn c s nh vn kim tra u ra ca h thng nhn dng v cung cp mt s kh nng cho cc u ra ca my nhn dng khi cc u ra ny khng nm ng v tr trong t in [47]. Vic kim tra li chnh t ph hp vi mt s ngn ng nh Anh, Php, c, Vit Nam,... M hnh ngn ng thng k N-Grams c p dng kh thnh cng trong vic kim tra chnh t cng on hu x l ca cc h thng nhn dng ch vit v cc h thng nhn dng ting ni [48,49]. Trong m hnh N-Grams, mi t ch ph thuc vo n t ng trc, gi thit ny rt quan trng trong vic hun luyn m hnh v n lm gim ng k phc tp ca bi ton hc m hnh ngn ng t tp d liu hun luyn.II. CC PHNG PHP NHN DNG CH VIT TAY C nhiu phng php nhn dng mu khc nhau c p dng rng ri trong cc h thng nhn dng ch vit tay. Cc phng php ny c th c tch hp trong cc hng tip cn sau: i snh mu, thng k, cu trc, mng n ron v SVM.2.1 i snh mu K thut nhn dng ch n gin nht da trn c s i snh cc nguyn mu (prototype) vi nhau nhn dng k t hoc t. Ni chung, ton t i snh xc nh mc ging nhau gia hai v t (nhm cc im, hnh dng, cong...) trong mt khng gian c trng. Cc k thut i snh c th nghin cu theo ba hng sau: i snh trc tip: Mt k t u vo l nh a cp xm hoc nh nh phn c so snh trc tip vi mt tp mu chun c lu tr. Vic so snh da theo mt o v s tng ng no (chng hn nh o Euclide) nhn dng. Cc k thut i snh ny c th n gin nh vic so snh mt mt hoc phc tp hn nh phn tch cy quyt nh [50,51]. Mc d phng php i snh trc tip n gin v c mt c s ton hc vng chc nhng kt qu nhn dng ca n cng rt nhy cm vi nhiu. Cc mu bin dng v i snh mm: Mt phng php i snh khc l s dng cc mu bin dng, trong mt php bin dng nh c dng i snh mt nh cha bit vi mt c s d liu nh bit [52]. tng c bn ca i snh mm l i snh mt cch ti u mu cha bit vi tt c cc mu c th m cc mu ny c th ko gin ra hoc co li. Ch mt khng gian c trng c thnh lp, cc vc t cha bit c i snh bng cch s dng quy hoch ng v mt hm bin dng [53,54]. i snh gim nh: y l mt k thut i snh nh mc tng trng, k thut ny s dng hnh dng c trng c bn ca nh k t. Th nht, cc vng i snh c nhn bit. Sau , trn c s mt s vng i snh c nh gi tt, cc phn t ca nh c so snh vi cc vng i snh ny. Cng vic ny i hi mt k thut tm kim trong mt khng gian a chiu tm cc i ton cc ca mt s hm [55]. Cc k thut i snh mu ch p dng tt i vi nhn dng ch in, cn i vi ch vit tay th cc k thut ny t ra km hiu qu.2.2. Phng php tip cn cu trc Cch tip cn ca phng php ny da vo vic m t i tng nh mt s khi nim biu din i tng c s trong ngn ng t nhin. m t i tng ngi ta dng mt s dng nguyn thu nh on thng, cung, Mi i tng c m t nh mt s kt hp ca cc dng nguyn thu. Cc quy tc kt hp cc dng nguyn thu c xy dng ging nh vic nghin cu vn phm trong mt ngn ng, do qu trnh quyt nh nhn dng l qu trnh phn tch c php [57,58]. Phng php ny t vn gii quyt bi ton nhn dng ch tng qut. Tuy vy, cho n nay cn nhiu vn lin quan n h nhn dng c php cha c gii quyt c lp v cha xy dng c cc thut ton ph dng. Hin nay, nhn dng theo cu trc ph bin l trch trn cc c trng ca mu hc, phn hoch bng k t da trn cc c trng ny, sau nh cn nhn dng s c trch chn c trng, sau so snh trn bng phn hoch tm ra k t c cc c trng ph hp. i vi nhn dng ch vit tay ri rc da theo cu trc xng v ng bin, cng vic ny i hi phi xy dng cc c trng ca ch, c bit l c trng v cc im un, im gp khc v c trng ca cc nt. Sau khi tin hnh cng on tin x l, cng vic tch cc nt c tin hnh thng qua cc im chc. Sau trch chn c trng cu trc xng ca ch, mi nt c trng bi cp ch s u v cui tng ng vi th t ca im chc u v im chc cui. Cui cng l xy dng cy tm kim, da vo c trng v cu trc xng v cu trc bin phn tp mu hc thnh cc lp. Qu trnh tm kim phn lp c tin hnh qua hai bc: Xc nh lp tng ng vi mu vo v tm kim trong lp mu no gn ging vi mu vo nht [62,63]. Cc phng php cu trc p dng cho cc bi ton nhn dng ch c pht trin theo hai hng sau:2.2.1. Phng php ng php (Grammatical Methods): Gia thp nin 1960, cc nh nghin cu bt u xt cc lut ca ngn ng hc phn tch ting ni v ch vit. Sau , cc lut a dng ca chnh t, t vng v ngn ng hc c p dng cho cc chin lc nhn dng. Cc phng php ng php khi to mt s lut sinh hnh thnh cc k t t mt tp cc cng thc ng php nguyn thy. Cc lut sinh ny c th kt ni bt k kiu c trng thng k v c trng hnh thi no di mt s c php hoc cc lut ng ngha [56,57,58]. Ging nh l thuyt ngn ng, cc lut sinh cho php m t cc cu trc cu c th chp nhn c v trch chn thng tin theo ng cnh v ch vit bng cch s dng cc kiu ng php khc nhau [59].Trong cc phng php ny, vic hun luyn c thc hin bng cch m t mi k t bng mt vn phm Gi. Cn trong pha nhn dng th chui, cy hoc th ca mt n v vit bt k (k t, t hoc cu) c phn tch quyt nh vn phm ca mu thuc lp no. Cc phng php ng php hu ht c s dng trong giai on hu x l sa cc li m khi nhn dng thc hin sai [60,61]. 2.2.2. Phng php th (Graphical Methods): Cc n v ch vit c m t bi cc cy hoc cc th. Cc dng nguyn thy ca k t (cc nt) c la chn bi mt hng tip cn cu trc. i vi mi lp, mt th hoc cy c thnh lp trong giai on hun luyn m t cc nt, cc k t hoc cc t. Giai on nhn dng gn mt th cha bit vo mt trong cc lp bng cch s dng mt o so snh cc c im ging nhau gia cc th. C rt nhiu hng tip cn khc nhau s dng phng php th, tiu biu l hng tip cn th phn cp c dng trong vic nhn dng ch vit tay Trung Quc v Hn Quc [62,63]. 2.3. Mng n ron Mt mng n ron c nh ngha nh mt cu trc tnh ton bao gm nhiu b x l n ron c kt ni song song chng cht vi nhau. Do bn cht song song ca cc n ron nn n c th thc hin cc tnh ton vi tc cao hn so vi cc k thut phn lp khc. Mt mng n ron cha nhiu nt, u ra ca mt nt c s dng cho mt nt khc trong mng v hm quyt nh cui cng ph thuc vo s tng tc phc tp gia cc nt. Mc d nguyn l khc nhau, nhng hu ht cc kin trc mng n ron u tng ng vi cc phng php nhn dng mu thng k [26,27]. Cc kin trc mng n ron c th c phn thnh hai nhm chnh: mng truyn thng v mng lan truyn ngc. Trong cc h thng nhn dng ch, cc mng n ron s dng ph bin nht l mng perceptron a lp thuc nhm mng truyn thng v mng SOM (Self Origanizing Map) ca Kohonen thuc nhm mng lan truyn ngc. Mng perceptron a lp c xut bi Rosenblatt [64] c nhiu tc gi s dng trong cc h nhn dng ch vit tay [65,66]. Hu ht cc nghin cu pht trin nhn dng ch vit tay hin nay u tp trung vo mng SOM [67]. SOM kt hp trch chn c trng v nhn dng trn mt tp ln cc k t hun luyn. Mng ny chng t rng n tng ng vi thut ton phn cm k-means. Vi thut ton n gin nhng rt hiu qu, cng vi thnh cng ca m hnh ny trong cc ng dng thc tin, mng n ron hin ang l mt trong cc hng nghin cu ca lnh vc hc my. Mng n ron t ra ph hp vi cc bi ton i snh, phn loi mu, xp x hm, ti u ho, lng t ho vc t v phn hoch khng gian d liu, trong khi cc phng php truyn thng khng kh nng gii quyt cc vn nu trn mt cch hiu qu. c bit trong cc h thng nhn dng s dng mng n ron t c t l nhn dng kh chnh xc, c th so snh vi cc phng php nhn dng cu trc, thng k, 2.4. M hnh Markov n (HMM - Hidden Markov Model) HMM l mt m hnh xc sut hu hn trng thi theo kiu pht sinh tin trnh bng cch nh ngha xc sut lin kt trn cc chui quan st. Mi chui quan st c sinh ra bi mt chui cc php chuyn trng thi, bt u t trng thi khi u cho n khi thu c trng thi kt thc. Ti mi trng thi th mt phn t ca chui quan st c pht sinh ngu nhin trc khi chuyn sang trng thi tip theo. Cc trng thi ca HMM c xem l n bn trong m hnh v ti mi thi im ch nhn thy cc k hiu quan st cn cc trng thi cng nh s chuyn i trng thi c vn hnh n bn trong m hnh [70]. HMM tng c p dng rng ri i vi cc bi ton nhn dng ch vit tay mc t [71,72,73,74,75]. 2.5. My vc t ta (SVM) 2.5.1. Gii thiu Cho n nay, vic nhn dng ch vit tay vn cha c c mt gii php tng th, cc ng dng ca n cng ch gii hn trong phm vi hp. Cc kt qu ch yu v lnh vc ny ch tp trung trn cc tp d liu ch s vit tay chun nh USPS v MNIST [5.3,5.1,87], bn cnh cng c mt s cng trnh nghin cu trn cc h ch ci ting La tinh, Hy Lp, Trung Quc, Vit Nam... tuy nhin cc kt qu t c cng cn nhiu hn ch [88,89,5.2,5.4]. Cc gii php tip cn gii bi ton nhn dng ch vit tay kh phong ph, mt s phng php hc my thng c p dng nh: m hnh Markov n, mng n ron hay phng php my vc t ta (SVM - Support Vector Machines). Trong SVM c nh gi l phng php hc my tin tin ang c p dng rng ri trong cc lnh khai ph d liu v th gic my tnh SVM gc c thit k gii bi ton phn lp nh phn, tng chnh ca phng php ny l tm mt siu phng phn cch sao cho khong cch l gia hai lp t cc i. Khong cch ny c xc nh bi cc vc t ta (SV - Support Vector), cc SV ny c lc ra t tp mu hun luyn bng cch gii mt bi ton ti u li [5.1]. Trong bi bo ny, chng ti s xy dng m hnh nhn dng ch vit tay ri rc da trn phng php SVM, ng thi tin hnh ci t th nghim trn cc tp d liu ch s vit tay chun MNIST v d liu ch vit tay ting Vit do chng ti t thu thp.2.5.2. M hnh nhn dng ch vit tay ri rc. Trong phn ny, chng ti s tp trung xy dng m hnh nhn dng ch vit tay ri rc theo phng php phn lp SVM. Cng vic c thc hin theo hai bc chnh sau y:Bc 1: Xy dng m hnh hun luyn. Tp d liu hun luyn sau khi qua cc khu tin x l v trch chn c trng s c a vo my hun luyn phn lp SVM. Sau khi kt thc qu trnh hun luyn, h thng s lu li gi tr cc tham s ca hm quyt nh phn lp phc v cho vic nhn dng sau ny. Qu trnh hun luyn tiu tn kh nhiu thi gian, tc hun luyn nhanh hay chm ty thuc vo tng thut ton hun luyn, chin lc phn lp SVM cng nh s lng mu tham gia hun luyn.Bc 2: Phn lp nhn dng. Da vo gi tr cc tham s ca hm quyt nh thu c Bc 1, mt mu mi x sau khi qua cc khu tin x l v trch chn c trng s c a vo tnh ton thng qua hm quyt nh xc nh lp ca mu x (Hnh 2.1).

Hnh 2.1. M hnh nhn dng ch vit tay ri rc.2.5.2.1. Tin x l.Sau khi kh nhiu, nh c chun ha v kch thc chun 1616. Vic chun ha kch thc nh c thc hin theo cc bc sau:Bc 1: Nh phn ha nh.Bc 2: Tm hnh ch nht R b nht cha cc im en trn nh.Bc 3: Ly vng nh I nm trong hnh ch nht R.Bc 4: Chun ha nh I v kch thc chun 1616.2.5.2.2. Trch chn c trngTrong phn ny, chng ti s chn phng php trch chn c trng n gin nhng hiu qu, c th p dng cho cc tp d liu ch vit tay ri rc. nh k t sau khi chun ha v kch thc chun s c chia thnh NN vng (Hnh 2.2). Tng s im en ca mi vng s c chn to thnh cc vect c trng.

Hnh 2.2. Trch chn c trng trng s vng.Trong thc nghim, vi nh kch thc 1616, chn N=8, nh vy c 88 = 64 c trng.2.5.2.3. La chn thut ton hun luyn phn lpTrong phn ci t thc nghim, chng ti p dng thut ton SMO hun luyn phn lp SVM nh phn, s dng v k tha mt s chc nng ca phn mm m ngun m LibSVM [86] pht trin ng dng nhn dng ch vit tay ri rc.2.5.2.4. Thut ton nhn dng ch vit tay ri rc.C hai chin lc phn lp OVO v OVR u c th p dng phn lp d liu mt cch tng qut m khng cn phi can thip su phn tch cc c trng khc nhau gia cc lp d liu [5.3]. V vy hai chin lc phn lp ny s c chng ti la chn ci t th nghim thut ton nhn dng i vi d liu ch vit tay ri rc.Procedure SVMClassify//Thut ton phn lp theo 2 chin lc OVO v OVRInput: - Mu x;- S lp N;- Chin lc phn lp Strategy;- Cc m hnh hun luyn {OVOModel, OVRModel}Output: label; // Nhn lp ca mu xMethod1. Case Strategy of2. OVO:// Chin lc mt i mt3. Khi to Count[i] = 0; // i=0,..,N-14. LoadModel(OVOModel);5. for (i=0; i < N-1; i++)6. for (j=i+1; j < N; j++) 7. Count[BinarySVM(x,i,j)]++;8. Count[label]=Max(Count[i]);9. OVR: // Chin lc mt i phn cn li10. LoadModel(OVRModel);11. label=-1; 12. for (i=0; i < N; i++) 13.{ 14. label=BinarySVM(x,i,Rest);15. if(label=i) break;16. }17. EndCase;18. Return label;Trong :BinarySVM(x,i,j) l hm xp x vo mt trong hai lp i hoc j,Count[ ] l mng bin m lu s ln nhn din ca cc lp. 2.5.3. Kt qu thc nghim.Cc kt qu thc nghim c ci t v chy th nghim trn mi trng Window XP, my PC Pentium 4 tc 2.4 Ghz vi dung lng b nh RAM 1Gb.2.5.3.1. Chun b cc b d liu thc nghim.B d liu chun MNISTB d liu MNIST bao gm 60.000 mu hun luyn v 10.000 mu khc nhn dng, mi mu l mt nh kch thc 2828. B d liu ch vit tay ting VitChng ti xy dng b d liu ch vit tay ting Vit (VietData) phc v cho vic thc nghim bao gm 89 lp ch ci in hoa, mi lp chn ra 200 mu, nh vy b d liu VietData c tng cng 17800 mu.2.5.3.2. Kt qu thc nghim trn b d liu MNISTu tin chng ti th nghim hiu qu ca Thut ton SVMClassify trn b d liu MNIST vi cc chin lc OVO v OVR. M hnh SVM c s dng vi hm nhn Gauss v cc tham s C = 10 (tham s hm pht), Cache = 1000 (kch thc vng nh lu tr cc vect ta).Bng 1: Kt qu thc nghim trn tp MNIST vi hm nhn RBF(s =0.08).

Kt qu thc nghim Bng 1 cho thy cc chin lc OVO v OVR u c cc u im v nhc im ring. Chng ti so snh hiu qu phn lp ca SVM so vi phng php s dng m hnh mng n ron 4 lp (144 n ron lp vo, 72+36 n ron cc lp n, 10 n ron lp ra) [5.4] trn cng mt b d liu chun MNIST (Bng 2).Bng 2: So snh kt qu nhn dng ca VM vi m hnh mng n ron.

Kt qu Bng 2 cho thy kt qu nhn dng theo m hnh SVM c chnh xc cao hn so vi m hnh mng n ron, tuy nhin tc nhn dng ca SVM th chm hn.2.5.3.3. Kt qu thc nghim trn d liu ch vit tay ting Vit.Vic thc nghim trn d liu ch vit tay ting Vit c tin hnh theo phng thc thm nh cho (Cross-Validation). B d liu VietData c chia thnh k phn ( y k c chn =10), sau s dng k-1 phn hun luyn v 1 phn cn li nhn dng, qu trnh c ny c lp i lp li k ln. Cc kt qu thc nghim c th hin trn Bng 3.Kt qu thc nghim Bng 3 cho thy tc phn lp ca SVM i vi bi ton phn a lp l qu chm, khng th p ng c i vi mt h thng nhn dng thi gian thc. V vy, cn phi c nhng gii php ph hp tng tc cng nh chnh xc phn lp i vi d liu ch vit tay ting Vit.Bng 3: Thc nghim trn tp d liu ch vit tay ting Vit.

2.5.4. nh gi hiu qu phn lp SVMp dng phng php phn lp SVM vo bi ton nhn dng ch vit tay ri rc, chng ti c mt s nhn xt sau y:- SVM l mt phng php hc my tin tin c c s ton hc cht ch v t chnh xc phn lp cao. Tuy nhin, hn ch ln nht ca SVM l tc phn lp chm, ty thuc vo s lng vect ta thu c sau khi hun luyn. Mt hn ch khc ca SVM l pha hun luyn i hi khng gian nh ln, v vy vic hun luyn i vi cc bi ton c s lng mu ln s gp tr ngi trong vn lu tr. - Bn cht nh phn cng l mt hn ch ca SVM, vic m rng kh nng ca SVM gii quyt cc bi ton phn loi nhiu lp l vn khng n gin. C nhiu chin lc c xut m rng SVM cho bi ton phn loi nhiu lp vi nhng im mnh, yu khc nhau ty thuc vo tng loi d liu c th. Cho n nay, vic la chn cc chin lc phn lp vn thng c tin hnh trn c s thc nghim.- Bi ton hun luyn SVM thc cht l bi ton qui hoch ton phng (QP) trn mt tp li, do lun lun tn ti nghim ton cc v duy nht, y l im khc bit r nht gia SVM so vi mng n ron, v mng n ron vn tn ti nhiu cc tr a phng. Bn cht ca SVM l vic phn lp c thc hin gin tip trong khng gian c trng vi s chiu cao hn s chiu ca khng gian u vo thng qua hm nhn. Do , hiu qu phn lp ca SVM ph thuc vo hai yu t: gii bi ton QP v la chn hm nhn. Vic gii bi ton QP lun lun t c gii php ti u nn mi c gng trong nghin cu l thuyt SVM tp trung vo vic la chn hm nhn. La chn hm nhn v cc tham s ca n nh th no SVM phn lp tt nht vn l mt bi ton m.- Tc phn lp ca SVM b nh gi l chm so vi cc phng php phn lp khc, ty thuc vo s lng vect ta thu c sau khi hun luyn. V vy, c nhiu cng trnh tp trung nghin cu gim ti a s lng vect ta nhm tng tc phn lp ca SVM, mt s kt qu nghin cu c gi tr v SVM c cng b trong cc cng trnh [86,5.1,5.2].Mun p dng k thut phn lp SVM vo bi ton nhn dng ch vit tay ting Vit, cn phi c nhng gii php trnh bng n s phn lp cng nh gim ti a s vect ta tng tc nhn dng.2.5.5. Kt lunPhn ny xut m hnh nhn dng ch vit tay ri rc trn c s phng php my vc t ta. Cc kt qu thc nghim cho thy m hnh ny c kt qu nhn dng chnh xc hn so vi m hnh mng n ron. Tuy nhin, khi p dng SVM vo bi ton nhn dng cng gp phi mt s hn ch nht nh: bng n s phn lp v s ng vc t ta thu c sau khi hun luyn s dn n vic phn lp chm.Chng ti s tip tc nghin cu xut m hnh hiu qu cho bi ton nhn dng ch vit tay ting Vit. Gim thiu s vc t ta ci thin tc phn lp v la chn cc tham s ca SVM cng l vn cn quan tm. Mi phng php hc my u c nhng u v nhc im ring, v vy vic kt hp, lai ghp gia cc phng php nhm nng cao hiu sut nhn dng cng l hng m cc nh nghin cu ang quan tm.

2.6. Kt hp cc k thut nhn dng Cc phn trnh by trn cho thy rng c nhiu phng php phn lp c th p dng i vi cc h nhn dng ch vit tay. Tt c cc phng php trn u c nhng u im v nhc im ring. Vn t ra l cc phng php trn c th kt hp vi nhau theo mt cch no nng cao cht lng nhn dng hay khng? Nhiu cng trnh nghin cu kin trc phn lp theo tng kt hp cc phng php phn lp nu trn. Cc hng tip cn kin trc kt hp phn lp c th chia thnh ba nhm sau: Kin trc tun t, kin trc song song v kin trc lai ghp. 2.6.1. Kin trc tun t Kin trc ny chuyn kt qu u ra ca mt my phn lp thnh u vo ca my phn lp tip theo. C bn chin lc c bn c s dng trong kin trc tun t, l dy, chn la, boosting v thc nc. Trong chin lc v dy, mc tiu ca mi giai on l thu gn s lp m mu u vo c th thuc v cc lp . S lp c th thu gn ti mi giai on sinh ra nhn ca mu giai on cui cng [76]. Trong chin lc chn la, u tin my phn lp gn mu cha bit vo mt nhm k t gn ging nhau. Cc nhm ny tip tc c phn lp cc giai on sau theo mt cy phn cp. Ti mi mc ca cy, nhnh con cng m l ging nhau theo mt o no . V vy, cc my phn lp thc hin phn lp t th n tinh dn trong cc nhm nh [77]. i vi chin lc boosting, mi my phn lp iu khin mt s lp, cc my phn lp pha trc khng th iu khin c cc lp ca cc my phn lp pha sau [79]. Cui cng, trong chin lc thc nc, cc my phn lp c kt ni t n gin n phc tp. Cc mu khng tha mn mt mc tin cy no th phi thng qua mt my phn lp mnh hn trong mt gii hn no ca cc c trng hoc cc chin lc nhn dng khc [78]. 2.6.2. Kin trc song song Kin trc ny kt ni kt qu ca cc thut ton phn lp c lp bng cch s dng nhiu phng php khc nhau. Trong s cc kin trc ny, tiu biu nht l phng php b phiu [80] v lut quyt nh Bayes [81]. 2.6.3. Kin trc lai ghp Kin trc ny l mt s lai ghp gia hai kin trc tun t v song song. tng chnh l kt hp cc im mnh ca c hai kin trc trn v chn bt nhng kh khn trong vic nhn dng ch vit. Sau y l mt vi v d in hnh v cc hng kt hp cc k thut nhn dng: Trong [82], mt hng tip cn dy trn c s phn lp a c trng v a mc c pht trin cho ch vit tay Trung Quc. H thng ny s dng mi lp c trng nh cc c trng v hnh dng bn ngoi, cc c trng v mt nt bt v cc c trng v hng nt bt. u tin, mt nhm cc my phn lp phn chia ton b cc k t thnh mt s nhm nh hn, v vy s lng mu cn x l trong mi bc tip theo gim i ng k. Sau , phng php phn lp k t a mc c xut vi nm mc phc v cho quyt nh phn lp cui cng. Trong mc th nht, mt phn b Gausse c la chn s dng cho vic la chn mt s mu nh hn t mt vi nhm. T mc th hai n mc th nm, cc hng tip cn i snh c s dng vi cc c trng khc nhau nhn dng. Trong [83] Srihari v cc cng s xut mt hng tip cn song song cho vic nhn dng bn tho vit tay mc t, h kt hp ba thut ton: i snh mu, phn lp cu trc v phn lp hn hp gia thng k - cu trc. Cc kt qu nhn c t ba thut ton trn c kt ni li theo mt trnh t thch hp. Kt qu cho thy tc nhn dng tng ln ng k. Mt phng php lai ghp c nh gi cao do nhm nghin cu ca IBM xut [77] kt hp mng n ron v cc phng php i snh mu trong mt chin lc nhn dng y cc k t (ch hoa, ch thng, ch s v cc k t c bit). u tin, my phn lp a mng hai giai on (TSMN - two-stage multinetwork) nhn bit ba nhm: ch hoa, ch thng v ch s. TSMN bao gm mt dy cc mng chuyn dng, mi mng c thit k nhn dng mt tp con ca ton b tp k t. Mt my tin phn lp v mt b phn la chn mng c s dng kch hot cc mng chuyn dng cn dng. Sau , s dng my phn lp i snh mu i snh mu u vo vi cc mu trong ba nhm la chn bi my phn lp TSMN. Cc khong cch i snh mu c dng chn li mng nu nh TSMN khng m bo v quyt nh nhn bit ca n. 2.7 KT LUN Chng ny gii thiu mt cch tng quan v lnh vc nhn ch vit. Cho n nay cc kt qu nghin cu nhn dng ch vit tay vn cn hn ch, cc ng dng ch yu ch tp trung mt s lnh vc hp. c bit c rt t kt qu lin quan n nhn dng ch vit tay ting Vit, cc kt qu nghin cu cng ch tp trung vo ch Vit vit tay on-line [25]. C nhiu k thut tin tin ang c p dng cho bi ton nhn dng ch vit tay nh HMM, mng n ron, k-lng ging gn nht, lut quyt nh Bayes, SVM... Trong s cc k thut ny th SVM c nh gi l phng php c chnh xc phn lp cao v phng php lun ca n c xy dng da trn mt nn tng ton hc rt cht ch. CHNG III. NH GI, SO SNH CC PHNG PHP NHN DNG.

PHNG PHP NHN DNGU IMNHC IM

i snh mu L k thut nhn dng ch n gin nht da trn c s i snh cc nguyn mu(prototype) vi nhau nhn dng k t hoc t. Cc k thut i snh mu ch p dng tt i vi nhn dng ch in. i vi ch vit tay th cc k thut ny t ra km hiu qu, kt qu nhn dng ca n cng rt nhy cm vi nhiu

Phng php tip cn cu trc Da vo vic m t i tng nh mt s khi nim biu din i tng c s trong ngn ng t nhin. D thc hin cn c vo qu trnh phn tch c php Cho n nay cn nhiu vn lin quan n h nhn dng c php cha c gii quyt c lp v cha xy dng c cc thut ton ph dng.

Mngn ron Mng n ron c ng dng nhiu trong cc bi ton phn loi mu (in hnh l nhn dng) bi u im ni tri ca n l d ci t cng vi kh nng hc v tng qut ho rt cao. Vi thut ton n gin nhng rt hiu qu, cng vi thnh cng ca m hnh ny trong cc ng dng thc tin, mng n ron hin ang l mt trong cc hng nghin cu ca lnh vc hc my. Mng n ron t ra ph hp vi cc bi ton i snh, phn loi mu, xp x hm, ti u ho, lng t ho vc t v phn hoch khng gian d liu, trong khi cc phng php truyn thng khng kh nng gii quyt cc vn nu trn mt cch hiu qu. c bit trong cc h thng nhn dng s dng mng n ron t c t l nhn dng kh chnh xc, c th so snh vi cc phng php nhn dng cu trc, thng k, ,thit k v coding n gin, Tnh chm v sc xut khng cao khng c quy tc tng qu xc nh cu trc mng v cc tham s hc ti u cho mt (lp) bi ton nht nh. Tiu chun thu thp c s d liu hun luyn cn kht khe. Do , h thng c th ng dng trong thc t cn phi ni lng hn na cc tiu chun ny.

M hnh Markov n (HMM - Hidden Markov Model) Phng php m t ng bin t b nh hng bi kch thc ch cng nh m, nht ca nt ch, t b tc ng bi nhiu trn ng bin. Vic s dng cc HMM kh nhiu v trch chn c trng cho kt qu tt, vi thi gian thc hin chp nhn c. T vic c t c cu trc, bng k thut phn lp v m ho mi lp bng mt m hnh nhn dng. C s d liu cc m hnh nhn dng c kh nng t ng loi b s d tha, gim thiu thi gian truy xut, t tc tng i tt trong cc th nghim, xc sut cao, coding n gin, khng dng nhiu b nh. Cc thut ton d bin thng rt nhy cm khi ch b dnh nt hay t nt, khc phc iu ny, h thng phi c kh nng lng trc nhng nt c th b dnh hay b t a ra mt mu ph dng trong trng hp mu nhn dng b dnh nt hay t nt. Phng php ny ch c gng m t tt nht cu trc ch m cha ch n kch thc, iu ny khin cho h thng d nhm ln ch hoa v ch thng, nht l i vi nhng k t m vit hoa hay vit thng ch khc nhau v mt kch thc nh ch `c` v `C`, `x` v `X` ... .Nhc im l rt kh phn lp d liu.

Phng php my vc t ta (SVM support vector machies) SVM c nh gi l mt hng tip cn phn lp t chnh xc cao. phng php hc my tin tin ng gp nhiu thnh cng trong cc lnh vc khai ph d liu cng nh trong lnh vc nhn dng. Bi ton hun luyn SVM thc cht l bi ton QP trn mt tp li, do SVM lun c nghim ton cc v duy nht, y chnh l im khc bit r nht gia SVM so vi phng php mng n ron, v mng n ron vn tn ti nhiu im cc tr a phng. Hn ch ln nht ca SVM l tc phn lp rt chm, ty thuc vo s lng cc vc t ta. Mt khc, giai on hun luyn SVM i hi b nh rt ln, do cc bi ton hun luyn vi s lng mu ln s gp tr ngi trong vn lu tr. Hiu qu phn lp ca SVM ph thuc vo hai yu t: gii bi ton QP v la chn hm nhn.

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