TuyIn tap Cong trinh Nghien ciru Cdng nghe Thdng tin va Truyen thdng 2010
RUT TRICH DAC TRU>JG DlTA VAO DO NHAT QUAN
H U ' 6 N GCHO PHAN LOfP ANH DAU VAN TAY
Le Hoang Thai', Van Thien Hoang^
'Khoa Cdng Nghe Thdng Tin, Trudng Dai hpc Khoa Hpc Tu Nhien Thanh phi Hd chi Minh, Viet Nam
^Khoa Cong Nghe Thdng Tin, Trudng Dai hpc K)> Thuat Cdng Nghe Thanh phd Hd chi Minh, Viet Nam [email protected], [email protected]
Tom tat. Phan ldp anh la mdt giai doan quan ttpng va nhilu thach thtic ttong qui ttinh xtJr ly nhan dang dau van tay. Muc dich ctia viec phan ldp la thu hep khdng gian tap anh cho giai doan so khdp. Trong bai bao nay, chting toi trinh bay mot phuang phap nit trich Vector dac trung Ting Hgp mdi (gpi tat la VTH) de phan loai hieu qua cac anh van tay (bao gdm ca trudng hgp anh vay tay bj mat mat thdng tin). Thue chat, ky thu§t nay tinh toan trudng nang lugng phan ldp dua vao sir ket hgp giira nang lugng trudng hudng (dac tnmg cau tnic dudng van) vdi gia tri dp nhat quan hudng (mieu ta muc dp cac hudng ciia nhQng viing lan can nhat quan theo mpt hudng thong tri). Tiep theo, mpt ludi hmh vudng dugc dat len tten trudng nang lugng phan ldp (tam dat tai diem tham chilu va canh theo hudng tham chieu) de xay dung vector dac trung VTH bit bien (dii vdi phep xoay va phep tinh tiin). Bp phan ldp Support Vector Machine-SVM se thao tac tren_ vector VTH de phan loai cac van tay. Ket qua thue nghiem tten ca sd dO lieu chuan qudc te FVC2004 cho thay hifu qua ciia phuang phap de xuat.
Tir khoa: Phan ldp anh; dp nhat quan hudng; tnrdng hudng; nhan dang anh van tay.
FEATURES EXTRACTION BASED ON ORIENTATION CONSISTENCY FOR FINGERPRINT CLASSIFICATION
Abstract. Fingerprint classification is an important and challenging stage in fingerprint recognition because of the complex search of large database. The purpose of this step is to narrow down the search space of fine matching. In the paper, we present a novel method of synthesis feature vector (called VTH) to effectively classify the fingerprint images (including even poor quality fmgerprint images). Actually, this technique computes classification energy field based on combining orientation field energy (ridge structure feature) with orientation consistency value (describes how well the orientations over a neighborhood are consistent with the dominant orientation). Then, a square grid was placed on classification energy field (its center point locates at the reference point and it aligned based on reference orientation) to construct invariant feature vector VTH (for rotation and ttanslation). Support Vector Machine-SVM will process vector VTH to classify fingerprint images. The experimental results on the FVC2004 database show the effectiveness and superiority of the proposed method.
Keywords: image classification; orientation consistency; orientation field; fingerprint recognition.
TuyIn tap Cdng trinh Nghien cuu Cdng ngh? Thdng tin va TmyIn thdng 2010
RUT TRICH DAC TRlTNG D^A VAO DO NHAT QUAN HU^dNG CHO PHAN L 6 P A N H DAU VAN TAY
Le Hoang Thai Khoa Cdng Nghe Thdng Tin Trudng Dai hgc Khoa Hgc Tu Nhien
Thanh phd Hd chi Minh, Viet Nam [email protected]. vn
Tom t&t— Phan ldp dnh \k mdt giai doan quan trong \k nhilu thach thurc trong qui trinh xir 1^ nhan dang diu van tay. Muc dich cua vi^c phan ldp la thu hep khong gian tap anh cho giai doan so khop. Trong bai bao nsiy, chiing tdi trinh bdy mpt phuonn^ phap riit trich Vector d3c ttung Tong Hgp mdi (goi tat la VTH) dl phan loai hi^u qua cac anh van tay (bao gom ca trudng hgp anh vay tay bj mat mat thong tin). Thue chat, ley thuat ndy tinh toan trudng ndng lugng phan Idp dua vao su ket hgp gifi'a nang lugng trudng hudng (ddc trung cau ttuc duirng vdn) vdi gia tri dg nhat quan hudng (mieu td muc dp cdc hudng cua nhung viing idn c|n nhat quan theo mpt hudng thong tr}). Tiep theo, mpt luoi hinh vudng dugc ddt len tren trudng ndng lugng phan lop (tdm ddt tai diem tham chieu vd canh theo hudng tham chieu) de xdy dijrng vector ddc trung VTH bat bien (doi vdi phep xoay vd ph^p tjnh tiin). B§ phdn Idp Support Vector Machine-SVM sS thao tac tren vector VTH de phan loai cdc vdn tay. Ket qud thyc nghifm tren co' sd dfr lifu chuan quoc te FVC2004 cho thay hifu qud cua phuorng phdp de xu4t.
rir khoa— Phan ldp dnh; dp nhat qudn hu&ng;
trirdmg hu&ng; nh^n dfng anh van tay.
I. G i d l T H I f U
Dac tiimg sinh ttic hgc van tay da va dang duoc sir dung rdng rai cho nhan dang ca nhan ttong nhieu linh vuc thue tl khac nhau: kl ca ttong dan su ciirig nhu thuomg mai. Tinh bit biin va duy nhit cua diu van tay iing vdi tiing ca nhan la ly do chinh cua viec ap dimg nay. v l mat iing dung, cd hai kieu he thdng nhan dang diu van tay: he thdng xac thue va he thdng tiny tim. Trong he thdng xac thue, diu vao la anh van tay va dinh danh (ID). He thdng se xac nhan xem lieu ID nay cd nhit quan vdi anh van tay tuong iing hay khdng. Diu ra la cau tta ldi diing (nhit quan) hoac sai (khdng nhit quan). Trong he thdng truy tim, diu vao la mdt anh van tay truy vin. He thdng cd gang tta ldi cau hdi: Cd nhihig van tay nao ttong co sd dir lieu gan gidng vdi van tay truy van. Diu ra la mdt danh sach ngin cac van tay [1]. Cd nhilu cdng ttinh da cdng bd cho hg thdng xac thue van tay vdi dg chmh xk dat dugc kha cao. Tuy iihien, viec xay dimg he thing truy tim Anh van tay tten co sd dii lieu Idn vin la mgt thach thiic ddi vdi cac nha nghien ciiu.
Vdi myc tieu giai quylt hieu qua bai toan nay, hudng tiip c ^ so khdp da miic dugc su dung de tim
Van Thien Hoang Khoa Cdng Nghe Thdng Tin Trudng Dai hgc Ky Thuat Cdng Nghe
Thanh pho Hd chi Minh, Viet Nam vthoang(ghcnihutech.edu.vn
kiem anh dau van tay tren co sd dii lieu Idn. Cach tiip can nay gdm hai giai doan: (1) Tim kilm thd (su dung d5c trung toan cue nhu trudng hudng, dilm ndi bat (diem ldi va diem tam giac), va phuang tham chieu (hlnh 1)) vdi muc tieu: thu hep ca sd du lifu iing vien; (2) So khdp tinh (su dung cac thdng tin phan bift nhu diem re nhanh, diem ket thue hay cdn ggi chung la minutiae (hinh 1)) vdi muc tieu: tim ra mgt sd van tay gidng nhat vdi van tay truy van. 0 ^iai doan (1), phan ldp rd la hudng tiep can truyen thdng.
Vdi each tiep can nay, anh van tay dugc phan vao mdt ttong cac ldp ditih nghia trudc, chang han nhu nam ldp [13]: lap phai, lap ttai, xoan ttdn, cung d^p vacung nhgn (hinh 4a).
Cd nhilu phuong phap dugc dl xuit cho hudng tiip can nay [2-9]. Karu va Jain [2] ttmh bay ky thu$t phan ldp dya vao sd lugng va vj tti cua cac diem ndi bat. Tuy nhien, vifc phat hifn diem ndi bat thudng nhay cam vdi nhilu nen do nhat quan va dg tin cay ciia phan ldp cd till khdng dam bao. Wang [3] dua ra dinh nghia mdi vl diem ndi bat (mgt cap gdm dilm ldi va diem tam giic), ddng thdi dua vao dSc tnmg nay de nang cao dg chinh xac phan ldp. Thdng qua c4c kit qua thue nghifm cho thay: phuang phdp cua Wang van chua khic phgc dugc ttiiugc dilm ciia nhdm tac gia Karu. Msiza [4] cai tiin phuang phap ciia nhdm tac gia Karu bing each kit hgp them thdng tin tga dg hinh hgc ciia cac diem ndi bat de nang cao dg chinh xac phan ldp. Tuy nhien, uu dilm cua hudng tham chilu cho trudng hgp anh hi xoay chua dugc khai thac ttong phuang phap nay. Tiip tuc cai tiin phuang phap ciia nhdm tac gia Karu, Liu [5] de xuit thuat toan phan ldp dua vao thdng tin cue cua dilm ndi bat (dac tnmg tga do, hudng), tii dd, xay dung bd phan ldp manh dga vao Adaboost. Phuang phap nay boat ddng rit tdt ttong trudng hgp anh van tay rd.
Mdt hudng tiep can khac la dua vao trudng hudng. Cach tiip can nay khai thac \m dilm: d|c trung toan cue tnrdng hudng bieu dien diy dii eSu tnic cac dudng van. Cappelli [6] da dl xuit hudng tiip can phan ldp dua vao ciu tiiic dl chia anh vSn tay thanh nhihig vimg ddng nhat. Sau dd, dd thi ma nd bilu dien mdi hen hf giira cac vung sS dugc sir dung ttong phan ldp. Phuong phap phan ldp dvra vao dSc tiimg cau tiiic to4n cgc nay d?t dugc dg chmh xdc cao ngay ca vdi anh bj nhieu, nhung nd cd tiie ho?t
TuyIn tap Cdng ttinh Nghien ciiu Cdng nghe Thdng tin va TmyIn tfidng 2010
ddng khdng hieu qua ttong trudng hgp anh van tay hi xoay, djch chuyen bdi vi viec phan chia cac viing ddng nhat nhay cam vdi su bien ddi ciia trudng hudng.
Zhang [7] ket hgp thdng tin trudng hudng (cu thl la phuang tham chieu) vdi each tiep can dua vao diem ndi bat, nham giai quyet trudng hgp anh bi mat mat thdng tin (thilu diem ndi bat). Gidi ban cua phuang phap la chi giai quyet tdt cho trudng hgp anh van tay bj thieu mdt ttong cac diem tam giac. Li [8]
de xuat phuong phap ket hgp trudng hudng va cac diem ndi b§t bang each xay dung vector dac trung gdm hai phan: (1) tap cac he sd tai cau tnic trudng hudng; (2) cap he sd ( bieu dien gdc tao bdi diem ldi va hai diem tam giac).Vdi each tiep can nay, y nghia he sd cua cac phan ttong mdt vector la khac nhau, nen hieu qua phan ldp dua vao khoang each giira hai vector cd the khdng cao.
Diem le nh^nh
Diem
Hinh 1. Cac kieu diem dac ti\mg van tay
Gan day, cac bd phan ldp inay hgc su dung vector dac trung dudng van dugc iihieu nhdm tac gia nghien ciiu [9-13]. Jain [9] de xuit bd phan ldp hai giai doan (k-nearest neighbor va mang noron) su dung vector dac tnmg FingerCode [12]. Hudng tiip can nay tan dung cac uu diem cua cac ky thuat may hgc dl nang cao hieu qua phan ldp. Tuy nhien, vector FingerCode khdng bieu dien day dii cac thdng tin cue bd cua cac diem ndi bat, dac biet chua giai quylt tdt trudng hgp anh van tay bi xoay. Yfu dilm nay do: chi su dung duy nhit mdt ludi trdn cd tam ludi dat tai dilm tham chieu de tinh toan he sd nang lugng miic xam tai mdi vung cua anh van tay (dugc lgc bing ham Gabor theo mdi hudng da chgn trudc). Hong [10] dl nghi mdt ky thuat phan ldp van tay dimg: Vector FingerCode cho bd phan ldp SVM; vector dac tnmg (thdng tin dilm ndi bat va phuang tham chilu) cho bg phan ldp naive Bayes. Phuang phap nay da sii dung cac dac ttimg toan cue nhu hudng, dilm ndi bat, phuang tham chieu. Nhdm tac gia Hong da cdng bd phuang phdp nay dat do chinh xac cao ttong thue nghiem.
Wang [11] sit dung ludi hinh vudng, tam dat tai diem tham chilu dl nit trich vector bilu dien hudng dudng van. Sau do, tac gia su dung thuat toan k-mean de gom nhdm cac anh huin luyfn (5 nhdm). Nhdm tac gia Liu [13] su dung mdt ludi hinh ttdn cac phin
khdng diu nhau (nhinl thl hien vai trd cua cdc viing hudng: vimg biin ddi hudng nhilu ya vung it bien ddi hudng) dl nit trich vector bilu diin trudng hudng.
Sau dd, nhdm tac gia de xuit sii dung thuat todn gom nhdm nhieu cap dua vao vector dac trung hudng nay va vector khoang each dudng van. Phuong phap nay dugc cdng bd la cd kha nang thu hep dang ke khdng gian tim kiem va dat do chinh xac cao.
Nhin chung, cdc tac gia da su dung nhieu ky thuat khac nhau nham khai thac day du cac dac trung toan cue van tay iihu dac trung trudng hudng, thdng tin cue bd cua dilm ndi bat (kieu, vj tti, hudng). Dua vao y tudng tten, ttong bai bao, chiing tdi de nghj mdt phuang phdp nit trich vector dac trung hieu qua cho viec phan ldp van tay. Vector dac tnmg nay la mgt vector tdng hgp bieu dien diy du cac dac trung: nang lugng trudng hudng, dg nhat qudn hudng, diem ldi va hudng tham chilu. Trudiig hudng dugc canh chinh dua vao hudng tham chilu nham giai quylt hifu qua trudng hgp anh van tay bi xoay. Gid tri dg nhat qudn hudng bieu dien ttgng sd ddng gdp cua mdi viing hudng (viing diem ndi bat cd ttong sd ddng gdp cao ddng nghia vdi gia tri dg nhit quan hudng thap va ngugc lai). Cudi cung, bg phan ldp SVM ttong thu vien LIB-SyM [23] se kiem dinh hieu qua vector tdng hgp dl xuat ciia chiing tdi. Cac ket qua thu nghiem tten co sd dQ lifu FVC2004 cho thiy tinh kha thi ciia phuang phdp.
Trong cac phin sau, phuong phdp ciia chiing tdi dugc trinh bay chi tiet. Phan 2 triiih bay cac budc tiin xir ly can thiet cho giai doan nit trich vector dac tnmg phan ldp. Phin 3 md ta Iqr thuat nit trich vector dac trung VTH va bg phan ldp SVM. Phan 4 trinh bay chi tilt kit qua thue nghif na. Cuoi ciing, kit luan bai bdo dugc trinh bay ttong phan 5.
IL T I E N X C L Y
Muc tieu ciia giai doan tiin xii ly la nang cao chit lugtig anh van tay (giam anh hudng ciia nhilu) va chuin bi tdt cho cac giai doan xu ly sau.
A. Chudn hda dudng vdn [16]
Ggi / i,j la gid tti miic xdm tai dilm anh i,j , M va F tudng iing la gid tti tiling binh va dg bifn ddi miic xam anh / , va N i,j la gia tri mirc xdm anh da dugc chuan hda tai dilm anh i,j chuan hda dugc dinh nghia nhu sau:
Anh
N i,j =A^o + ngoai ra,
\Va I i,j -M
vdi / i,J > M,
N i,j =A/o-1
Fo / /,; -M
(1)
TuyIn tip C6ng trinh Nghien cdu Cdng nghe Thdng tin va Truyin thdng 2010
Trong dd, MQ , VQ tuong iing la gia tti trung binh va do bien ddi mong mudn ( MQ = 100, Fg = 50 ttong thue nghiem). Gia tri trung binh va do bien ddi miic xam cua anh kich thuoc MxN diem anh dugc tinh nhu sau:
1 M-l N-\
M(I) = Z Z W,J), (2)
^^ i=Oj=Q vd
1 M-\N-\ 2
V(I) = Z Z / i,j -MI (3) MN '=0 y=o
Muc dich cua giai doan nay la giam miic dg biin ddi muc xam tai dudng bien giua dudng van va ranh dl giiip cho giai doan udc lugng hudng dugc hifu qua han. Giai doan nay khdng lam thay ddi thdng tin dudng van va ranh.
Anh dugc chia thanh cac khdi cd kich thude ky.k. Gid tti miic xam trung binh cua mdi khdi dugc so sanh vdi gid tti miic xdm trung binh ciia toan anh dl chgn ra vvmg dac tnmg, phuc vu cho vifc nhan dang.
B. Tinh todn trucmg hudng [16]
Trudng hudng ddng vai ttd quan ttgng ttong phan ldp va nang cao chat lugng anh van tay. Do vay, tinh toan tiirdng hudng la mgt budc tiin xii ly cin thift.
Ggi ^la trudng hudng ciia anh van tay. 0 i,J la hudng dugc udc lugng ciia dudng van cue bd tai khdi cd tam la dilm anli i,j Cac budc df tinh todn tiirdng hudng dugc tdm tat nhu sau :
• Chia dnh van tay thanh cdc khdi vudng khdng lap nhau. Kich thude moi khdi la w x w diem anh (vv = 8 ttong thue nghifm).
• Tinh toan gia tti dg tiugt muc xdm (gradient) tiieo phuang dgc 3^ i,j va ngang
d^ i,j ciia mdi diem anh i,j Toan tii Sobel thudng dugc su dung de tinh giadient.
• l/dc lugng hudng cua mdi khdi i,j nhu sau:
0 i,j = — arctan 2
Vy U
(4) vdi
i+wl2 i+wl2 ,c\
Vy(i,j)= Z I 2dx(u,v)dy(u,v), (5) u=i-wl2 v=j-wl2
VxiU)- ' T ' T (dx(u,v)2-3y(u,v)2) (6) u=i-wl2 v=j-wl2
De lam ttan trudng hudng, hudng mdi khoi dugc tinh nhu sau.
0 i,j =—arctan 2 u,v e n s sin 2(9 u,v 2 u,v s n s '^os 261 u,v (7) vdi n * la cdc khdi vien lan can 8 vdi kich thude la 2.S+1 X 2s+l ( s = 2 ttong thue nghiem - hinh 2a).
C Tinh do nhdt qudn hudng
Do nhat qudn hudng |^15] bilu diin miic do hudng cua cdc khdi lan can nhat quan vdi hudng thing tri (hinh 4c). Ggi Con i,j,s la do nhat quan cua khoi i,j vdi cdc khdi lan can la n 5 va dugc tinh nhu sau:
Con i,j,s
' 2 2
M
(8)
ttong dd, M sd lugng khdi ttong n s thue nghifm.
5 = 3 ttong
Hlnh 2. (a) n 5 la cac khdi lan can 8 ban kinh s, (b) Utidng nh^t quan hudng ldi, va (c) anh van tay di dugc phat hi^n di£m
loi.
D. Phd! hien diim !ham chiiu
Dilm tham chilu ddng vai ttd quan ttong ttong vifc canh chinh anh van tay (phep tinh tien). Diem tham chilu la dilm ldi ndm trfn dudng van cong ldi.
Viec xdc dinh dilm tham chilu theo thuat todn dugc ttiiih bay ttong [17] nhu sau:
Tmh Dx i,J Dy i,j ^^^ j^gj j ^ ^ j ''^ bdi phuong tiinh sau:
Dx i,j = Z cos 20 i-\,j+s s=-l
1
Z cos 20 i+l,j+s s=-l
(13)
TuyIn tap Cong trinh Nghien ciru Cdng nghe Thdng tin va TmyIn thdng 2010
1 1 Dy i,j = Z sin 20 i+s,J-l - Z sin 2^ i+s,J+\
s=-l s=-l (14)
• Tinh toan nang lugng muc cong ldi CCEnergy i ,j cua mdi khdi i,j bang phuang ttinh sau:
Dx i,j +Dy i,j CCEnergy i,J = —
• Tinh toan mure do nhit qua hudng theo dudng cong ldi COCons i,j cua moi khdi
i,j bang phuang ttinh:
(15)
COCons i,J =ConsAV i,J -CCEneiy i,j
ttong dd,
ConsAV i,j 1 s
— Z Cons i,j,s
(16)
(17) s=\
E.
> Xdc djnh khdi cd dg nhat qudn theo dudng cong ldi nhd nhat COCons ip,jp la diem tham chieu (hinh 2b, 2c).
Phdt Men hudng tham chiiu
Hudng tham chieu dugc sii dung de chuan hda anh van tay khi bj xoay. Hudng tham chieu la hudng cd cac dudng van cue bd lan can song song vdi nd nhifu nhat [15]. Ggi Var k la gid tti bieu dien miic do cac hudng cue bd song song vdi hudng k dang xet. Phuoiig phap phdt hifn hudn^ tham chieu do Liu [ 15] de xuat dugc ttinh bay tdm tat nhu sau:
• Tinh gia tti Var k cho cdc hudng iing vifn k.
^'"' ^ =-77 E V^ ^ ''J -^k I
^ . ~ - A: = 0,l,...,15,
(18) ttong dd, Q^ la cdc khdi lan can nam ttong hinh chu:
nhat cd kich thude WxH khdi ( 5 x 7 ttong thue nghiem) va cd tSm tai diem tham chif u, va song song vdi hudng ^ , ( j ^ , ^ 3^^
• Xdc dinh hudng k cd gia tri For it* nhd nhat.
Xac dinh hudng
r.
k* = min Var k k •Var k
(19) VA:: Var k -Var k <0.1
NIU tdn tai k* thi hudng tham chieu la hudng trung binh nim giiia hai hudng k va
k'^, ngoai ra k' la hudng tham chilu cua anh van tay.
(c) (d)
Hinh 3. (a) cac hinh chii nhat Q^ , (b) Huong tham chilu anh lap phai, (c) Huong tham cliieu d6i voi anh vong cung d?p, bieu do
Var k (d) co mpt huong ting vien va (e) co hai huong ung vien.
m . RUT TRICH D.^C T R U N G VA
PHANL6P
A. Rut trich vector ddc tnmg tdng hop ( VTH) Van tay bao gdm cdc dudng van va cdc ranh song song vdi nhau. Dac tnnig van tay cd hai loai: dac trung toan cue (mieu ta ciu tnic van tay) va dac trung cue bd (mieu ta cdc diem chi tilt ciia dudn§ van).
Dac trung toan cue dugc su dung ttong tim kifm thd [2-13], [20] va dac tnmg cue bg dugc sir dung ttong cdc tiiuat toan so khop tinh [17-19], [1], [14]. Df ttanh nhap nhing, cin cd su tdch bift giua cdc ddc tnmg tim kifm thd va cdc dac trung so khdp tinh.
Trong bai bao nay, chiing tdi trinh bay mgt phuong phdp nit ttich Vector dac trung Tdng Hgp mdi (gpi la VTH) cho vifc phan ldp anh van tay hifu qua, ke ca anh van tay chit lugng thip. Vector VTH cho phep bieu difn day du ciu tnic toan cgc aiih van tay bao gdm: diem ndi bat, hudng tham chieu, va tnrdng huong.
Cac diem iidi bat la d|c tnmg toan cyc quan ttgng nhat dugc nhilu tac gia sur dung tton^ vifc phan ldp anh van tay [2-5]. Liu [15] dS Ak xuat dg nhit quan hudng cho viec phat hien diem ndi bat. Do do nay tat hieu qua ttong phan ldp anh van tay bdi vi no bieu dien day dii cac thdng tin cue bg ciia diem ndi b§t:
kieu, sd lugng, va vi tti (hinh 4c). Ddc bift, d9 do ndy the hifn dugc vai ttd ciia viing chiia dilm ndi bat so vdi cac vimg cdn lai, cu the tdng ttgng s6 viing chiia dilm ndi bat chilm khoang 70% tdng ttgng so ciia tat cd cdc vimg ttong dnh (hinh 5a, 5b). Ben canh dd, tnrdng hudng la thdng tin toan cgc quan ttgng dugc
TuyIn tap Cdng trinh Nghien cihi Cdng nghe Thdng tin va Truyin thdng 2010
SU dung ttong phan ldp anh vSn tay [6], [9-13] (hinh 4b). Tir dd, Tnrdng Nang Lugng Phan Ldp (TNLPL) dugc djnh nghTa la su ket hgp giua ndng lugng trudng hudng vdi gia tri do nhat qudn hudng (hinh 4d).
De gid ttj nang lugng trudng hudn| khdng bi anh hudng bdi phep xoay va dich chuyen, thi trudng hudng tai mdi khdi dugc canh theo hudng tham chilu. Ggi 9^ la hudng tham chilu. Vi 6*,. e[-;r,;r]
va 0 j J G[-;r/2,;r/2] nen hudng moi khdi sau khi canh 6, •. duoc tinh nhu sau: ',j
I,]
A0 :-7il2<^0<nj2, hO-JT : h0>7rl2, S0+TC : h0<-7tl2
(20) vol.
^0 = 0,-01J (21)
Trong dd, A^ la do Ifch giira hudng 0 ^j vdi hudng tham chilu ^r.Kit qua la 0.. 6[-;r/2,;r/2].
Cho viec xay dimg vector A&c trung bat bien (ddi vdi phep xoay va phep tinh tien) tten trudng nang lugng dnh dugc lgc bdi ham Gabor, Liu [13] sir dgng ludi ttdn vdi cdc phin khdng diu nhau, tam tai dilm tham chieu va canh theo phuang tham chieu (hinh 5c). Tuy nhien, ludi ttdn nay khdtig bieu dien dugc nhieu vai ttd cua viing chiia diem ndi bat.
Hinh 4. .) Anh dilm tham chilu va phuong tham chilu, b) truong biin d6. htrong, c) tmong dg nhat quan huong va d) mrong nang lugng phan lop cua cac anh ung voi kieu lap phai, lap trai. xoan tron, cung d?p va cung nhgn.
TuyIn tap Cong trinh Nghien ciiu Cdng nghe Thdng tin va Truyin thdng 2010
Bdi vi nang lugng TNLPL da bieu dien dugc ttgng sd ddng gdp ciia cdc viing khde nhau, nen chiing tdi su dimg mgt ludi hinh vudng vdi cac d deu nhau dl nit ttich vector dac trung tit trudng nang lugng nay. Tam ludi hinh vudng dat tai dilm tham chilu. Canh ludi song song voi hudng tham chieu.
Hudng tham chilu cit ddng cudi cdng cua ludi (hinh 5d). Ggi x^,y^ la tga do diem tham chieu. E la canh cua ludi w^ la kich thuoc cua mdt d vudng.
Ggi Xi,yj la tga do tam cua khdi i,j Ggi IJ/1^ la tap cac khdi d ddng / va cgt m ciia ludi d vudng. If/, ^ dugc djnh nghia nhu sau:
ij/^^ = i^J \0<l =x,m=y<E,0<Xi <N,0<yj <M (22)
x = dxsin <p /w£ + El2, y = dxcos <p Jw^+Ell,
^ = tan 1 y-i-yr ^ \-0^moA27r,
^ = >/T
+ yt-yrttong dd, cac he sd £ , Wg dugc chgn tii thue nghifm sao cho dilu chinh can ddi giira do chinh xac vd tdc do thue hien. Vi du, anh van tay cd kich thuoc 300x300 va kich
lliii
10(M> 1 • 0 1-0 2 • 0 2<> ) • 0 »^4 • 0 4 0 S 10 S-0 6 • 0 64) 7 • 0 7-0 S > 0 8-0 9 SO 9 1
b) c) d)
Hinh 5 a) Trong so ting voi dp nhat quan huomg cvia moi vvmg tren anh van tay, b) Ti le tong trong so dong gop tuong img voi timg khoang gia tri so voi tong trong so tit ca cac vung. Minh hoa sii dung kham tron (c) de nit trich vector dac tnmg hucmg [8] va sir dung kham vuong
(d) de nit trich vector dac tnmg VTH.
thude mdi khdi w = 1 0 , thi ma ttan hudng cd kich thude la 30 x 30. Do dd, viec chgn £ = 10 va W£ = 30 (hay mdt d vudng ciia ludi chiia 9 khdi) se tao ra ludi cd kich thude la 10 x 10 hay vector dac trung cd kich thude la 100. Kich thuoc nay cho phep phan ldp van tay vdi tdc do rit nhanh.
Ggi 9= v^,V2,...,Vp vdi P = ExE la vector dac trung VTH cin xay dung. Vector S dugc tinh nhu sau.
Vi=^i^„,i = lxwE+m,
^ / „ = — y TNLPL ' ^^^^
vol
A',,,
"." ev',^
TNLPL^^ = l-Consiu,v) xsm 0^^ (24) ttong dd, TNLPL „^ la nang lugng TNLPL tai khoi
u,v , N^ la sd lugng khdi thugc d ludi (^,„ , O , ^ la tnmg binh nang lugng TNLPL tai d ludi
l,m Theo cdng thiic 24, gia tii TNLPL tiiugc khoang tii -1 den 1. Trudng hgp nhfin^ d ludi d ngoai vdng ddc tnmg (do dnh cd mgt phan), thi gia tri 0 1 ^ dugc tinh bdng phuang phdp ngi suy sir dung phan phdi Gaussian rdi r^c.
Tuyen tap Cdng ttinh Nghien cuu Cdng nghe Thdng tin va Truyin thong 2010
Theo cdng thiic 23, gia ttj moi thanh phin ciia vector 9 thugc khodng tit -1 din 1. Phin tiip theo chiing tdi ttinh bay viec dp dung bd phan ldp SVM sii dung cdc vector tdng hgp VTH da ttinh bay cho phan loai dnh diu van tay.
B. Phdn lap dnh
SVM la bg phan ldp nhj phan dugc su dung phd bien trong ITnh vuc xu ly anh. Ky thuat nay dnh xa miu diu vao sang mien khdng gian dac trung nhilu chilu ban va tim ra mat phang tdi uu cho phep tdi tilu loi nhan dang iing vdi bg du lieu huin luyfn su dvmg ham tdch ldp phi tuyen.
LIB-SVM ' la thu vifn bd phan ldp SVM. Trong thu vifn nay, chiing tdi su dung bd phan ldp C-SVC cho hudng tiip can phan ldp iihi phan va hudng tiip can phan nhieu ldp vdi co chd "mgt - mdt"
1) Phdn lap C-SVC (trudng hap nhi phdn) Cho tap vector x, e R",i = 1,...,/, thugc hai ldp, tuang ling la vector yeP' vdi >',• e 1,-1 , C-SVC giai quyet bai toan gdc sau:
. 1 T
tmn —w w +
«,b,4 2
^Z^^
(25)1=1
sao cho
yi w^^ X,. +ft > 1 - ^ . ,
^ , > 0 , / = l /.
Ddi ngiu ciia bai toan (25) la bai todn qui hoach toan phuang:
mm —a^Qa-e^a a 2
(26) sao cho
T
y a
la
0,
0<a,. <C, (=1,...,/, Trong dd, ela mdt vector, C > 0 la can tten, Q
ma ttan nhan kich thude Ixl vdi Qy=yyjKxi,Xj vk K Xi,Xj ^^ x/<!> Xj la T
nhan. d day, vector huin luyen x, dugc dnh xa sang miln khdng gian nhilu chieu ban bang ham ^ . Bang 1 tiinh bay mgt sd ham nhan K x,Xi
Thu vifn [23] dugc phdt triin bdi BO mon khoa hpc va ky thu?t mdy tinh, trudng D?i hgc qudc gia Dai Loan, 106 Ddi Bdc, Dai Loan (http://www.csie.ntu.tw/~cjlin).
BANG 1 MOT s6 HAM NHAN SVM.
Tuyen
tinh Da thiTC Gaussian Sigmoid
xjCj +y e x p
h-4
2a^
| 2 ^
tanh xjij +Y
Mdt mau x se dugc phan ldp nhi phan theo ha m quyet dinh cd dang.
f X =sgn ^yiOiK x„x +b (27)
2) Phdn nhiiu lap
Cd nhieu phuang phap df xuit cho vifc md rgng S\'M cho trudng hgp nhieu ldp. Cd hai phuang phdp thdng dung: "mgt - mgt" va "mgt - tit ca" [21-23].
Thu vifn LIB-SVM sir dvmg hudng tiip can "mgt - mgt" Trong dd, k k-\ 12 bg phan ldp dugc xay dvmg va moi bg phan ldp huan luyfn du lifu hai ldp khde nhau. Xet dir lifu huan luyen tir hai ldp i, j . chiing tdi gidi quylt bai todn phan ldp nhi phan nhu sau:
Sao cho
T
min - wv ^JJ-t-Cy 4'
^.b«,i" 2 j ^ ' (28)
HA ^ X, l+b'-' >l-^i' nfu X, tiiugcldp /' -J^ ^ X, +6'-' S - l + ^ f nlu X, thugc ldp
# f > 0,1=1,...,/.
Trong phan ldp, co chl bin chgn duac su dgng:
mdi bd phan ldp nhi phan dugc xem xet dk bau chgn, mlu dau vao thugc ldp cd gid tri bau chgn cao nhat.
IV. KETQUATHV'CNGHI$M Phuang phdp cua chiing tdi dugc thue nghifm tten CO sd dO lifu quoc tl FVC2004. Co sd dd lifu nay cd 3200 dnh van tay (phan Idn dnh chit lugng thap). Cdc dnh dugc phan loai bdi cac chuyen gia tiianh 5 ldp khdng diu nhau. Dk danh gid chinh xdc, chiing tdi chgn cac ldp vdi sd anh deu nhau la 416 anh dl kilm tta va chgn 20% sd anh mdi ldp de huin luyfn. Tiip theo, thuat todn dl xuat se phan loai cdc aidi van tay nay. Bd phan ldp C-SVC su dung ham nhan Gaussian vdi a^ = 0.05. Kit qua phan ldp van tay dugc trinh bay ttong bang 2.
TuyIn tap Cong trinh Nghien ciiu Cdng nghe Thdng tin va Trayin thdng 2010
BANG 2 MA TRAN KET QUA THl/C NGHlfM NAM LCiP TREN CO sd DlJ LIEU FVC2004
Lop thyc te Xoan Tron Lap Irdi Lap phii Cung nhpn
Cung dfp
Ldrp duffc giao Xoan
Tron 399 3 4 4 1
Lap trai 7 407
0 7 4
Lap phai 5 0 404
9 3
Cung nhon 3 6 7 382
15
Cung dfp
2 0 1 14 393 95.43%
Nhm vao bang 2, cd tat ca 1985 dnh dugc phan ldp chinh xac va 95 anh phan ldp nham. Bang 2 cho ket qua dat do chinh xdc phan ldp la 95.43 %, dg chinh xac dugc dinh nghTa iihu sau.
AR= — x\QO.
T (29)
trong dd, AR la do chinh xac phan ldp, M la tdng sd anh phan ldp chinh xac (tdng cac sd tten dudng cheo ma tran ket qua phan ldp), T la tdng sd anh cin phan loai.
Hinh 6 minh hoa anh thuoc 6 lop trong co so NIST4 (a) va co so da heu FVC2004 (b).
Phuang phap cua chiing tdi da dugc so sdnh vdi cac hudng tiep can cua nhirng tac gid khac. Cu thl, nhdm tdc §ia Msiza [4] sir dvmg co sd dir lifu FVC2002 de kiem tra. Thuat toan phan ldp cua nhdm tac gia Msiza dat do chinh xdc 83.5% . Co sd du lifu FVC2004 la phien ban nang cip ciia co sd dir hfu FVC2002. Anh ttong ca sd dir lieu nay mit mat thdng tin nhilu hon so vdi co sd dii: lifu FVC2002 [24]. Do vay, ket qua cua phuong phdp chiing tdi cd ti'nh kha thi cao hon so vdi nhdm tdc gia Msiza. Theo md ta tai hfu [24] va tai lieu [25], do khd cua dnh ttong ca sd du lieu FVC2004 va co sd dir lifu NIST 4 la tuong duong (hinh 6). Do dd, so sdnh kit qua thue nghiem cua chiing tdi 95.43% vdi kit qua tdt nhit tten CO sd du hfu NIST4 94.9% (do tac gia Liu [5]
cdiig bd) cho thay tinh kha tiii cua phuong phdp de xuat.
Chuong trinh cai dat dugc chay tten mdy tmh Intel Core2Duo 1.8 GHz. Vdi moi van tay dugc kilm tta, thdi gian xu ly phan loai tiling binh la 420 ms.
V. KET LUAN
Trong bai bdo nay, mgt thuat todn nit trich vector dac trung mdi dugc trinh bay cho viec phan ldp hifu qua anh dau van tay. Vector dac trung phan ldp nay dugc xay dimg dua vdo sir ket hgp cdc thdng tin toan cue: trudng hudng, do nhat qudn hudng, diem tham chieu, hudng tham chieu. Do vay, vector dac tnmg nay bieu dien day du nhCng dac trung phan ldp nhu:
diem ndi bat (gdm thdng tin kieu, sd lugng, vi tri, hudng), va cau tnic dudng van. Hon nGa, vector dac trung nay bit biin ddi vdi phep xoay vd phep dich chuyen. Vector dac trung dugc phan ldp bdi SVM.
Thue nghifm su dving thu vifn LIB-SVM [23] va ca sd do lifu chuin qudc te FVC2004. Kit qua thue nghifm cho thay tinh khd thi cua kT thuat df xuat.
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