do an tot nghiep nhan dang van tay
TRANSCRIPT
Mc lc
Mc lc............................................................................................................... i Danh mc cc hnh v...................................................................................... iv Danh mc mt s thut ng thng dng....................................................... vi Li ni u ...................................................................................................... vii 1. Gii thiu....................................................................................................... 1 2. Vn tay trong sinh trc hc ........................................................................... 42.1. V tr ca nhn dng vn tay trong sinh trc hc ................................................................ 4 2.2. Uniqe l mt thuc tnh ca vn tay..................................................................................... 5 2.3. Hnh thc th hin v cc c t ca vn tay....................................................................... 5 2.4. Kh khn gp phi khi nhn dng vn tay .......................................................................... 7
3. i cng v nh s v x l nh trong Matlab ........................................... 83.1. i cng v nh s .............................................................................................................. 83.1.1. Biu din nh s............................................................................................................................8 3.1.2. C s v mu ................................................................................................................................9 3.1.3. Chuyn i mu..........................................................................................................................12
3.2. X l nh s trong Matlab.................................................................................................. 133.2.1. Histogram ...................................................................................................................................13 3.2.2. Phn ngng cc b ....................................................................................................................14 3.2.3. Bin i Fourier-2D ri rc .........................................................................................................15 3.2.4. Lc nh Sobel .............................................................................................................................16 3.2.5. Pht hin bin bng ton t gradient ............................................................................................18 3.2.6. Loang rng v thu nh i tng.................................................................................................20
4. S khi thit k h thng nhn dng vn tay ......................................... 224.1. Cc nguyn l nhn dng vn tay ...................................................................................... 22 4.2. H thng nhn dng vn tay............................................................................................... 23 4.3. Xy dng h thng nhn dng vn tay bng nh s .......................................................... 24
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5. Tp mu nh vn tay ................................................................................... 26 6. Trch chn minutiae cho i snh vn tay .................................................. 286.1. Chun ha nh u vo ...................................................................................................... 296.1.1. Chun ha kch thc nh ...........................................................................................................29 6.1.2. Cn bng cng sng ca nh.................................................................................................29
6.2. Tng cng nh cht lng nh......................................................................................... 306.2.1. Tng cng nh bng cn bng histogram ...................................................................................30 6.2.2. Tng cng nh bng bin i Fourier-2D...................................................................................31
6.3. c lng orientation image v khoanh vng nh vn tay............................................... 326.3.1. c lng orientation image .......................................................................................................32 6.3.2. Khoanh vng nh vn tay ............................................................................................................34
6.4. Trch chn minutiae ........................................................................................................... 356.4.1. Nh phn ha v lm mnh ng vn .........................................................................................36 6.4.2. Pht hin minutiae.......................................................................................................................37 6.4.3. c lng khong cch ng vn..............................................................................................39
6.4. Hiu chnh ng vn v lc minutiae sai ......................................................................... 396.4.1. Hiu chnh ng vn v lc minutiae sai cp mt.......................................................................39 6.4.2. Lc minutiae sai cp hai v to m t minutiae ............................................................................41
7. Phn loi kiu vn tay ................................................................................. 437.1. Trch chn c tnh............................................................................................................. 44 7.2. To vec-t c tnh ............................................................................................................. 45 7.3. Khu phn loi kiu vn tay............................................................................................... 46
8. i chiu vn tay nh danh mu.......................................................... 488.1. Khp mu hai mu vn tay ................................................................................................ 49 8.2. i snh vn tay.................................................................................................................. 50
9. Tng kt v hng pht trin ...................................................................... 529.1. Kt qu ca n ............................................................................................................... 52 9.2. Nhng kin thc bn thn thu c .................................................................................. 53 9.3. Nhng hn ch ca n ................................................................................................... 53 9.4. Hng pht trin ................................................................................................................ 53
Ti liu tham kho .......................................................................................... 55 ii
Ph lc ............................................................................................................ 56Danh sch cc script file khc trong n ............................................................................... 56 Cc bc chy phn mm m phng ........................................................................................ 57
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Danh mc cc hnh vHnh-1. Mt s tn hiu sinh trc hc c bn ..................................................... 4 Hnh-2. ng gp ca cc ngnh trong sinh trc hc.......................................... 4 Hnh-3. Vn tay th hin cp very-fine ....................................................... 5 Hnh-4. Vn tay th hin trong cp global ..................................................... 6 Hnh-5. Hai dng minutiae quan trng................................................................ 7 Hnh-6. Biu din nh s .................................................................................... 8 Hnh-7. Cm nhn ca cc t bo nhy sng trong vng mc mt ...................... 9 Hnh-8. T hp mu. ........................................................................................ 10 Hnh-9. H ta mu ..................................................................................... 11 Hnh-10. Phn tch lc xm ....................................................................... 14 Hnh-11. Gi tr ngng ti u. ........................................................................ 15 Hnh-12. Cc bc thc hin lc nh trong min tn s ................................... 16 Hnh-13. Cc bc lc nh bng ton t khng gian ........................................ 17 Hnh-14. Biu din mask.................................................................................. 18 Hnh-15. Loang rng i tng ........................................................................ 20 Hnh-16. Thu nh i tng ............................................................................. 21 Hnh-17. To m vn tay .................................................................................. 22 Hnh-18. S khi h thng nhn dng vn tay ............................................. 24 Hnh-19. Cc loi vn tay................................................................................. 26 Hnh-20. Thut ton trch chn minutiae .......................................................... 28 Hnh-21. Tng cng nh................................................................................. 30 Hnh-22. c lng orientation image ............................................................. 33 Hnh-23. Khoanh vng nh vn tay .................................................................. 35 Hnh-24. Thng s ca hai dng minutiae quan trng....................................... 36 Hnh-25. Nh phn ha v lm mnh ng vn .............................................. 36 Hnh-26. Pht hin minutiae ............................................................................. 38 iv
Hnh-27. S minutiae pht hin c ............................................................... 40 Hnh-28. Lc cc minutiae ............................................................................... 40 Hnh-29. Cc minutiae c trch chn cui to m .................................... 41 Hnh-30. Nm kiu vn tay trong thc t.......................................................... 43 Hnh-31. S khi m t thut ton phn loi vn tay ................................... 44 Hnh-32. Phng php ch s Poincar............................................................. 44 Hnh-33. Ly c tnh cho phn loi................................................................. 46 Hnh-34. Kt qu cy quyt nh ca bi ton phn loi kiu vn..................... 46 Hnh-35. ng cong sai s hc v kim tra.................................................... 47 Hnh-36. i chiu vn tay da trn c s minutiae ......................................... 48 Hnh-37. Khp mu tng i tng.................................................................. 49 Hnh-38. Thc hin matching........................................................................... 50 Hnh-39. Kt qu nhn dng............................................................................. 51 Hnh-40. Ca s giao din. ............................................................................... 57 Hnh-41. M mt file nh................................................................................. 57 Hnh-42. Cn bng lc xm....................................................................... 58 Hnh-43. Bin i Fourier ri rc v cn bng cng sng. ......................... 58 Hnh-44. Nh phn ha nh............................................................................... 59 Hnh-45. Trng nh hng. .......................................................................... 59 Hnh-46. Segmentation..................................................................................... 60 Hnh-47. Pht hin core.................................................................................... 60 Hnh-47. Lm mnh ng vn........................................................................ 61 Hnh-48. Lc minutiae. .................................................................................... 61 Hnh-49. Hin th minutiae............................................................................... 62 Hnh-50. i snh vn tay................................................................................ 62
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Danh mc mt s thut ng thng dng trong nhn dng vn tay Ridge: ng vn tay trn ngn tay ngi. Vallay: ng rnh xen k hai ng vn tay. Singular: im k d ca vn tay trn ngn tay ngi, mang c im phn loi. Core: im tm ca vn tay, l mt trong nhng im singular. Minutia: im c trng ca vn tay trn ngn tay con ngi. Termination: im kt thc ca ng vn, mt loi minutia quan trng. Bifurcation: im tr ba ca ng vn, l mt loi minutia quan trong. Sweat pores: Vng xuyn xp lin tip to thnh ng vn (thng quan st c khi nh vn tay phn gii cao: > 1000dpi). Orientation Image: Hnh nh th hin cc nh hng cc b ca cc ng vn tay, bao gm nhiu phn t qij [0, p ] ti cc im [i,j]. Direction Image: Tng t nh Orientation Image nhng qij [0, 2p ] . Segmentation: Phn nh gia vng nh th hin ng vn v vng nh nn. Varance field: Mt cc th hin vng nh th hin ng vn cn th. Crossing number: Mt phng php dng pht hin minutiae. Poincar: Mt phng php dng pht hin core theo trng vec-t v ng bao. Ridge map: nh en trng ch th hin cc ng vn mu trng nhng khng nht thit cc ng vn c rng ng u. Thinned ridge map: nh en trng th hin cc ng vn mu trng nhng nht thit cc ng vn c rng ng u 1pixel
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Li ni uHin nay, vic thu thp, x l thng tin qua nh nhn bit i tng ang c quan tm v ng dng rng ri. Vi phng php nay, chng ta c th thu nhn c nhiu thng tin t i tng m li khng cn tc ng nhiu n i tng nghin cu. Mt trong nhng nhm ng dng hay gp trong x l thng tin bng hnh nh l xc minh hoc nh danh mu. Nhn dng vn tay l mt bi ton c th m cn phi gii quyt mt trong hai vn nu trn: xc minh vn tay (fingerprint verification) hoc nh danh vn tay (fingerprint identification). Qua tm hiu thc t em chn ti: Thit k h thng nhn dng vn tay t nh s. ti ny c ni dung bao trm ln c cc h thng c kiu nhn nhn dng verification (cn m PIN cng vi nh vn tay). Do ti c tnh cht mi, trong qu trnh lm n em gp rt nhiu kh khn. c s gip , ch bo tn tnh ca TSKH. TRN HOI LINH em dn dn tip cn c ti lnh vc ny v bc u t c mt s cc kt qu (phn loi c hn 90% cc kiu vn tay v nh danh c vn tay). Sau thi gian 15 tun khn trng thc hin n tt nghip, ti c hon thnh ng k hoch. Em mong nhng thiu st ca em trong n s nhn c nhng kin ng gp qu bu ca cc thy, c cng cc bn sinh vin. Em xin chn thnh cm n TSKH.TRN HOI LINH. Thy tn tnh ch bo em rt nhiu. Cc thy c gio trng i Hc Bch Khoa, b mn K thut o v Tin hc cng nghip cho em nhng kin thc, kinh nghim, cng nhng bi hc gip trng thnh hn trong qu trnh hc tp trng. Xin cm n bn b, ngi thn, gia nh ng vin, gip v l ch da vng chc cho em trong qu trnh hc tp, lm n. vii
Xin cm n Cng ty TNHH Tin hc v in t Thng Long cng ch V QUANG THNH to iu kin gip , cho em nhiu li khuyn b ch trong qu trnh thc tp tt nghip v lm n. H Ni, ngy 20 thng 5 nm 2007 Sinh vin thc hin
Ng Hng Vit
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1. GII THIU
1. Gii thiuNhn dng vn tay l mt b phn ca nhn dng sinh hc. Khoa hc nhn dng vn tay cng hnh thnh t kh lu. Nhng ti thi gian gn y, cng vi s ra i ca my tnh n mi t c nhiu kt qu quan trng v tr thnh mt trong nhng phng php sinh trc c tin cy nht. nh vn tay dng nhn dng thng b nh hng nhiu bi iu kin thu thp s liu (hnh nh vn tay khng trn vn, b xoay gc, mo hay c nhiu nhiu) nn vic so snh trc tip hai mu vn tay s rt phc tp v kh khn. Do vn tay cn lc nhiu, sau to m t mt s cc c tnh ca n (c th phn bit vi vn tay khc) nhm mc ch gii quyt vn x l, lu tr vn tay vi s lng ln m vn m bo chnh xc. Cc k thut thc nhn dng vn tay cng c kh nhiu. Tu trung, qu trnh ny tri qua ba cng on chnh: thu nhn vn tay (i); trch chn c tnh vn tay (ii); i snh vn tay (iii) [1]. Bi v ngay trong tng cng on ny li c nhiu bin php khc nhau, ty vo ng cnh v vng ng dng cc khu ny s thc hin theo cch c th. Cng ngh nhn dng vn tay ngy nay t ti chnh xc rt cao. Tuy vy, cc h thng nhn dng AFIS (Automated Fingerprint Identification Systems) vn cn nhiu mt hn ch. Chng hn nh IAFIS ca FBI c c s d liu ln ti hng trm triu vn tay, thi gian tm kim tnh bng pht cho mt mu, tin cy cao nhng l mt h thng s gm nhiu my tnh x l song song v gii hn trong gim nh hnh s. Trong ng dng dn s, cc h thng nhn dng thng c gii hn mt mc t phc tp hn: s mu khng ln (khong vi nghn), cu trc h thng kiu ni tip, nh u vo khng c qu nhiu nhiu (nhm gim bt gnh nng x l tnh ton), c vy mi gii quyt c vn chi ph ng thi vn m bo tin cy. n ny s thc hin nhn dng vn tay bng nh s theo hng c th trin khai trong dn s. Chnh v vy phng php nhn dng l da trn c s pht hin v s dng cc im nt c trng (gi l minutiae) [2]. y l 1
1. GII THIU phng php th hai trong ba phng php nhn dng c p dng nhiu hin nay [1], ch. 4. H thng AFIS ni chung cng s dng phng php ny [11]. Phng php th nht, s dng c trng tng quan ca hai mu vn tay. Xp chng trc tip hai mu ny v da vo tng quan gia cc pixel tnh ton s khc nhau gia hai mu. Phng php ny khng thch hp vi n v i hi khi lng tnh ton ln m cht lng nh phi m tt. Phng php th ba, s dng cc c trng v ng vn. ng vn ca cc mu c trch ra khi nh ban u ri so snh gia chng. Phng php ny khng thch hp vi n v n ch thch hp vi cc mu c cht lng xu (chng hn nh vn tay ti phm li hin trng sau v n). n s s dng b mu chun cc vn tay c chun b trc. l cc nh s vn tay ly trong FVC200 (mt b d liu chun quc t xy dng bi phng th nghim h thng sinh trc, i hc Bologna). Trong tm ca n tp trung vo hai phn: To vec-t c tnh cho mc ch phn loi kiu vn tay v cho i snh vn tay (feature extraction). S dng cc im minutea trch chn bc trc i snh nhn dng vn tay (minutiae matching). n trnh by theo cu trc: Chng 1: Gii thiu chung. Chng 2: Vn tay trong sinh trc hc. cp mt s b phn ca sinh trc hc (trong c nhn dng vn tay) v nhng tnh cht g quyt nh vn tay c ng dng nhiu nht trong sinh trc hc. Chng 3: i cng v nh v x l nh trong Matlab, trnh by khi qut v nh s v mt s thut ton x l nh trong Matlab s dng trong n.
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1. GII THIU Chng 4: S khi thit k h thng. cp mt s m hnh h thng nhn dng vn tay v xy dng s khi h thng nhn dng vn tay bng nh s. Chng 5: B d liu nh s dng trong n. y l b d liu nh vn tay trch ra t FVC2000 (c s d liu nh vn tay chun, hin nay c nhiu nh khoa hc chn nghin cu v kim nghim kt qu). Chng 6: Trch chn c tnh vn tay v i snh vn tay. y mt trong nhng cng on quan trng nht ca n. Giai on ny p dng cc thut ton x l nh to m vn tay. Chng 7: i snh vn tay. Mu vn tay c to m t minutiae cng on trc c i snh trong cng on ny. Chng 8: Phn loi kiu vn tay. Trnh by v vn to vec-t c tnh cho khu phn loi kiu vn tay v thc hin phn loi kiu vn tay. Chng 9: Tng kt v hng pht trin. Trnh by nhng kt qu ca n, nhng kin thc bn thn thu c, cc hn ch v hng pht trin ti. Ti liu tham kho. Lit k mt s ti liu dng tham kho chnh trong n. Ph lc. Bao gm danh sch cc script file ca phn mm m phng v cc bc thc hin chy phn mm m phng nhn dng vn tay.
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2. VN TAY TRONG SINH TRC HC
2. Vn tay trong sinh trc hcTrong phn ny s trnh by nhng tip cn khi u, nh: v tr ca nhn dng vn tay trong sinh trc hc; nhng tnh cht ca vn tay tr thnh i tng c bn ca sinh trc hc; hnh thc th hin v c t ca mt mu vn tay v nhng kh khn gp phi khi nhn dng vn tay.
a)
b)
c)
Hnh-1. Mt s tn hiu sinh trc hc c bn: a) ging ni; b) ng t; c) ch k.
2.1. V tr ca nhn dng vn tay trong sinh trc hc Da vo tiu chun physiological sinh trc hc c: dng vn tay, mt, ng t, ging ni Cn da vo tiu chun behavioral sinh trc hc c: nhn dng ch vit, ch k Di y l biu tng quan ng dng sinh trc (s liu thng k ca International Biometric Group, 2002).
Hnh-2. ng gp ca cc ngnh trong sinh trc hc. (vn tay ng v tr hng u trong cc ng dng nhn dng)
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2. VN TAY TRONG SINH TRC HC 2.2. Uniqe l mt thuc tnh ca vn tay Cho ti nay, vn cha c bng chng xc thc 100% vn tay trn cc ngn tay tuyt i mang tnh c nhn v khng h lp li. Cu tr li chnh xc ch c c khi em so snh tng mu vn tay ca mi u ngn ngi vi hn su t ngi cn li. Tuy nhin khi khng xt ti phn nh l y c th rt ra mt s tnh cht c bn ca vn tay n tr thnh ph bin trong ng dng nhn dng v nh danh con ngi [2, 11]: Tnh ph thng, mi ngi u c. Tnh c nhn v khng lp li. Xc sut trng khp vi ngi khc gn bng khng. Tnh bt bin. Hnh dng tng th ca vn tay trn cc ngn tay ca con ngi khng thay i theo thi gian. Ngay c trng hp b chn thong nh, du vn tay vn c kh nng khi phc li. 2.3. Hnh thc th hin v cc c t ca vn tay Nhm mc ch m t ngi ta nh ngha mt s hnh thc th hin vn tay. Mi mt trng hp th hin th s c hnh thc trch chn c t vn tay tng ng. V vy, cn c vo nh vn tay u vo chng ta c th la chn c c tnh cn trch chn v d kin phng n nhn dng.
Hnh-3. Vn tay th hin cp very-fine: cc sweat pores c khoanh trn, im vn ch ba (bifurcation) v vn ct (termination) nh du hnh trn.
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2. VN TAY TRONG SINH TRC HC Hnh thc th hin vn tay c chia thnh ba cp : global (th hin tng th vn tay), local (th hin vn tay bi mt s nt c trng khi ng vn lm mnh n mt pixel), very-fine (th hin bi cc vng xuyn to hnh nn ng vn - sweat pores) [1], tr. 28-31, 83-85. i vi cp very-fine th i hi cc phng tin x l tn km cng nh cc yu cu c bit khc m kh c th ng dng trong dn s. Chng hn trch c cc pores, nh cn c phn gii ti thiu 1000dpi. Sau y s tm hiu su hn cc c trng vn tay hai cp u.
a)
b)
c)
d)
e)
Hnh-4. Vn tay th hin trong cp global: a) arch; b) whorl; c) tented arch; d) left loop; e) right loop; hnh vung nh du im loop, hnh tam gic nh du im delta.
cp global, c trng vn tay lin quan nhiu n s to hnh ca ng vn v cc im k d (singular), chng bao gm: loop (ng vn to vng xoy h), delta (ng vn to hnh tam gic). im k d c vai tr quan trng trong vic thc hin phn loi vn tay v t chc, xy dng c s d liu.
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2. VN TAY TRONG SINH TRC HC mc cc b, cc c trng ca vn tay c gi l minutiae. Ngi ta thng k c ti 150 c trng loi ny. Hai c trng c bn v ni tri hn c l ride temination v ridge bifurcation (cng c gi tt l minutiae)
a)
b)
Hnh-5. Hai dng minutiae quan trng: a) ridge termination; b) ridge bifurcation.
2.4. Kh khn gp phi khi nhn dng vn tay Do iu kin thu nhn nh quyt nh nhiu n cht lng nh thu thp nn nhiu khi cc chi tit trn mu vn tay khng th hin r rng. C th lit k mt s trng hp di y: Dry finger (vn tay thu nhn trong iu kin kh): nh thu nhn s c nhiu ch ng vn b m i, ng vn b ln vi nn nh. Lc n ca tay nh hoc mc in khng (vi vn tay ln trn giy) l cc nguyn nhn chnh lm gim cht lng nh thu thp. Wet finger (vn tay thu nhn trong iu kin t): nh thu nhn s c nhiu ch ng vn b dnh lin. Lc n ca ngn tay qu ln hoc mc in qu nhiu (vi vn tay ln trn giy) l cc nguyn nhn chnh to nhiu trong trng hp ny. Vn tay thu nhn trong iu kin b bin dng: nh thu nhn c c th th hin r nt nhng cc ng vn li b bp mo khng cn ging vi mu thc. Lc n, ko v x dch tay l cc nguyn nhn chnh. Vn tay thu thp khng y : nh thu thp c ch c mt phn vn tay trn ngn tay. Nguyn nhn chnh l do ngn tay t khng ng v tr chun thu thp. Tuy vy trong thc t cng c nhiu mu vn tay thu thp trong iu kin tt nn c cht lng cao 7
3. I CNG V NH V X L NH
3. i cng v nh s v x l nh trong Matlab n ny khng xy dng b thu thp mu vn tay m s dng b mu chun quc t FVC2000 do phng th nghim h thng sinh trc, i hc Bologna to ra. Trong c s d liu y, cc mu c lu d di dng nh s. Bi vy, qu trnh x l tnh ton thc hin n phi lm vic chnh vi dng s liu . Cho nn, trong phn ny s trnh by tm tt v nh s v mt s thut ton x l nh s trong Matlab. 3.1. i cng v nh s nh c th biu din di dng tn hiu tng t hoc s. Trong phn s tp trung vo biu din nh s, c s v mu v vic chuyn i mu.3.1.1. Biu din nh s
nh xm cng nh cc nh s khc l tp hp cc phn t nh hay cn gi l cc pixel, [i, j ] . nh c biu din nh mt ma-trn hai chiu c W H , hai thng s ny cho bit thng tin v rng v chiu cao nh. Gi tr ca mi phn t ca ma-trn I [i, j ] biu din cho mc xm hay cng nh ti v tr ca phn t .
f(1,1) f(1,2) L f(1,N) f(2,1) f(2,2) L f(2,N) f= M M M f(M,1) f(M,2) L f(M,N)
a) b) ma-trn biu din nh s
b)
Hnh-6. Biu din nh s: a) h trc ta trong Image Processing Toolbox;
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3. I CNG V NH V X L NH Ty theo yu cu lu tr, cc pixel s c m ha bng 8-bit, 16-bit, tng ng vi nh xm 256, 65536 mc. Vi nh en trng, cc pixel ny c lu tr bng 1-bit. Cng nh I ch c th l mt trong hai gi tr, I [i, j ] [0,1] . ng vi gi tr 0 l cc im en, cn vi gi tr 1 l im trng. Vi nh mu, cch biu din cng tng t nh vi nh xm, ch khc l cc gi tr ti mi phn t ca ma-trn biu din ba mu ring bit gm: (Red-R), lc (Green-G) v lam (Blue-B). biu din cho ba mu ring r cn 24-bit, 24bit ny c chia thnh ba khong 8-bit. Mi khong ny biu din cho cng sng ca mt trong cc mu chnh.3.1.2. C s v mu
nh sng mu l t hp cc nh sng n sc. Mt ngi c th cm nhn c mt s mu nht nh nhng li c th phn bit c rt nhiu mu (trong vng quang nhn thy, c di bc sng 400nm 750nm ). Cm nhn mu ca con ngi ph thuc vo ba thuc tnh B, H, S. B (brightness): chi, H (hue): sc lng, S (saturation): bo ha.
Hnh-7. Cm nhn ca cc t bo nhy sng trong vng mc mt vi cc mu nh sng ph thuc vo chiu di bc sng nh sng.
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3. I CNG V NH V X L NH Trong vng mc mt ngi c cc t bo cm th hnh nn nhy vi nh sng. C khong 6 7 triu t bo loi ny trong mt, chng chia lm ba nhm nhy vi ba mu nh sng khc nhau: 65% t bo nhy vi nh sng (red), 32% t bo nhy vi nh sng xanh lc (green) v 2% cn li nhy vi nh sng xanh l (blue). T hp B, H, S i vi tng nh sng mu trong ba mu ny gip mt con ngi c th phn bit c hng ngn mu. R, G, B cn c gi l cc mu c s. Phn b ph nng lng ca mt ngun sng mu c bc sng l k hiu l C (l ) v vic t hp mu theo ba mu c s (c cc ng cong cm nhn S1 , S 2 , S3 ) m t bng s khi sau:
Hnh-8. T hp mu.
p ng ph a i ( C ) s c tnh nh sau trong di bc sng
ai ( C ) =
lmax lmin
Si (l )c(l )d l , i = 1,3 .
Vi phn phi xc xut ca ba mu pk ( x ) , k = 1,3 nn c:x max
x min
pk ( x)dx = 1 .
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3. I CNG V NH V X L NH Gi s ba mu c bn c t hp theo t l b k ( l ) , i = 1,3 . to ra mt mu c phn b ph nng lng C ( l ) s bng
bk =1
3
k
(l ) pk ( x) .
Thay gi tr vo phng trnh v p ng ph:3 3 3 a i (c ) = Si (l ) b k ( x ) pk ( x ) dx = b k ( x) Si (l ) pk ( x )dx = b k ( x )ai ,k k =1 k =1 k =1 l min l min
l max
l max
trong : a i, k =
l max
l min
Si (l ) pk ( x )dx .
Nh vy c th t hp mu theo php cng mu vi a i l h s t hp theo cng thc tng qut sau: X = a 1 R + a 2G + a 3 B
T chc quc t v chn ha mu CIE a ra mt s khng gian mu nh: RGB, CMY, CMYK, HIS, Trong m hnh RGB c vai tr quan trng.
red Px = green blue
a)
b) Hnh-9. H ta mu: a) m hnh mu RGB; b) biu din im nh trong h ta mu RGB.
11
3. I CNG V NH V X L NH3.1.3. Chuyn i mu
H ta mu do CIE quy nh nh mt h quy chiu v trn thc t khng th biu din ht cc mu. Ty thuc vo cc ng dng khc nhau ngi ta a ra thm mt s h ta khc nh NTSC, CMY, YIQ... ph hp vi yu cu hin th mu sc. Vic chuyn i gia cc khng gian biu din mu thc hin theo nguyn tc sau:Px = A Px* ,
trong :Px : khng gian biu din mu ban u, Px* : khng gian biu din mu mi, A : ma-trn php bin i.
nh dng trong n ny l nh xm. Mc xm l kt qu ca s m ha tng ng mt cng sng ca im nh vi mt tr s. Gi tr ca n ph thuc vo mc lng t ha nh, nh cc nh dng lm c s d liu ly 8-bit m ha nh (ng vi 256 mc xm, trong mc xm 0 l mu en, mc xm 255 l mu trng). Khi chuyn i t nh mu RGB sang nh xm c th dng cng thc sau:grayscale = a1 R + a 2G + a3 B ,
cc h s ai ln lt nh di y [6].a1 = 0, 2989; a 2 = 0,5870; a 3 = 0,1140
12
3. I CNG V NH V X L NH 3.2. X l nh s trong Matlab ng v mt x l tn hiu ni chung v x l nh ni ring, Matlab l cng c rt mnh. Hu ht cc thut ton v nh v x l nh u c th hin trong cc hm ca Matlab nh cc hm c, ghi nh, chuyn i gia cc h mu ca nh, cc thut ton pht hin bin, tch i tng, khp mu, cc php bin i nh nh xoay nh, chun kch thc, tnh tin,... Cc th vin ngy cng c m rng, cc hm ng dng c th c lp bi ngi s dng. ng dng phn mm Matlab trong x l nh s c c nhiu tin ch v tr gip. Cu lnh Matlab c gn vi cc thut ng m t k thut, cu lnh ngn gn v c th tra cu nhanh trong chc nng Help. Trong Matlab c nhiu Toolbox h tr cc ng dng chuyn su. Vi bi ton nhn dng hnh nh, cc Toolbox thng c s dng gm: Image Processing Toolbox Image Acqusition Toolbox Wavelet Toolbox Signal Processing Statistics Toolbox Neural Network Toobox Cc thut ton x l trong n u c vit bng ngn ng lp trnh phn mm Matlab. Cc chng trnh c s dng mt mt s th vin ca Matlab (ch yu trong Image Processing Toolbox, Statistics Toolbox). Sau y l mt s cng c x l v thut ton x l nh chnh c ng dng trong n.3.2.1. Histogram
Histogram (lc xm) th hin tn sut xut hin mi mc xm trong nh. Lc xm biu din trong h ta Oxy: trc honh biu din N mc xm (ty theo s bit m ha pixel), trc tung biu din s im nh mt mc xm tng ng.
13
3. I CNG V NH V X L NH Lc xm cung cp thng tin v phn b mc xm ca nh. N cho php phn tch trong khong no phn b phn ln mc xm ca nh. Nu nh sng th lc xm lch v pha bn tri, nu nh ti th lc xm lch v bn phi so vi im quy chiu (gia mc xm N).
a)
b)
c) c) nh ti v d) lc xm ca (c) lch tri.
d)
Hnh-10. Phn tch lc xm: a) nh sng v b) lc xm ca (a) lch phi;
3.2.2. Phn ngng cc b
Phn ngng vi mc ch lm tng tng phn cc i tng cn quan tm ng thi loi bt nhiu. Nu phn ngng ton b nh nhiu khi t ra khng hiu qu, nht l khi cng sng ca nh khng ng u. Phn ngng cc b cng ging nh phn ngng nhng ch khc im: ngng c chn thch nghi vi tng vng cc b ca nh. iu ny rt c ngha trong khu nh phn ha nh vn tay. Vng cc b thng dng c th l cc block dng hnh vung hay hnh ch nht.
14
3. I CNG V NH V X L NH nh xm khi phn ngng th kt qu phn ngng i i vi nh phn ha nh. Mt im bt k (x, y) thuc nh f khi c f ( x, y ) T th c gi l object point (im trn nn), trng hp cn li gi l background point (im nn). i tng u tin trch chn t phn ngng khng quan trng l bachground point hay object point. y ch l cc tn gi quy c v chng c th chuyn i d dng cho nhau nh bin i m bn.
Hnh-11. Gi tr ngng ti u.
Kt qu phn ngng c nh g ( x, y ) th n c nh ngha lin h
1 : f ( x, y ) T g ( x, y ) = 0 : f ( x , y ) < T
3.2.3. Bin i Fourier-2D ri rc
Bin i Fourier ri rc trong x l nh s nhm mc ch lc ly cc thnh phn tn hiu nh c tn s tri. Vi nh vn tay vng nh co cc ng vn ng vai tr lm tn hiu c tn s tri. C f ( x, y ) , vi x = 0, M - 1 v y = 0, N - 1 l mt nh s c M N . Bin i Fourier ri rc ca f l F (u , v) .
F (u, v) = f ( x, y )e - j 2p ( ux / M + vy / N ) , u = 0, M - 1 , v = 0, N - 1 .x =0 y =0
M -1 N -1
15
3. I CNG V NH V X L NH Bin i ngc Fourier ri rc nh ngha bi cng thc:M -1 N -1 u =0 v =0
f ( x, y ) = F (u , v)e -
j 2p ( ux / M + vy / N )
, x = 0, M - 1 , y = 0, N - 1 .
Bin i Fourier ri rc ca nh f cn c vit di dng:F (u, v) = F (u, v ) e - jf ( u ,v ) ,
trong f ( u, v ) l gc pha, F (u, v ) l ph Fourier. Cc bc thc hin lc nh trong min tn s bng bin i Fourier ri rc c th m t bi s di y.
Hnh-12. Cc bc thc hin lc nh trong min tn s.
3.2.4. Lc nh Sobel
Lc Sobel l mt trng hp ca lc s tuyn tnh. Ngha l b lc dng mt convolution-mask (ca s dng nhn chp, gi tt mask), ri ly tng c trng s cc im ln cn vi im chnh gia trong mask . Di chuyn mask trn ton b min tn hiu nh, mi bc mt pixel, cui cng thu nh kt qu. 16
3. I CNG V NH V X L NH Tng qut, lc tuyn tnh ca nh s f c M N vi convolution-mask c cm n nh bi nh sau
g ( x, y ) =
s =- a t =- b
w ( s , t ) f ( x + s, y + t ) ,
a
b
trong : a = ( m - 1) / 2 , b = ( n - 1) / 2 v x = 0, M - 1 , y = 0, N - 1 .
Hnh-13. Cc bc lc nh bng ton t khng gian.
17
3. I CNG V NH V X L NH p ng lc s ti tng im (x,y) l R, i vi lc Sobel s lRx = wxi zi = ( z7 + 2 z8 + z9 ) - ( z1 + 2 z3 + z4 ) ,i =1 9 9
Ry = wyi zi = ( z3 + 2 z6 + z9 ) - ( z1 + 2 z 4 + z7 ) ,i =1
trong zi l mc xm ca nh.
a)
b) b) cc h s ca cp mask dng cho lc Sobel
Hnh-14. Biu din mask: a) cc h s ca mask c 3 3 ;
3.2.5. Pht hin bin bng ton t gradient
S dng ton t gradient trong min 2D l mt trong cc phng php dng pht hin bin. Ton t nh ngha nh l mt vec-t hai thnh phnGx f x f = = G y f y
Ton t xc nh m-un v gc ca gradient ln lt nh sau2 f = mag ( f ) = Gx2 + G y 1/ 2
a ( x, y ) = arctg ( Gx G y ) .
2 2 = ( f / x ) + ( f / y )
1/ 2
,
18
3. I CNG V NH V X L NH Thng thng thnh phn m-un ch cn tnh xp x l t yu cu chnh xc ca bi ton t ra. Hai cng thc gn ng hay s dng l tng cc bnh phng f Gx2 + G y2 v tng cc gi tr tuyt i f Gx + G y .
19
3. I CNG V NH V X L NH3.2.6. Loang rng v thu nh i tng
Loang rng (dilation) v thu nh (erosion) i tng l hai ton t c ca nhm thut ton x l morphology. C hai ton t ny ch p dng cho cc nh nh phn v m t ton hc ca morphology l cc php ton tp hp [3]. n s vn dng nhiu hai thut ton trong cng on: khoanh vng nh, lm mnh bin, v hiu chnh ng vn.
a)
c)
b)
d)
Hnh-15. Loang rng i tng. a) nh ban u vi i tng hnh ch nht; b) strel c ba pixel xp thnh dng on thng, cho 450 so vi phng ngang; c) strel di chuyn khp nh v cc im b tc ng; d) nh kt qu.
Phn t c bn thc hin loang rng hay thu hp gi l structuring element (vit tt l strel). Cn c vo nh gc cng vi ln v hnh dng ca 20
3. I CNG V NH V X L NH strel, i tng b ct bt hoc thm vo tng im nh (ph hp vi khun hnh ca strel) Trng hp c bit, p dng ton t thu hp lin tip s ln th c qu trnh lm mnh i tng ti mt pixel.
a)
c)
b)
d)
Hnh-16. Thu nh i tng. a) nh ban u vi i tng hnh ch nht; b) strel c ba pixel xp thnh dng on thng vung gc vi phng ngang; c) strel di chuyn khp nh v cc im bi tc ng; d) nh kt qu.
21
4. THIT K S KHI H THNG
4. S khi thit k h thng nhn dng vn tayTrong phn nay s gii thiu mt s phng php nhn dng vn tay. Tip theo l cc hnh h thng nhn dng a nng. mi phn, s la chn ra phng n thc hin trong n. y l hai tin xy dng nn s h thng nhn dng vn tay cho n ny. 4.1. Cc nguyn l nhn dng vn tay Cc nguyn l nhn dng vn tay th lin quan cht ch n cch thc tm ra s tng ng gia nh vn tay u vo vi mt template trong c s d liu vn tay. Di y l ba phng php chnh ln lt da trn cc c s l i snh minutiae, correlation v ridge feature [1], ch. 4. Minutiae-base matching, Correlation-base matching, Ridge feature-base matching.
a) (cc minutie c nh du O)
b)
Hnh-17. To m vn tay: a) nh ban u; b) trch chn minutiae quan trng
22
4. THIT K S KHI H THNG Phng php u tin ph bin hn c v c ng dng rt rng ri. Hai vn tay s c so snh bng cc im minutiae trch ra t cc vn tay . Giai on th nht ny cn goi l to m [11], cc minutiae to thnh tp hp im c trng v c lu tr trong tng mng 2D. Giai on th hai s tm v tr khp ph hp gia template v input-image sao cho s cc minutiae tao thanh cp tng ng l ln nht. Cn hai nguyn l cn li khng ph hp vi n. Correlation-based thc hin bng cch xp chng hai mu vn tay ln nhau tm ra tng quan gia chng, phng php ny gp hn ch khi qu trnh thu nhn nh vn tay gp phi cc bin dng mo. Cn ridge feature-base l mt phng php cao cp, i hi cc bc x l phc tp v thng dng cho ng dng nhn dng vi cc vn tay c cht lng rt xu (chng hn nh vn tay latent). n ny la chn phng n u tin v l mt phng php c bn, ph hp vi iu kin hin ti cho php v cng ha hn cho kt qu kh quan. 4.2. H thng nhn dng vn tay Nhn dng vn tay l mt b phn ca sinh trc hc. V th phn loi h thng nhn dng sinh trc hc cng bao hm cho h thng nhn dng vn tay ni ring. C hai hnh thc phn loi h thng nhn dng vn tay: da trn kin trc ca h thng v cch x l d liu trong h thng [1], tr. 237-240. a) Phn loi h thng theo kin trc: H thng c kin trc song song H thng c kin trc ni tip H thng c kin trc th bc b) Phn loi h thng theo cc x l d liu: H thng c khu hp nht sau trch chn c tnh H thng c khu hp nht sau i snh H thng c khu hp nht sau tng hp kt qu Vi khun kh n, s chn h thng cu trc ni tip lm nn tng. 23
4. THIT K S KHI H THNG 4.3. Xy dng h thng nhn dng vn tay bng nh s Trn c s cc phn tch nu, sau y l xut v s khi h thng nhn dng vn tay bng nh s. H thng ny c kh nng phn loi vn tay, to c s d liu v nhn dng vn tay. Kiu nhn dng l identification, ngha l mt mu cn nhn dng (input) s nhn kt qu bng cch i snh vi N mu khc trong c s d liu (template). Kiu ch hot ng ca h thng hng n l online. Ngha l h thng c th hot ng lin tc, c kh nng ghp vi khu thu thp s liu s cc phng php thu nhn nh live-scan (bng my scan, sensor,) v quan trng hn c th va thu thp s liu va c th nhn dng. Kin trc h thng thit k theo hng x l d liu ni tip, gm tm khu chnh trnh by trong Hnh-18.
Hnh-18. S khi h thng nhn dng vn tay.
Tm khu ny c c chc nng hot ng nh sau: 1) Khu s 1: thc hin thu nhn nh.
24
4. THIT K S KHI H THNG 2) Khu s 2: thc hin trch chn c tnh vn tay phn loi. c tnh trch chn l gc nh hng, orientation. 3) Khu s 3: thc hin to vec-t c tnh phn loi. 4) Khu s 4: thc hin phn loi vn tay lm nm nhm. 5) Khu s 5: lm c s d liu, lu tr cc template-image. 6) Khu s 6: thc hin trch chn minutiae. c tnh trch chn l miutiae. 7) Khu s 7: thc hin i snh input-image vi template-image. 8) Khu s 8: thc hin a ra kt qu nhn dng.
25
5. TP MU NH VN TAY
5. Tp mu nh vn tayVn tay c th lu tr theo hai cch: trn giy (giy thng, giy nh...) hoc file nh. i vi cch th nht vn cn c ng dng trong gim nh, nh danh hnh s (cc bng chng v du tay ti phm cn c th hin bng nh in trn giy). Cch th hai c ng dng ph bin trong nhn dng ni chung v ngy cng chim c nhiu u th (c th lu tr, tm kim thun tin). n ny tp trung n hnh thc lu tr nh theo file.
a)
b)
c)
Hnh-19. Cc loi vn tay: a) vn tay latent; b) vn tay ln mc; c) vn tay trong Db2b-FVC2000.
C nhiu nh dng nh vn tay khc nhau, ph bin hn c l: jpeg, bmp, tif, gif, png,... Cc thng s nh bao gm: rng ca nh, phn gii, s bit dnh cho mt pixel, chnh xc hnh hc, mo,... Khi thit k h thng nhn dng vn tay, cc thng s nh thng thng c quy chun theo gii gi tr no sao cho ph hp vi h thng. H thng nhn dng vn tay bng nh s, nh s l i lng u vo nn hai thng quan tm hn c: kch thc v phn gii. Nh trnh by trn, n ny s dng d liu nh FVC2000 to c s d liu h thng nhn dng v kim tra kt qu nhn dng. Cc mu vn tay lu theo file nh, c phn m rng .tif, kch thc ca nh 364 256 pixel. Mi mu vn tay gm by nh khc nhau v c lu tn theo quy c xx_y. Trong xx l ch s v th t ca b mu (cn gi l ch bn) trong tp d liu nh, y l th 26
5. TP MU NH VN TAY t ca nh trong mt b mu. B mu s c chia lm hai: mt phn dng thc hin trch chn v to m cho vn tay thng qua cc thut ton x l nh (mc ch cui l to ra cc template xy dng c s d liu); phn cn li dng kim tra, nh gi thut ton x l.
27
6. TRCH CHN MINUTIAE
6. Trch chn minutiae cho i snh vn tay n ny c thit k bng cch chia nh cc cng on chnh trn thnh cc m-un nh hn. Hng chung l chn cc phng php m c th tn dng c cc m-un chng trnh cng on ny v p dng c cho cng on khc. Nhng cc phng php la chn phi t yu cu cho bi ton nhn dng cui cng. V vy, to tnh m cho h thng v tit kim thi gian thit k.
Hnh-20. Thut ton trch chn minutiae.
Vi s ny thy rng, trch chn minutiae thc hin qua tm khu. Khi tin x l nh thc hin chun ha kch thc nh. Khi tng cng cht lng nh thc hin lm ni r ng vn. Khi orientation image thc hin c lng trng nh hng. Khi segmentation (khoanh vng nh vn tay) thc hin tch vng nh cn quan tm nhiu trong x l trch chn c tnh. Khi to ridge map (nh nh phn vi ng vn c gi tr logic 1). Khi lm mnh ng vn. ng vn lm mnh ti rng ng nht mt pixel t ridge map. Khi hiu chnh ng vn v lc minutiae sai cp mt. ng vn s c lm trn, minutiae sai kiu lake (dng hnh xuyn nh), dng im, ch ngn, on vn ngn s loi b. Lc minutiae sai cp hai v to m vn tay bng minutiae. Kt thc khu ny cc template s c to ra. 28
6. TRCH CHN MINUTIAE 6.1. Chun ha nh u vo Chun ha nh u vo l bc cn thit trc khi vo bc tin x l nh. Do nh dng cho trch trn c tnh c th khng ph hp v kch thc cng nh phn b mc xm. Trong n, giai on ny gm: chun ha kch thc nh v ng u ha cng sng gia cc nh u vo khc nhau.6.1.1. Chun ha kch thc nh
nh chun u vo c kch thc 364 256 pixel. Cc thut ton x l nh vn tay v sau thng p dng cho tng tng block vung trn nh (thng s dng cc block vung cnh 16 pixel, 32 pixel,). Nn kch thc nh chun ha hp l hn l 352 256 pixel. thc hin iu ny s ct i vng d liu nh kch thc 12 256 pixel. Phn ny cng khng nh hng qu nhiu ti kt qu nhn dng cui cng v i vi b d liu chn, cc vng nh gn khung thng ng vai tr lm background. Hm thc hin chun ha kch thc nh u vo l norsizfv. gns = norsizfv(g, bs), trong : g bs : nh s u vo c kch thc cn c chun ha, : kch thc ca block m nh u ra s c lm trn theo,
gns : nh u ra c kch thc chun ha.
6.1.2. Cn bng cng sng ca nh
Do iu kin thu thp nh khc nhau vi mi ln ly mu vn tay; do k thut thu nhn nh (s dng sensor, scanner,) khc nhau nn sng nh vn tay khng gn nht. V vy cn lm ng u cng sng ca cc nh vn tay trong b d liu. Phng php thc hin: dng mt nh mu c cng sng ng u, ri chun ha sng ca cc nh khc theo nh ny bng bnh phng cc tiu. Trong n s dng nh c cng kch thc cng snh cc im nh I [i, j ] = 128 (l mc xm trung trung bnh trong 255 mc). 29
6. TRCH CHN MINUTIAE Hm thc hin cn bng cng sng ca nh l briequfv. gbb = briequfv(g,ref), trong : g : nh s u vo cn c chun ha cng sng, ref : nh s lm mu gbb : nh u ra c cng sng gn vi nh mu.
6.2. Tng cng nh cht lng nh Thu nhn nh khng phi lc no cng cho nhng nh vi cht lng tt. Tng cng nh s gip ci thin cht lng nh trc khi thc hin cc thut ton x l nh tip theo nhm gia tng hiu qu x l. Hai thut ton s dng tng cng nh cht lng nh y l: histogram equalization (cn bng lc xm) v bin i Fourier ri rc [1], tr. 104-113.
a)
b) c) nh sau bin i Fourier ri rc.
c)
Hnh-21. Tng cng nh: a) nh ban u; b) nh sau cn bng histogram;
6.2.1. Tng cng nh bng cn bng histogram
Histogram ca nh xm l mt biu th hin quan h gia cng nh v s pixel c cng cng cng nh . Cn bng histogram s lm ng u cng sng trong bn thn nh . 30
6. TRCH CHN MINUTIAE Hm thc hin tng cng nh bng cn bng lc xm l hisequfv. ghe = hisequfv(g), trong : g ghe : nh s u vo, : nh u ra c tng cng bng cn bng lc xm.
6.2.2. Tng cng nh bng bin i Fourier-2D
S dng lc Gabor v bin i Fourier l hai nn tng chnh thc hin tng cng nh trong x l nh vn tay. nh sau khi c tng cng cht lng bng histogram equalization, thc hin bc k tip l tng cng nh bng thut ton bin i Fourier [1, 8, 9, 10]. So vi cc phng php trn c s lc Gabor, n li th hn ch khng yu cu vic tnh ton chnh xc nh hng cc b ca ng vn v tn s vn tay phc v cho mc ch cui cng on to ridge-map. Cng thc tnh ton cho thut ton tng cng nh bng bin i Fourier ri rc c dng nh sau:I enh = F -1{F (I [ x, y ]) F (I [ x, y ]) }k
trong : kF ( I [ x,y ])
: h s m ca ph Fourier, : ph Fourier.
n thc hin tng cng cht lng nh bng bin i Fourier ri rc cho tng block c kch thc 32 32 pixel. Theo cch ny, cc thnh phn nh c tn s tri s c gi li, l cc vng nh th hin lm ng vn. nh sau bin i Fourier ri rc c cc ng vn ni hn, s phn tch gia cc ng vn cng th hin r rng hn. ng thi cc vng nh nhiu s loi bt i. 31
6. TRCH CHN MINUTIAE S m ca ph Fourier, k ng vai tr lm h s iu chnh. Trong [1], khuyn ngh t k = 0,6 khi tnh ton vi kch thc block nh trn. Tuy nhin, trong qu trnh thc hin, t k = 0, 35 th cho kt qu tt hn so vi vic chn gi tr khc. V ph Fourier ng vai tr lm hm lc, do : k cng nh hm lc tin ti 1 (nh gc v nh sau khi tng cng khng khc nhau nhiu); vi k ln, cc on vn cc b c th b bin dng khng cn kh nng x l cho cng on tip na. Hm thc hin tng cng nh bng bin i Fourier ri rc l fouenhfv. gfe = fouenhfv(g,k), trong : g k : nh s u vo, : h s,
gfe : nh u ra c tng cng bng bin i Fourier.
6.3. c lng orientation image v khoanh vng nh vn tay Trong phn ny s trnh by cc c lng nh hng vn tay cc b. y l cn thit chn c cc thng s thch hp lc nh v sau (lc nhiu, khoanh vng nh...). V orientation image (trng nh hng) mang tnh m t gc nh hng ng vn, nn kt qu ny cn c p dng phn loi kiu vn tay (quyt nh bi s to hnh ca cc ng vn).6.3.1. c lng orientation image
Trng nh hng th hin bn cht t nhin ca ng vn v cc rnh ng vn. Trng nh hng cung cp nhiu thng tin quan trong cho cc bc x l tip theo. Phn ny s trnh by v c lng orientation image D, phn t nh hng q ij (tng ng vi n l gc nh hng qij v m-un nh hng). C s phn bit khc nhau gia cc thut ng m t phn t nh hng orientation (c qij [ 0, p ] ), direction (c qij [ 0, 2p ] ) khi tnh ton trng nh hng [1].
32
6. TRCH CHN MINUTIAE Nguyn l thc hin tnh nh hng: chia nh thnh cc khi w w , sau kho st ln lt nh hng cc b ca ng vn trong tng khi . Orientation image s c c lng bng phng php Gradient [3, 4]
a) b) orientation image tng ng
b)
Hnh-22. c lng orientation image: a) nh vn tay ban u;
Cc cng thc tnh ton:w 2 w 2
Gn (i, j ) =
i+
2 g (u, v )g (u, v ) ,w w v= j 2 2 j+ x y i+
j+
u =i -
Gd (i, j ) =
(g (u, v ) - g (u, v )) ,w w v= j 2 2 2 x 2 y
w 2
w 2
u =i -
q ( i, j ) =
G ( i, j ) 1 arctg n . G ( i, j ) 2 d
y: g x (i, j ) , g y (i, j ) l cc gradient ti (i, j ) theo cc trc x, y v tnh bng ton t Sobel [5, 6].
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6. TRCH CHN MINUTIAE Hm thc hin c lng trng nh hng l oriimafv. [iD, iC, DF] = oriimafv(g,bs), trong : g bs iD iC DF : nh s u vo, : kch thc block vung c lng nh hng, : ma-trn lu nh hng ca mi block, : ma-trn lu level-certenty ca mi block, : ma-trn lu nh hng v ta tm ca mi block.
6.3.2. Khoanh vng nh vn tay
Khoanh vng nh vn tay nhm mc ch phn chia cc vng khc nhau trn nh vn tay. y, chng ta quan tm n foreground/background (nh nn v nh trn nn) cng vi bin nh vn tay. Trong nhn dng vn tay, vng nh mang thng tin hu ch gii hn bi vng c cc ng vn (ng vai tr lm foreground). Vng nh cn li thng l cc nhiu to ra trong qu trnh thu nhn, sao chp, lu tr nh (ng vai tr lm background) cn c tch ra khi foreground. Khoanh vng nh vn tay nm trong nhm thut ton segmentation. Tng qut, n da vo hai tnh cht ca nh s lin quan n cng sng thc hin, l: s khng lin tc v s tng t nhau [3]. nh vn tay trong n s khoanh vng ly vng hu ch da vo c hai tnh cht k trn. Tiu ch nh gi l certainty level (mt gi tr th hin s bin thin ca cng sng theo cc ng vn). Theo cch ny vng nh ng vai tr background v foreground c phn tch nh mt ngng t trc [2]. Cng thc tnh certainty level cho tng block kch thc w w , trng tm tng ng ca block c ta [i, j ] nh sau:
C (i, j ) =
1 Gn (i, j ) + Gd (i, j ) w w Gs (i, j )2
2
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6. TRCH CHN MINUTIAE Mt ngng Tc c t ra v block nh ngha lm background nu C (i, j ) < Tc , foreground nu C (i, j ) Tc . Phng php ny c li th k tha c cc kt qu tnh ton trong phn c lng orientation image.
a)
b) c) nh khoanh vng ng vn.
c)
Hnh-23. Khoanh vng nh vn tay: a) nh ban u; b) variance field;
Hm thc hin khoanh vng nh c cc ng vn tay l segimafv. area = segimafv(iC,k), trong : iC bs : ma-trn lu gi tr level-certenty cc b, : kch thc block,
area : vng nh vn tay c khoanh.
6.4. Trch chn minutiae Giai on ny bao gm: nh phn ha nh bng thut ton local threshold vi nh c tng cng kt hp vi kt qu khoanh vng nh vn tay phn
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6. TRCH CHN MINUTIAE trn; sau vi nh c cc ng vn c lm mnh n rng mt pixel th thc hin tm minutiae bng thut ton crossing number [1], ch. 4.
a)
b)
Hnh-24. Thng s ca hai dng minutiae quan trng: a) bifurcation; b) termination.
6.4.1. Nh phn ha v lm mnh ng vn
Sau tng cng nh bng bin i Fourier ri rc, ng vn ty ni r hn so vi nh ban u. y l lc s dng thut ton local threshold chuyn i nh xm tng cng cht lng thnh nh en trng.
a)
b)
Hnh-25. Nh phn ha v lm mnh ng vn: a) ridge-map; b) thinned ridge-map.
Kch thc ca s 32 32 pixel trong bin i Fourier ri rc th kch thc block cho phn ngng cc b c th l: 32 32 , 32 16 , 16 16 , 16 8 pixel Th nghim vi block 16 16 pixel th cho kt qu tt hn (cc ng vn tch bit r 36
6. TRCH CHN MINUTIAE rng hn). nh ny tip tc c lm mnh bng thut ton morphology cho nh en trng sau cng vi ng vn th hin bng ng mu trng (gi tr logic 1) c rng ng nht mt pixel. Hm thc hin nh phn ha nh vn tay l locthrfv. glt = locthrfv(g,bs,adj), trong : g bs adj glt : nh u vo, : kch thc block, : h s hiu chnh, : nh u ra c nh phn ha.
6.4.2. Pht hin minutiae
Vn tay sau khi lm mnh c th bt u tm cc minutiae. Thut ton dng pht hin minutiae s dng trong n l crossing number. N dng mt ca s kch thc 3 3 pixel, ly tt c cc im nh trong ca s, sau kho st gi tr logic ca cc im nh xung quanh im nh [i, j ] chnh gia ca s . Ty vo kt qu tnh ton ca biu thc crossing number th kt lun rng: im
[i, j ] ang xt l mt im phn nhnh, im ct hay ang nm trn mt ngvn. Cng thc tnh nh sau:1 8 val ( pi mod 8 )- val ( p i-1 ) 2 i =1
cn( p) =
nh s dng pht hin cc minutiae phi l nh nh phn, do val ( p ) {0, 1} . Cc bin p1 , p2 , ..., p7 th t to thnh cc im ln cn im gia ca s ang kho st xt theo mt chiu thun hoc ngc kim ng h.
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6. TRCH CHN MINUTIAE Khi nh ngha im [i, j ] ang xt l: trn ng vn nu cp(n) = 2, termination minutiae nu cn(p) = 1, bifurcation minutiae nu cn(p) = 3. Thut ton tm kim v gi tr crossing number c vai tr quan trng. Khng nhng c dng trong vic pht hin minutiae m n cn gip loi b cc minutiae sai (c cho l nhiu).
a) cn(p) = 2
b) cn(p) = 2
a) cp(n) = 3 d) termination minutiae.
d) cn(p) = 1
Hnh-26. Pht hin minutiae: a), b) pixel trn ng vn; c) bifurcation minutiae;
Hm thc hin pht hin minutiae l finminfv. [ter, bif] = finminfv(g), trong : g ter bif : nh u vo c rng ng vn mt pixel, : ma-trn lu ta ca termination minutia, : ma-trn lu ta ca bifurcation minutia. 38
6. TRCH CHN MINUTIAE6.4.3. c lng khong cch ng vn
Vn tay trn ngn tay khng ging nhau gia mi ngi. Ngay c trng hp mt ngi, cc ng vn cng th hin s khc bit trn tng ngn tay. Do vy, c lng khong cc ng vn c hiu l di tr trung bnh khong cch gia hai ng vn song song v gn nhau. y l mt thng tin lm tin cho cng on lc minutiae v sau. nh nh phn c cc ng vn c lm mnh n 1 pixel to ra t khu lm mnh c, t ra rt thun tin vi phng php scan trong vic c lng khong cch ng vn. Theo cch ny, s qut mt s dng v mt s ct trn nh (thinned ridgemap), lu li v tr im trn ng vn, sau tnh gi tr trung bnh khong cch im l c kt qu cn tm. Hm thc hin pht hin c lng rng ng vn l mearidfv. rd = mearidfv(g), trong : g rd : nh u vo c rng ng vn mt pixel, : rng trung bnh ca ng vn.
6.4. Hiu chnh ng vn v lc minutiae sai Trong phn ny s trnh bay v vn vn loi b cc minutiae sai. Nhng nhiu ny ch yu c tao ra t qu trnh lm mnh ng vn, v cng c nhng nhiu t khu thu nhn nh Cc cng vic thc hin: lm trn ng vn, ni cc ng vn b t trong ngng gii hn, tch cc ng vn b dnh, cui cng l to m vn tay t minutiae.6.4.1. Hiu chnh ng vn v lc minutiae sai cp mt
Giai on ny thc hin hiu chnh cc vn tay v cc tn hiu cho l nhiu (on vn ngn, ch nhnh ct, vng xuyn nh) s c loi i. Nh vy s
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6. TRCH CHN MINUTIAE lm tng tnh xc thc ca cc minutiae trch chn c so vi nh vn tay gc ban u.
a)
c)
Hnh-27. S minutiae pht hin c: a) ngay sau lm mnh vn; b) sau lc minutiae. (vng nh nh du vung v trn th hin in hnh mt s minutiae sai c loi b)
Khi thc hin hai nhim v ny, thng tin cn cn bit trc l khong cc trung bnh gia cc ng vn rd. N c c lng t bc scan nh vn tay lm mnh trnh by trn. Sau , vic lc minutiae s cn c theo rd cng thm cc im nt tm thy bng thut ton crossing number.
a)
b)
Hnh-28. Lc cc minutiae. a) minutiae sai; b) cc minutiae sai b loi b
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6. TRCH CHN MINUTIAE Hm thc hin pht hin thut ton hiu chnh ng vn tay v lc minutiae cp mt l smoridfv. [gs, ster, sbif] = smoridfv (g), trong : g gs : nh u vo c rng ng vn mt pixel, : nh u ra c lm trn ng vn,
ster : ma-trn lu ta ca termination minutia, sbif : ma-trn lu ta ca bifurcation minutia.
6.4.2. Lc minutiae sai cp hai v to m t minutiae
Khi cc ng vn lm trn, cc im minutiae c tm kim mt ln na v s lng cc im sai cng c gim ng k. Tuy nhin cn hai li m qu trnh trn cha khc phc c l ni cc ng vn b t (khong cc gia hai u mt < rd) v ct on vn ni hai ng vn dng cu ch H (khong cch cu < rd). Gii php thc khc phc l so snh khong cch nh gia hai im nt v gc nh hng ca chng theo ngng ( Dd , Dq ) loi b. Trong n chnDq [ - p 6, p 6] (khong gc rng hn hoc hp hn t ra t c hiu qu trong
khi thc hin n), cn Dd = rd .
Hnh-29. Cc minutiae c trch chn cui to m.
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6. TRCH CHN MINUTIAE Hm thc hin sai cp hai v to m t minutiae l extminfv [eter, ebif] = extminfv (g), trong : g : nh ng vn mt pixel lm trn. eter : ma-trn lu ta ca termination minutiae, ebif : ma-trn lu ta ca bifurcation minutiae. Cc minutiae trch chn cui cng ny s c lu tr thnh file to template cho c s d liu. Thng tin lu tr l ta , nh hng minutiae. Qu trnh to m t minutiae hon tt khu trch chn c tnh nh danh.
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7. PHN LOI VN TAY
7. Phn loi kiu vn tayH thng nhn dng identification, c s d liu c th ln n hng triu ch bn nn qu trnh i chiu 1:N d nhin tn rt nhiu thi gian [1], tr.173. Phn loi vn tay nhm mc ch t chc cc template theo tng category (nhm phn loi) tit kim thi gian nhn dng (cho mt input-image khi h thng hot ng).
a)
b)
c)
d)
e)
Hnh-30. Nm kiu vn tay trong thc t: a) arch ; b) whorl ; c) tented arch; d) left loop ; e) right loop.
Mc d n gii hn trong s lng mu t thc hin x l d liu v th nghim. Nhng h thng nhn dng vn tay trong n ny c thit k theo kiu identification (c kh nng i chiu 1:N). Tun th kiu nhn dng ca h thng v hng thit k m t ra ban u th phn loi vn tay l khu khng th b qua. Gii php phn loi vn tay y s dng cy quyt nh (treefit), nh vy s k tha c nhiu kt qu ca phn trch chn c tnh vn tay cho i chiu trn. 43
7. PHN LOI VN TAY Qu trnh phn loi vn tay c thc hin qua ba khu chnh 1) trch chn c tnh nh hng cc b, 2) to vec-t c tnh, 3) b phn loi. Cc vn tay c phn loi vo nm category: A, L, R, T, W, tng ng vi arch, left loop, right loop, tented arch v whorl [1], ch.5.
Hnh-31. S khi m t thut ton phn loi vn tay.
7.1. Trch chn c tnh Phn loi vn tay th ph thuc nhiu vo cc im k d (singular point), bao gm im delta v im core. Khi c orientation image cc im k d c th xc nh thun li bng phng php Poincar. c tnh cn trnh chn l gc nh hng cc b qi , j [1, 3, 8].
a)
b)
Hnh-32. Phng php ch s Poincar: a) trong min lin tc; b) trong nh s.
44
7. PHN LOI VN TAY Ch s Poincar ca trng nh hng ti im nh [i, j ] theo mt ng bao kn tnh nh sau:Poincar ( i, j ) = d d ( k ) , D ( k ) = p + d d ( k ) , p - d d ( k ) , 1 2p
D ( k ),k =0
N
p , 2 p dd ( k ) , 2 p dd ( k ) - , 2dd ( k ) > myGuifv c ca s giao din trong Hnh-40
Hnh-40. Ca s giao din.
Bc 2: Click vo nt Open, chon mt file nh vn tay bt u trch chn c tnh.
Hnh-41. M mt file nh.
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PH LC Bc 3: Click vo nt HE Enhancement thc hin tng cng nh bng cn bng lc xm.
Hnh-42. Cn bng lc xm.
Bc 4: Click vo nt FB Enhancement thc hin tng cng nh bng bin i Fourier ri rc v cn bng cng sng ca nh.
Hnh-43. Bin i Fourier ri rc v cn bng cng sng.
58
PH LC Bc 5: Click vo nt Binarization thc hin phn ngng cc b-nh phn ha nh.
Hnh-44. Nh phn ha nh.
Bc 6: Click vo nt Orientation Image c lng trng nh hng.
Hnh-45. Trng nh hng.
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PH LC Bc 7: Click vo nt Segmentation khoanh ly vng nh vn tay.
Hnh-46. Segmentation.
Bc 8: Click vo nt Detection Core tm im core.
Hnh-47. Pht hin core.
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PH LC Bc 9: Click vo nt Thinning lm mnh ng vn.
Hnh-47. Lm mnh ng vn.
Bc 10: Click vo nt Post-processing lc cc minutiae.
Hnh-48. Lc minutiae.
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PH LC Bc 11: Click vo nt Display Minutiae hin th cc minutiae s to m.
Hnh-49. Hin th minutiae.
Bc 12: Click vo nt Matching i snh vn tay.
Hnh-50. i snh vn tay.
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