GIỚI THIỆU VÊ TRUYỀN HÌNH.doc

7/31/2019 GII THIU V TRUYN HNH.doc

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MC LCPHN I:GII THIU TNG QUAN V TRUYN .................................1

Chng I: Gii thiu truyn hnh en trng ...........................................................1I. H thng truyn hnh ....................................1II. Nguyn l lm vic ca h thng truyn hnh en trng..............................1Chng II: Nguyn l truyn hnh mu...................................2I. Gii thiu ......................................2II. S khi h thng truyn hnh mu.................................3III. Nguyn l h thng truyn hnh mu.................................3IV. S khi pha pht tn hiu mu v nguyn l lm vic.............................4IV.1 Nguyn l lm vic...................................4IV.2 S khi pha pht...................................4

V. S khi v nguyn l lm vic ca pha thu..............................6V.1 Nguyn l ca khi thu hnh..................................6V.2 S khi ca my thu...................................6Chng III: c im ca tn hiu hnh..................................9I. Hnh dng ca tn hiu hnh..................................9II. Ph tn hiu hnh..................................10II.1 Xc nh tn ph ca tn hiu hnh l xc nh cc thnh phn xoay chiu catn hiu..............................................................................10II.2 Hnh dng ph ca tn hiu hnh...................................10Chng IV: Cc dng mo trong truyn hnh....................................10

I. S hnh thnh tn hiu hnh v mo aperture..................................10II. nh hng ca nhiu n cht lng nh truyn hnh...............................11III. Cc loi mo v can nhiu trong h thng truyn hnh mu ............................11PHNII: TM HIU K THUTCHUYN I TN HIU T TNGTSANG TN HIU S TRONG TRUYN HNH....................12Chng I:Gii thiu truyn hnh s......................................12I. Ti sao phi chuyn i t tn hiu tng t sang tn hiu s...................12II. Nguyn l cu to ca h thng v cc thit b truyn hnh s.....................12II.1 Nguyn l ca h thng truyn hnh s..................................13

II.2 Mt s c im ca thit b truyn hnh s................................13Chng II: Bii i tn hiu tng t s (A/D) v tn hiu s tng t. ............14I. Ly mu tn hiu tng t...................................14II. Cu trc ly mu.....................................18II.1 Cu trc trc giao.....................................18II.2 Cu trc Quincunx mn....................................19II.3 Cu trc Quincunx dng....................................20II.4 Ly mu tn hiu Video...................................20II.4.1 Chun 4:4:4......................................21II.4.2 Chun 4:4:2......................................21


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II.4.3 Chun 4:2:0......................................22II.4.4 Chun 4:1:1......................................23

III. Lng t ho tn hiu Video....................................23III.1 Khi nim.....................................23III.2 Qu trnh bin i AD l lng t ho.................................23IV M ho........................................2IV.1 nh ngha m ho.....................................27IV.2 Cc c tnh c bn ca m...................................2IV.3 Cc m s cp.....................................29Chng III: Nn nh s.......................................30I. Mc ch nn......................................30II. Thc cht ca nn Video s....................................30

II.1 M hnh nn nh......................................31II.2 d tha d liu......................................3II.2.1 D tha m (coding redun dancy)..................................33II.2.2 D tha trong pixel(inter pixel redun dancy).................................33II.2.3 D tha tm sinh l.....................................33III. Cc phng php nn.....................................34III.1 Nn khng tn hao.....................................34III.1.1 M ho vi di t m thay i (VLC)..................................34III.1.2 M ho vi di ca t m ng (RLC).................................34III.1.3 S dng khong xo dng v mng...................................34

III.2. Nn c tn hao......................................35IV. Cc loi m dng trong nn...................................35IV.1 M RLC (Run length Coding)..................................35IV.2 M Shannon-fano.....................................36IV.3 M Huffman.....................................36IV.4 M d on(DPCM)....................................36IV.4.1 DPCM trong mnh (intsaframe DPCM)...............................37IV.4.2 DPCM gia cc mnh...................................37IV.4.2.1 intraframe DPCM....................................38IV.4.2.2. Phng php lm y c chn lc (Selective replenishment) ...............38

IV.4.2.3. Phng php chia thnh nhng phn nh chuyn ng v tnh .............38IV.5. Phng php m chuyn v (transform coding) ...............................39V. Nn trong nh ......................................411. Nguyn l nn trong nh.....................................412. Tin x l.......................................413. Bin i cosin ri rc (DCT)....................................434. Lng t ho......................................45. M ho entropy......................................45VI. Nn lin nh .....................................................................................................451. M hnh ..............................................................................................................46


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2. Xp x v b chuyn ng .................................................................................463. Tc truyn sau khi nn. .....................................48

VII. Cc chun MPEG .................................................................................491. gii thiu chung v chun MPEG. .....................................................................491.1 nh loi I(nta-picture) ......................................................................................491.2. nh loi P( predicter- picture) ..........................................................................491.3 nh loi B(Bidiretional predcited-picture) ........................................................491.4 Nhm nh (GOP)..............................................................................................491.5. Cu trc dng bit MPEG video........................................................................511.6 Nguyn l nn dng bit ....................................................................................522. Tiu chun MPEG-1 ..........................................................................................542.1 Tiu chun MPEG-2 ........................................................................................54

CHNG III: AUDIO S V CC TIU CHUN NN AUDIO S54I. Khi nim m thanh ............................................................................................54II. Pht tn hiu m thanh .......................................................................................55II.1.1.S khi my pht tn hiu m thanh .........................................................55II.1.2 Chc nng tng khi .....................................................................................55II.2. Su ch tiu cht lng cho my pht tn hiu m thanh .................................56II.2.1. n nh tn s ........................................................................................56II.2.2 Mo tn s ...................................................................................................56II.2.3 Mo phi tuyn ...............................................................................................57II.2.4 su iu ch.............................................................................................57

II.2.5 Mc bc x sng hi .....................................................................................57II.2.6 Mc tp m v ting ...................................................................................57II.3. Nguyn l ghi m ..........................................................................................58II.3.1 Cc phng php ghi m ..............................................................................58II.3.2 Cc ch tiu cht lng ca my ghi m ......................................................581. Tc chuyn bng nh dng ...........................................................................582. Mc sai iu ......................................................................................................583. Di tn s cng tc .............................................................................................584. Mo tn s .........................................................................................................595.Mo khng ng thng ......................................................................................59

6. Cng xut danh nh...........................................................................................597. nhy u vo .................................................................................................598. Di ng .............................................................................................................59II.3.3. Nhc im ca phng php ghi tn hium thanh tng t .......................................................................................60III. Khi nim c bn ca audio s .........................................................................601. M ho knh truyn ............................................................................................602. c im ca tn hiu s liu AES/EBU ............................................................613. Cc c im dao din knh truyn AES/EBU. ..................................................62


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4. Gii m v cc knh tn hiu AES/EBU .............................................................625. ng b audio s ...............................................................................................63

6. ng b gia cc tn hiu audio s ....................................................................637. ng b gia tn hiu audio s v tn hiu video ...............................................647.1 Ghi audio s ....................................................................................................647.2 Khi nim k thut nn s liu audio ...............................................................657.3 K thut nn s liu audio ................................................................................667.3.1. Nn khng tn hao ......................................................................................667.3.2. Nn tn hiu s c tn hao ............................................................................678. Nn tn hiu audio theo chun MPEG ................................................................678.1 Tiu chun nn MPEG-1 (ISO/LEC 11173) .....................................................678.2 Thut ton nn tn hiu audio MPEG bao

gm cc bc sau ............................................................................................698.3.1. c im ca mc I ......................................................................................708.3.2. c im ca mc II ....................................................................................718.3.3. c im ca mc III ...................................................................................718.3.4. Chun nn MPEG2. ......................................................................................728.4. u im ca hai tiu chun MPEG .................................................................72Kt lun .................................................................................................................74Thut ng ting anh ................................................................................................75


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PHN I: GII THIU TNG QUAN V TRUYN HNH

CHNG I : GII THIU TRUYN HNH EN TRNG

I.H thng truyn hnh:

L mt tp hp cc thit b m bo cc qu trnh pht v thu cc hnh nh trng

thy. Truyn hnh c dng vo nhiu mc ch khc nhau. Tu theo mc ch catruyn hnh v xc nh ch tiu k thut ca h thng cho ph hp.Yu cu chung l nh nhn trn mn my thu hnh phi phn nh trung thc vt cntruyn i. Nhng cht lng nh cng cao th thit b ca h thng truyn hnh cng

phc tp, cng knh t tin. V vy khi thit k cc h thng truyn hnh phi dungha cc ch tiu v cht lng nh v kch thc v kinh t. Song d vi bt k hthng truyn hnh no cng c s khi tng quan nh sau.

H1: S khi tng qut h thng truyn hnh en trng

II. Nguyn l lm vic ca h thng truyn hnh en trng

nh ca vt cn truyn i qua h thng quang hc ca my quang (camera) hi t

trn catt ca quang in ca b chuyn i nh tn hiu. b chuyn i ny nhquang c chuyn i thnh tn hiu in tc l chuyn i nng lng nh sngthnh nng lng in.

Hnh nh l tin tc cn truyn i, tn hiu in mang tin tc v hnh nh c gi ltn hiu hnh hay cn gi l tn hiu video. Qa trnh chuyn i nh quang thnh tnhiu in l qu trnh phn tch nh. Dng c ch yu thc hin s chuyn i nyl phn t bin i quang in , hay cn gi l ng pht hnh.

Tn hiu hnh c khuch i, gia cng ri truyn i theo knh thng tin (hu tuyn

hoc v tuyn) sang ph thu. pha thu tn hiu hnh c khuch i ln n mc

cn thit ri a n b chuyn i nh. B chuyn i nyc tc dng ngc li pha pht, n chuyn i tn hiu hnh nhn c thnh nh quang (chuyn i nnglng in thnh nng lng nh sng). Qu trnh chuyn i tn hiu thnh nh

ngknhcnhvt A

Hnh nhA

B

chuyni nhtn hiu

Bkhuch

i v giacng tn

hiu

Knhthng

tin

Bkhuchi tnhiu

Bchuyni tn

hiu nh

B toxung

ng b

B tchxung

ng b


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quang l qu trnh tng hp nh hay khi phc nh. Dng c thc s chuyn iny l phn t bin i in quang cn gi l ng thu hnh .

Qu trnh truyn i tn hiu nh phi han tan ng b v ng pha vi qu trnhchuyn i nh tn hiu th mi khi phc c nh quang truyn i. thc hinc s ng b v ng pha, trong h thng truyn hnh phi dng mt b to xung

ng b. Xung ng b c a n b chuyn i nh tn hiu khng ch, qutrnh phn tch nh. ng thi a n b khuych i v gia cng tn hiu hnh cng vi tn hiu hnh ri truyn sang pha thu, xung ng b tch ra khi tn hiutruyn hnh v dng khng ch qu trnh tng hp nh(khi phc nh).

CHNG II : NGUYN L TRUYN HNH MU

I. Gii thiu.

i vi h thng truyn hnh en trng thc hin phn tch hnh nh cntruyn thnh cc mu ri rc ri truyn ln lt cc mu . Thng tin c truyn il thng tin v chi ca im nh. Ti pha thu s khi phc li hnh nh truyn ithnh mt nh en trng. Tuy nhin cnh vt quanh ta cha nhiu mu sc v vytruyn hnh cn phi truyn i c cc thng tin v mu sc ca nh sao cho phathu c th khi phc c thnh hnh nh c mu sc nh thc t .

Vn t ra cho k thut truyn hnh mu l lm th no khng tng s knh thngtin m vn truyn c hnh nh mu hay ni cch khc bin hnh nh mu thnhmt tn hiu in bin i theo thi gian, c th truyn i bng mt knh thng tin.

I. S khi h thng truyn hnh mu.

H 2 . S tng quan v h thng truyn hnh mu.

Hiuchnh

gam mu

Mchma trn B iu

ch mu

Mchcng

s2 Uc

Ur

Gb

G

UM= Uy+ Uc

B chon tnhiu B tch

sng

Mch matrn

ngthu

uy

B tchsng hnh


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III. Nguyn l h thng truyn hnh mu:

Hnh nh cn truyn qua camera truyn hnh mu c bin i thnh 3 tnhiu mu c bn UR , UG, UB, nh hnh trn. Cc tn hiu mu c bn ny ca qua cc mch hiu chnh gamma, cc mch ny s dng b mo gamma dong thu pha bn thu gy nn. Cc tn hiu b mo UR, UG, UB c a vo

mch ma trn to ra tn hiu chi UY v 2 tn hiu mang mu S1, S2 . Cc tn hiuS1, S2 iu ch dao ng tn s mang ph to ra tn hiu mang mu cao tn UC.Trong b cng cc tn hiuUY v U c trn vi nhau tr thnh tn hiu truynhnh mu tng hp. UM = UY +UC Tn hiu UM ny c truyn n bn thu bngcp, h thng viba hoc my thu pht v tuyn in.

Qu trnh bin i cc tn hiu mu c bn UR,UG,UB thnh tn hiu truyn hnhmu tng hp UM gi l qu trnh m ho tn hiu mu.Pha bn thu tn hiu UM, nhn c sau (tch sng video)bin i thnh cc tn hiu

mu c bn UR , UG , UB . Qu trnh bin i ngc gi l qu trnh giim tn hiu mu.

Qa trnh gii m thc hin trong phn tn s video ca my thu hnh mu tn hiutruyn hnh mu tng hp UM nhn c sau tch sng c lc ra t tn hiu chiUY v tn hiu mang mu UC. Sau b tch sng mu, ta thu c tn hiu mang muS1v S2 l cc tn hiu s mu.

Nh c mch ma trn tn hiu UY, S1 ,S2 to ra tn hiu mang mu c bn UR,UG,UB (hoc tn hiu UR - UY, UG - UY, UB- UY ) phn t cui cng l ngthu, y bin i cc tn hiu mu thnh hnh nh phc tp.

IV . S khi pha pht truyn hnh mu v nguyn l lm vic.IV.1 Nguyn l lm vic.

nh mu cn truyn i trc ht c h thng knh quang hc v knh lcmu phn tch thnh 3 chm tia mu c bn: mu R(red), mu lc G ( Green)vmu lam B (Blue). Ba chm tia ny phn bit tc ng ln 3 n quang in ithnh tn hiu in ca 3 mu c bn, ER, EG, EB, (nu cc tn hiu in ny c sa mo g, do qu trnh chuyn i quang in gy ra th s c thm du

phy trn (ER, EG, EB) 3 n quang in c th l n vidicon, n supeorticon

hoc C.C.D kt hp gia truyn hnh mu v truyn hnh en trng cc tn hiu ER ,EG EB, khng c gi trc tip n my thu m c a ti mt mch ma trn ithnh tn hiu chi EY v hai tn hiu mu l ER-EY v EB- EY. Tn hiu EY chnhl tn hiu hnh nh trong truyn hnh en trng. Hai tn hiu mu cn li s a qua 1mch to m mu ca cc h mu khc nhau l h NTSC , h PAL v h SECAN t hp li thnh tn hiu mu C. Tn hiu mu C sau c lng vo trong ph tnca tn hiu chi ri tt c c iu ch bin vo my pht sng mang hnh nhfA. Tn hiu m thanh cn truyn i c iu tn vo sng mang c tn s fT. Sau

cng phi hp vi sng fA a anten pht sng. Tn s fT lun cao hn tn sfA(6.5MHZ i vi h OIRT) cn cng sut my pht hnh ln gp 10 ln cng sutmy pht m thanh.


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IV.2 S khi pha pht .

V. S KHI V NGUYN L LM VIC CA PHA THUV.1 Nguyn l ca khi thu hnh.Gm 6 phn: Phn cao tn- trung tn- tch sng gm cc khi t 1 n 6.


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Khi 1: Hp knh ca bng UHF.Khi 2: Hp knh ca bng VHF.

Khi 3: Mch khuch i trung tn chung.

Khi 4: Tch sng video v khch i s b sau tch sng video.

Khi 5: Mch t ng iu chnh tn s ngoi sai.Khi 6: T ng iu chnh h s khuch i AGC. Phn ng ting.

Khi 7: Quy i v to trung tn ting ln 2 c th thu c ting ca cc h mukhc nhau.Khi 8: Ton b ng ting ca tivi. Phn ng hnh.Khi 9: Khuch i v x l tn hiu chi EY. Khi 10: Mch gii m mu.Khi 11: Mch ma trn G -Y.

Khi 12: Mch ma trn R,G,B khi phc li 3 tn hiu mu c bn l ER, EG,EB.Khi 13: Mch khuch i tn hiu mu ln cui.

Khi 14: Mch khch i tn hiu mu lc ln cui.

Khi 15: Mch khuch i tn hiu mu lam ln cui.

Khi 16: Mch cn bng mu trng . Phn ng b v to xung qut .

Khi 17: Mch tch xung ng b, khuch i v phn chia xung ng b.

Khi 18:Tan b khi qut dng ca ti vi

Khi 19:Tan b khi qut mnh ca ti vi.Khi 20: Mch phi hp gia xung qut dng vi xung qut mnh

Khi 21:Mch phi hp hnh thnh xung i xo tia qut ngc.Khi 22: Mch chnh lu i cao p. Phn vi s l iu khin.

Khi 23: Mch tip nhn lnh iu khin t xa bng tia hng ngoi.

Khi 24: Mch vi s l iu khin cc hot ng ca ti vi.

Phn ngun:

Khi 25: Mch kh t.Khi 26: Bao gm cc mch chnh lu lc v n p to ra cc mc

in p mt chiu n nh cn thit nui ti vi.

V.2 S khi ca my thu.


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CHNG III: C IM CA TN HIU HNH

I.Hnh dng tn hiu hnh .

Tn hiu hnh l tn hiu n cc tnh bi v chi ca nh c tr s dngbin i t khng n tr s dng cc i. Do tn hiu hnh tng ng cngch c mt cc tnh hoc l dng hoc l m.

Nu ng vi im trng ca nh, tn hiu c tr s in p ln nht, ng vi imen, tn hiu c in p nh nht th gi l tn hiu cc tnh dng. Nu ngc li gil cc tnh m, ni cch khc tn hiu hnh c cha thnhphn mt chiu (tr trung

bnh ). Tr trung bnh ca tn hiu i vi mi dng t l vi chi trung bnh cadng , tr trung bnh ca tn hiu i vi mi nh t l vi chi trung bnh canh . i vi nh ng im, chi trung bnh khng thay i ,do tr trung bnhca tn hiu cng khng thay i .Tn hiu hnh ni chung l tn hiu khng chu k. Ch trong trng hp truyn

nh khng di ng th tn hiu c chu k, bng chu k tn s nh, trng hp c bitkhi truyn nhng di sc thng ng bt ng th chu k lp li ca nh bng

chu k dng.

H5.Tn hiu y


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II.Ph tn hiu hnh.II.1 Xc nh tn ph ca tn hiu hnh l xc nh cc thnh phn xoay chiuca tn hiu.

xc nh di tn ph ca tn hiu hnh trc ht ta xc nh gii hn div trn ca tn ph tc l thnh phn thp nht v thnh phn cao nht ca tn ph

II.2Hnh dng ph ca tn hiu hnh .

Ph tn hiu hnh ch cn thnh phn tn s mt v cc hi bc cao ca n. Nichung tn hiu hnh l tn hiu khng chu k (i vi nh ng). Nhng nu truynnh bt ng tn hiu hnh c tnh chu k, tnh chu k l do nguyn l qut quytnh. Lc qut lin tc, tn s lp li ca tn hiu hnh bng tn s nh. Lc qut xenk c th tch gn ng bng tn s lp li ca tn hiu hnh bng tn s mnh.CHNG IV: CC DNG MO TRONG TRUYN HNH

Trong h thng truyn hnh nh quang c chuyn thnh tn hiu hnh,hay cc thng tin v nh c m ho thnh cc mc khc nhau ca tn hiu hnh.Bt k mt dng mo no i vi tn hiu hnh cng u gy ra mo nh li ra hthng. V vy m bo tnh trung thc ca h thng truyn hnh cc thit b truyntn hiu phi khng gy ra mo hoc mo khng ng k.I.S hnh thnh tn hiu hnh v mo aperture .

Mt trong nhng yu cu i vi ng truyn (thit b ng knh, knhthng tin ) l di thng phi rng cho tan b tn ph ca tn hiu hnh i qua.

Nu di thng khng rng, mt phn tn ph ca tn hiu hnh b ct, hoc di

thng rng i vi tan b tn ph ca tn hiu hnh nhng cc thnh phn phkhng c khuch i nh nhau, th tn hiu hnh s b mo, nh li ra ca hthng cng b mo, mo gi l mo tn s.

Mo tn s do thit b gy ra c nh gi bng c tuyn tn s hoc ctuyn qu ca thit b , y dng c tuyn qu kho st .

c tuyn qu c chia lm hai khong kho st, khong thi gian ngn v

khong thi gian di Thi gian c di xp x bng thi gian truyn mt phn tnh l thi gian ngn. Thi gian xp x hoc di hn thi gian truyn na dng (na

chu k dng) l thi gian di.II. nh hng ca nhiu n cht lng nh truyn hnh.

Nhiu nh hng n cht lng nh truyn hnh v nhiu mt gy ra hintng bng ma trn hnh nh, gim r ca nh, lm mo nh ... c th chia nhiuthnh bn loi:- Nhiu c tnh chu k.

- Nhiu xung .

- Nhiu chi bin i chm .

- Nhiu ht .

III. Cc loi mo v can nhiu trong h thng truyn hnh mu.

Tn hiu chi trong thuyn hnh mu chu nhng loi mo nh truyn hnh en

trng nh mo gamma, mo tn s, mo pha ...


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Cc loi mo v can nhiu ph thuc vo phng php truyn ng thi cc loi tn

hiu v i vi cc h truyn hnh khc nhau, chng c cc quan h khc nhau.

S mo tn hiu chi c truyn i bng mt knh ring bit, vy tn hiu chikhng chu nh hng ca tn hiu mang mu. Nhng do h thng truyn tn hiukhng han thin nn tn hiu chi b mo.

Mo tn hiu mang mu to nn s sai mu, mc nhiu ph thuc tnh chttn hiu chi di tn knh tn hiu mu.

PHN II: TM HIU K THUT CHUYN I TN HIU T TNG TSANG TN HIU S TRONG TRUYN HNH CHNG

I:GII THIU TRUYN HNH S.

I. Ti sao phi chuyn i t tn hiu tng t sang tn hi s.

V s dng phng php s to lu tr v truyn tn hiu ca chng trnh

truyn hnh trn knh thng tin m ra mt kh nng c bit rng ri cho cc thit btruyn hnh lm vic theo cc h truyn hnh c nghin cu trc m, tn hius c kh nng thc hin c cc chc nng m tn hiu tng t hu nh khngth lm c hoc rt kh thc hin nht l trong vic x l tn hiu v lu tr chiu qu cao hn so vi tn hiu tng t nh b lc. Mc d th trong k

thut pht trin cng nghip truyn hnh trn th gii nhm t c mt s thngnht chung, l mt h thng truyn hnh han tan k thut s c cht lng cao vd dng phn phi trn knh thng tin. H thng truyn hnh k thut s v ang

c pht trin trn tan th gii to nn mt cuc cch mng tht s trong cngnghip truyn hnh.

II. Nguyn l cu to ca h thng v cc thit b truyn hnh s.

h.6:S cu trc tng qut ca h thng truyn hnh s


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II.1 Nguyn l ca h thng truyn hnh s.u vo ca thit b truyn hnh s s c tip nhn tn hiu truyn hnh

tng t. B bin i tn hiu tng t thnh tn hiu s (A/D) s bin i tn hiutruyn hnh tng t thnh tn hiu truyn hnh s cc tham s v c trng ca tnhiu ny c xc nh t h thng truyn hnh la chn.

Tn hiu truyn hnh s ti u ra b bin i A/D c a ti b m ho ngun, tiy tn hiu truyn hnh s c tc dng bt cao s c nn thnh dng bt c tc thp hn ph hp cho tng ng dng. Dng bt ti u ra b m ho ngun ca ti thit b pht (m ho knh thng tin v iu ch tn hiu ) truyn ti bn thuqua knh thng tin .Khi truyn qua knh thng tin, tn hiu truyn hnh s c m ho knh. M hoknh m bo chng cc sai st, trong tn hiu trong knh thng tin khi tn hiutruyn hnh s c truyn i theo knh thng tin, cc thit b bin i trn c gil b iu ch v b gii iu ch.

M ho trong knh thng tin c ph bin khng nhng trong ng thng tinm trong c mt s khu ca h thng truyn hnh s, v d nh my ghi hnh s, giacng tn hiu truyn hnh s.Ti bn thu, tn hiu truyn hnh s c bin i ngc li vi qu trnh s lti pha pht. Gii m tn hiu truyn hnh thc hin bin i tn hiu truyn hnh sthnh tn hiu truyn hnh tng t. H thng truyn hnh s s trc tip xc nh cutrc m ho v gii m tn hiu truyn hnh .II.2 Mt s c im ca thit b truyn hnh s .

Thit b truyn hnh s dng trong chng trnh truyn hnh l thit b nhiuknh, ngai thit b truyn hnh cn c cc thng tin km theo gm cc knh mthanh v cc thng tin ph, nh cc tn hiu in bo, thi gian chun tn s kim tra,hnh nh tnh. Tt c cc tn hiu ny c ghp vo cc khong trng ca ngtruyn nh b ghp knh .

Truyn tn hiu truyn hnh s c thc hin khi c s tng quan gia cc knhtn hiu, thng tin ng b s c truyn i ng b cc tn hiu . kim tra tnh trng thit b truyn hnh s s dng cc h thng o kim tra tng

t nh i vi h thng truyn hnh tng t.a/ Yu cu v bng tn:Bng tn ca truyn hnh s rng hn rt nhiu so vi bng tn ca truyn hnh tngt.

b/T l tp m :u im ln nht l kh nng chng nhiu tt .c/ Mo phi tuyn:Khng b nh hng ca mo phi tuyn trong qu trnh ghi cng nh trong qu trnhtruyn .d/ Gi thnh v thit b phc tp, t.e/ X l tt c cc tn hiu m tn hiu tng t khng th lm c hoc kh lm


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c.

CHNGII: BIN I TN HIU TNG T S (A/D) V TN HIU S

-TNG T.

Thc hin vic chuyn i tn hiu tng t s (A/D) qua cc bc sau:

I.Ly mu tn hiu tng tL qu trnh gin on (ri rc ho ) theo thi gian bng tn s ly mu flm,

kt qu l mt chui cc mu. Ly mu l bc u tin th hin tn hiu tng tsang s. V cc tn s ly mu chn s ch ra to ca cc im . Qa trnh

bin i ny phi tng ng v mt tin tc ca dng tn hiu vo.

Bin tn hiu tng t c ly mu vi chu k flm thu c mt chui cc xunghp vi tn s ly mu c tnh bng.

H7. Ph ca tn hiu ly mu

Qu trnh ly mu tng ng vi mt qu trnh iu bin tn hiu (fo)trnsng mang c tn s bng tn s ly mu (flm) qu trnh iu bin to ra cc bin trnv bin di. Song ly mu c dng hnh ch nht ph ca n bao gm thnh phntn s ly mu v cc hi ca n hnh trn.Thc t vic ly mu tn hiu da trn c s ca nh l Nyquist-shamen. Tn hiux(t) lin tc theo thi gian c ph hn ch ct ti w han tan c xc nh bngmt dy cc gi tr tc thi ly cch nhau mt on.T=Tmin(1/2fc) vi fc= wc/2P

Hm x(t) xc nh trong khong (to, to+t) s han tan c xc nh t cc muri rc x(kt) ca n theo biu thc.


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V mt ton hc c th m rng v pha tn s m cho cc tr s m ca k. Vikhong cch ly mu t nh hn hoc bng P/wc: t P/wc, trong wc l tn scao nht trong ph ca hm x(t).

H.8.Ph ly mu l tng

Tn hiu ly mu cha trong n tan b thng tin mang tn hiu gc nu tnhiu gc c bng tn hu hn, tc l n khng c nhng phn t s c tn s nmngai mt tn s fc no .


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Tn s ly mu phi bng hoc ln hn hai ln fc tc l 2fsa 2fc.

Hnh trn minh ha ph tn s ly mu l tng khi tn hiu bng c bn c di thngfc v tn s ly mu 2fc. Nh vy di bin trn v bin di u c di thng l fcvi tn s ny khng xut hin nhiu bng c bn v di bin di.Hnh 4: Minh ho trng hp ly muvi tn s nh hn 2fc. Mt phn di bin

di ca tn hiu ly mu chng ln ph ca tn hiu bng c bn (do nguyn nhngy nn hin tng mo chng ph )

H9: Mo do chng ph

Tn hiu video, do cc c trng ring nn ngai vic tho mn nh l ly mu

Nyquyst, qu trnh ly mu cn phi tho mn cc yu cu v cu trc ly mu, tnhtng thch gia cc h thng. Qu trnh ny phi xc nh c tn s ly mu, cutrc ly mu cn phi t c ch tiu v cht lng nh, tnh tng thch gia cch truyn hnh, tc bit thch hp v mch thc hin n gin.

i vi tiu chun tn s Nyquyst, vic ly mu tn hiu video vi tn s flm


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ffsa fgh0 fgh fsa

h10.Bng tn bo vVic chn tn s ly mu ti u s khc nhau vi c thnh phn tn hiu khc: tnhiu chi, tn hiu mu c bn, tn hiu mu v tn hiu vi deo tng hp. Tn s lymu cng ph thuc vo cc h thng truyn hnh mu.Tn hiu video tng hp c ly mu vi tn s bng bi s ca tn s sng mang

ph. Khi tn s ly mu bng 3f sc,vi h NTSC c tn s ly mu l 10,7MHz v hPAL l 13,3MHz. Khi tn s ly mu l 4fsc, vi h NTSC tng ng c tn s lymu l 14,3MHz v h PAL 17,7MHz. Tn s ly mu cng cao cng d dng chovic s dng cc b lc trnh chng ph v b lc ti to cng nh a li mt c

tuyn tn s tt hn. K thut hin nay cho php gim nh cc kh khn trong victhit k cc b bin i A/D bng vic s dng thit b ly mu tn s cao .

i vi h SECAM do x dng phng php iu tn, nn qu trnh s ho tn hiuvideo khng thc hin ly mu tn hiu tng hp. Tn hiu SECAM c m hothnh tn hiu thnh phn tng t c ly mu ti tn s bng bi s ca tns dng qut.

II: Cu trc ly mu.

Tn hiu hnh nh t camera v c hin th trn mn hnh cha thng tin v ng

b theo mnh v dng l cc nh hai chiu.Vy khi phc chnh xc hnh nh,tn s ly mu c lin quan n tn s dng v tn s ly mu phi l bi ca tn sdng. Vi quan h ny im ly mu trn cc dng qut k nhau s thng hng vinhau v trnh c cc hiu ng ng bin gy ra.

Nh vy vic ly mu khng ph thuc vo vic ly mu khng ph thuc theo thigian m cn ph thuc vo to cc im ly mu.V tr cc im ly mu hay cutrc ly mu c xc nh theo thi gian, trn cc dng v cc mnh. Hm ly muc th bin i dng xq(t,x,y), tn s ly mu ph hp vi cu trc ly mu s cho

php khi phc hnh nh tt nht.V vy tn s ly mu phi thch hp cho c ba chiu t, x, y. Tuy nhin trong

cu trc ly mu ph bin, ta ch xt cc mu c biu din bng hai i lng(x, y).

C ba dng lin kt v tr cc im ly mu c x dng ph bin cho cu trc lymu tn hiu video.II.1 Cu trc trc giao.

c sp xp trn cc dng, mnh k nhau thng hng theo chiu ng . Cu trc

ny l c nh theo mnh v theo hai nh (hai mnh)


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H11: Cu trc trc giao

Trong trng hp ny tn s ly mu thoa mn nh l Nyquist v do cn sdng tc bt rt ln.

II.2 Cu trc Quincunx mnh.

Cu trc quincunx

i vi cu trc quincux, cc mu trn cc dng k nhau thuc mt mnh xp thnghnh theo chiu ng (trc giao), nhng cc mu thuc mnh mt li dch i mt nachu k ly mu so vi cc mu ca mnh th hai .Phn b ph tn ca cu trc quincux mnh rt c ngha i vi mnh mt n cho

php lm gim tn s ly mu theo dng. Ph tn cu trc ni trn mnh hai so vimnh mt b dch v c th lng vi ph tn c bn gy ra mo cc chi tit nh (khihnh nh c cc sc hoc cc ng thng ng).

II.3 Cu trc quincux dng.Cc mu trn cc dng k nhau ca mt mnh s lch nhau na chu k ly mu, cn ccmu trn dng mt mnh lch so vi cc mu trn dng tip sau (ca mnh sau) mt


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na chu k ly mu. y khng xy ra trng hp lng cc ph chnh v khng bmo iu cho php s dng tn s ly mu nh hn 25% tn s Nyquist v tit kimc rng ph ca tn hiu s .

Tu theo cu trc ly mu, s xut hin loi mo nh c trng. Vi cu trc trc giao, phn gii nh s gim. i vi cu trc Quincunx s xut hin cc im

nh .Ngc li vi cu trc Quincunx dng s xut hin cc vng trn theo chiungang

H12: Cu trc quincunx dng.

Tm li cu trc trc giao cho cht lng nh cao nht v i vi mt ngi th phn gii gim d chu hn l hai loi mo nu trn.

II.4 Cc chun ly mu tn hiu video.Qa trnh ly mu l bc u tin ca vic s ho tn hiu video, trc ht ta

tm hiu v mt vi tiu chun ly mu. C nhiu tiu chun video s thnh phn,im khc nhau c bn gia chng t l gia tn s ly mu v phng php lymu tn hiu chi v tn hiu mu, trong bao gm: Tiu chun 4 : 4 : 4,4 : 2 :2,4 : 2

: 0, 4 : 1 : 1. Di y ta xt phng thc tng chun tc ly mu da trn cs tn s chun l 3,375 MHz.II.4.1 Chun 4:4:4.

Mu tn hiu ch c ly i vi cc phn t tch cc ca tn hiu video. Vih PAL, m hnh c chia lm 625x720 im (pixel).


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Cc tn hiu chi (Y), tn hiu mu (CR,CB) c ly mu ti tt c cc im lymu trn dng tch cc ca tn hiu video. Cu trc trc giao, v tr ly mu nhtrnh by hnh v trn.

Tiu chun 4 : 4 : 4 c kh nng khi phc hnh nh cht lng tt nht trong cc tiu

chun, thun tin cho vic x l tn hiu. Tiu chun ny c th dng trong trnghp x l tn hiu chi v tn hiu mu RGB. N c th c dng trong studio nhmri rc ho tn hiu. Tuy nhin tiu chun ny s i hi tc bt cao. Cc t chctiu chun quc t thng nht v ch tiu tn s ly mu cho truyn hnh s theotiu chun ny vi tn gi l CCIR-601.Vi tiu chun 4 : 4 : 4 tc bt d liu (v d cho h PAL) c tnh nh sau.

* Khi ly mu 8 bit: (720 + 720 + 720) x 576 x 8 x 25 = 249 Mbit/s.

*Khi ly mu 10 bit:(720 + 720 + 720) x 576 x 10 x 25 = 311 Mbit/s

II.4.2 Tiu chun 4 : 2 : 2.

im u ly mu tan b ba tn hiu: Chi (Y) v tn hiu mu (CR,CB)im k tip ch ly mu tn hiu chi Y, cn hai tn hiu mu khng ly mu. Khigii m mu suy ra t mu ca im nh trc.im sau na l ly mu ba tn hiu Y, CR, CB.Tun t nh th, c bn ln ly mu tn hiu chi Y, th hai ln ly mu CR, hai lnly mu CB to nn c cu 4 : 2 : 2.

i vi h PAL tc dng d liu theo chun ny c tnh nh sau.*Khi ly mu 8 bit: (720 + 360 + 360) x 576 x 8 x 25 = 166 Mbit/s.

*Khi ly mu 10 bit:(720 + 360 + 360) x 576 x 10 x 25 = 270 Mbit/s.

Tiu chun 4 : 2 : 2 l tiu chun c bn ca truyn hnh s. Cht lng hnh nh catiu chun ny cao hn tiu chun 4 : 4 : 4. N cho php x l tn hiu mt cchthun li.Theo chun ny, tn hiu Y c ly mu ti cc im nh ca dng, cn tn hiumu th c cch mt im s ly mu cho mt tn hiu hiu mu. Tn hiu ny c

ly xen k, nu hng chn ly mu cho tn hiu mu CR th dng s ly mu cho tn

hiu mu CB.i vi h PALtc dng d liu theo chun ny c tnh nh sau:

* Khi ly mu 8 bit (720 + 360) x 576 x 8 x 2 = 124,4 Mbit/s.


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*Khi ly mu 10 bit (720 + 360) x 576 x 10 x 25 = 155,5Mbit/s.II.4.4 Tiu chun 4 : 1 : 1.

im nh u ly mu Y, CR, CB: Ba im nh tip sau ch ly Y khngly mu CR, CB. Khi gii m mu ca ba im nh sau phi suy ra t im nh u.Tun t nh th, c bn ln ly muY, c mt ln ly mu CR, mt ln ly mu

CB y l c cu 4 : 1 : 1.

H16: Tiu chun 4 : 1 : 1.

i vi h PAL, tc dng d liu theo chun ny c tnh nh sau.

* Khi ly mu 8 bit: (720 + 180 + 180) x 576 x 8 x 25 = 124,4 Mbit/s.

* Khi ly mu 10 bit: (720 + 360 + 360) x 576 x 10 x 25 = 155,5 Mbit/s

Tiu chun ny cho cht lng hnh nh tng i thp, thng c dng cho in

thoi truyn hnh.

III. LNG T HO TN HIU VIDEO.

III.1 Khi nim

Lng t ho l qu trnh ri rc ho theo bin tn hiu ( c ri rc

ho theo thi gian ) c ngha l chia bin ra nhiu khong (mc) khc nhau v mi

mc c gn bng mt tr bin .

III.2 Qa trnh bin i AD l lng t ho .


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Trong qu trnh ny bin tn hiu c chia lm cc mc gi l mc lng

t khong cch gia hai mc k nhau gi l bc lng t. Cc mu cc t qutrnh ly mu s c bin bng cc mc lng t.Thi gian Gi tr lng t Q c xc nh theo biu thc: Q = 2N trong N l s

bit biu din mi mu.Tn hiu s nhn c l mt gi tr xp x ca tn hiu banu, nguyn nhn do qu trnh lng t ho xc nh cc gi tr s ri rc cho mimu. Hnh trn cho thy tt c cc gi tr bin nm trong gii hn ca mt mclng t u c thit lp mt gi tr nh nhau chnh l mc lng t Q. C 2

phng php lng t ho l:

Lng t ho tuyn tnh c cc bc lng t bng nhau. Lng t ho phi tuyn ccc bc lng t khc nhau. Trong hu ht cc thit b s cht lng studio, tt ccc mc lng t u c bin bng nhau, v qu trnh lng t ho c gi llng t ho ng u. y l qu trnh bin i t mt chui cc mu vi v hn

bin sang cc gi tr nht nh vy qu trnh ny gy ra sai s, gi l sai s lngt. M sai s lng t l ngun nhiu khng th trnh khi trong h thng s. Bin tn hiu vi deo bin i theo thi gian.Cc gi tr lng t c th cha sai s trong

phm vi 1/2Q trong Q l bc lng t.Trong cc h thng s dng 8 bit (v ln

hn 8 bit) d biu din mu, sai s lng t c th coi nh mt ngun tn hiu khngmong mun (nhiu) cng thm vo tn hiu trong qu trnh lng t.

Trong cc h thng s dng t hn 8 bit biu din mu, sai s lng t s nhhng nghim trng n tn hiu ban u, lm mo dng sng

(t) = |x(t) x(t)|

trong (t) l sai s lng t

x(t) l gi tr cc mu tn hiu trc khi lng t

x(t) l gi tr cc mu tn hiu sau khi lng tsai s e(t) tu thuc vo tnh thng k ca ngun tn hiu vo cc rng ca bclng t. C th xem e(t) l mt loi nhiu do qu trnh lng t ho gy ra, gi l


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mo lng t .Mo lng t ph thuc vo s mc lng t. i vi tn hiu video, mo

lng t xut hin hai dng chnh. Hiu ng ng vin v nhiu ht ngu nhin .Hiu ng ng vin xut hin nhng vng c sng thay i chm v u theo

chiu ngang, khi c nhng sc vi sng c nh chia thnh nhiu ng r

nt theo chiu ng theo ng bin. Nu tng s mc lng t, hiu ng ngvin s gim .

i vi nh c nhiu chi tit mo lng t phn b ngu nhin th hiu ng

ng vin xut hin t. Khi s dng t m 8 bit biu din mu hiu ng ng vingn nh khng cn nhn bit c na .Nhiu ht ngu nhin xut hin vng nhrng v c sng ng u l dng nhiu cc ht ging nh sng m.

Hin tng ny c th c s dng hiu chnh cht lng nh qua vic bin imo t dng ngu nhin. Tn hiudirther c nhiu dng khc nhau thng thng l dng xung ch nht , tn s bng 1/2 tn s ly mu bin bng 1/2 sng lngt. Tn hiu ny tng gp i mc ln t ho vi cc nh c din rng nhng khnggim cht lng ca nh c nhiu chi tit. Trong s ho tn hiu video, thng ngunnhiu ngu nhin trong tn hiu tng t c s dng nh tn hiu tng t dc sdng nh tn hiu dirther nh cc loi nhiu c loi b. Trong trng hp

ny, vi 8 bt m ho c th loi b c hu ht cc tp m nhiu cho tn hiuvideo .Mo xut hin trong trng hp ny l mo pha vi sai s v mo khuch i vi


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sai s. Mo vi sai s c lm gim bng cch gim bc lng t.Xc nh khong ly mu trn thang lng t ng vai tr quan trng trong vic m

bo an tan ca tn hiu. Do tn hiu vo l khng n nh cng vi cc nhiu trong

qu trnh sa. S cc bc lng t, theo ln ca sai s lng t, ph thuc

vo s bt biu din mu. Trong cc h thng s u tin, thng s dng 7 hoc 8

bt biu din mu, tng ng c 128 hay 256 mc lng t .Ngy nay, cc thit bs tiu chun studio thng s dng 10 bt cho mt mu hay 1024 mc lng t .IV. M HO

IV.1 nh ngha m ho.

L bin i n thnh tn hiu s bng vic xp xp cho mi mc tn hiu (h

m thp phn) theo h m nh phn (0v 1), v l khu cui cng c b bin iAD. Theo quan im thng k l mt qu trnh bin i cu trc ngun m khnglm thay i tin tc, mc ch l ci thin cc ch tiu k thut cho h thng truyn

tin. D liu sau m ho c u im: Tnh chng nhiu cao hn, tc hnh thnhtng ng kh nng thng qua ca knh. Qu trnh ny bin i cc mc tn hiu lng t ho thnh chui cc bt 0 v 1. di ca dy tn hiu nh phn ny,thut ng chuyn mn gi l t m nh phn c tnh bng s lng cc con s0,1, l mt trong nhng ch tiu cht lng ca k thut s ho tn hiu. N phnnh mc sng ti, mu sc ca hnh nh c ghi nhn v bin i. V nguyn tc di ca t m nh phn cng ln th qu trnh bin i cng cht lng, ngha l nc xem nh l phn gii ca qu trnh s ho. phn gii hin nay l 8

bit/mu.Cc m c s dng trong truyn hnh s c phn chia mt cch quy c thnh 4nhm l:- Cc m m ho tn hiu truyn hnh.

- Cc m truyn c hiu qu cao theo knh thng tin.

- Cc m thun tin cho mch gii m ng b cho mch bn thu.

- Cc m x l s tn hiu trong cc b phn khc nhau ca h thng truynhnh s.

Cc qu trnh m ho tn hiu truyn hnh tin tc theo knh thng tin v qu trnh giim tn hiu bn thu l c lp thm ch khng phi hp vi nhau. C ngha l cc mthch nghi cho vic biu din s ca tn hiu truyn hnh c th khng thch hptruyn theo knh thng tin cn cc m thch hp cho vic m ho tn hiu truyn hnhv truyn chng nhiu theo knh thng tin c th c gii m theo phng php rt

phc tp. V vy trong truyn hnh s thng dn n vic gii quyt vn biudin m . p ng m ho tn hiu truyn hnh v sau to li n bn thu ngi tathng dng mt loi m, cn truyn chng nhiu theo knh thng tin th dng m

khc .Khi chn cc m cho cc tn hiu ca thit b truyn hnh s cn thit th nht l slp m (cu trc ton hc ) gm cc s cho vic gii quyt bi ton t ra, th hai


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l cc phng php m ho v gii m. Trong cu trc ton hc m c chia thnhm khng chnh xc s cp v m hiu chnh, ngha l sa cha s khi truyn .Trongcc khu truyn hnh s m s cp c s dung ch yu m ho tn hiu truynhnh.

Vic truyn tn hiu truyn hnh s cn phi c thc hin vi tc chnh xc cao.

Theo nguyn nhn ny th vic chn m hiu chnh c hiu qu rt c ch n. Chng ta cng kho st ring cc gii m ngu nhin, s dng cc tnh cht vcc c im ca n trong truyn hnh s bin i cu trc ca tn hiu s, do xc thc ca vic truyn v cc nhim v khc .

IV.2 Cc c tnh c bn ca m

Qu trnh bin i rt nhiu cc im n lng t ho ca tn hiu (trong c tn hiu truyn hnh ) thnh t hp cc k hiu khc nhau gi l s m ho, cn ccnhm k hiu thng tin cch im m ho gi l m ho, cn cc nhm tn hiu thngtin cch im m ho gi l m ho.

Cc thut ng m ho v m c trng cho quy trnh ca vic i chiu tn hiutruyn hnh c lng t ho xc nh cc nhm k hiu m. ng thi trongh thng truyn hnh s, vic gia cng v truyn hnh thng tin c thc hin vi sgip ca cc tn hiu m mt hoc mt vi tham s ca n ciu ch ph hp vi m thng tin .

Cc m m cc t hp ca n bao gm mt s cc k hiu nh nhau c gi l ccm u n, cn cc m cc t hp ca n bao gm mt s cc k hiu khc nhau gil m khng u n .L thuyt m ho c hai hng nghin cu:

- Th nht l nghin cu cc cu trc m m n nng cao chnh xc ca victruyn theo knh thng tin c nhiu (nh cc m chng sai s ) .Th hai l nghin cu cu trc m trit tiu d ca tn hiu m ho trong knhthng nhiu .

- Hai hng ny ng vai tr c bit trong truyn hnh s, v vy phi hp vicc

phng php khc cho php gim v cn bn d ca tn hiu truyn hnh .

S kho st mt cch chi tit cc cu trc v cc tnh cht ca m s dng trongh thng truyn hnh s .

Khi m ha hiu chnh bng m xut x nh hn bng m knh, do vy

truyn hnh thng tin i hi phi c phn t hp tan b cc t m ca knh. Cc

t hp m c s dng ny c gi l c cho php, cn phn cn li gi l thp m b cm. phc v yu cu v ghi; truyn tn hiu vi deo, m ho c s dng trong cctrng hp sau.M ho s cp: Dng to tn hiu s studio .

M bo v sa sai: Tng kh nng chu ng ca tn hiu trong knh c nhiu.M truyn tuyn tnh : Tng kh nng truyn dn .

u tin tt c cc tn hiu video s c m ho s cp, sau m ho chuyn


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i (transcode) m s cp l m c s, m t hnh thnh m bo v, m s cp

c dng tn hiu nh phn lin tc 0 v1.

M c cu trc tuyt i. M c cu trc tng i .IV.3 Cc m s cp.

Cc m s cp ch yu c s dng m ho tn hiu truyn hnh x l s

nh c lng d, trong cc thit b t hp studio ca trung tm truyn hnh s.M s cp trong truyn hnh s l m ng u, c cu trc tuyt i. NRZ (Non

Return to Zero): khng tr li mc khng.RZ (Return to Zero ) : Tr li mc khng.

BiPh (Bi Phase ) : Hai pha.Bng t m ca m s cp cn phi tho mn iu kin qn- 1< N qn. Trong N lcc mc lng t ca tn hiu truyn hnh c m ho.iu kin ny dn n trng hp th nht l m s cp c th c d no y

,th hai l phn d ca t hp m lun lun nh hn mt na tng s mc m ho .Thng trong truyn hnh s, c s ca m s cp bng hai, ngha l m ny l mnh phn .Cc m s cp c phn thnh loi c trng s v loi khng c trng s bao gmcc m m bn cnh mi bc ca t hp m ca n c nhn bit mt h s trng sno .Chng III. Nn nh sI. Mc ch nn.

Vi k thut s ho truyn hnh, tc truyn di thng qu ln. Do vy i

hi rng knh truyn l rt ln. V d tn hiu video s thnh phn (s ho 8 bit-625 dng) c tc bit bng 216 Mbit/s. Di ph cn thit truyn tn hiu ny.

Trong studio truyn tn hiu bng cp, rc ri cht lng cao v vi khong cchngn, vic nn di tn ch mang tnh kinh t, nn vic truyn tn hiu c th thc hindc m khng cn nn. Xong s rt kh khn thm tr khng th htc hin dcvic truyn tn hiu video s qua v tinh vi rng di tn mt knh 27MHz hocqua h thng truyn hnh qung b trn mt t vi tiu chun 7-8 MHz cho mtknh truyn hnh tiu chun. Do vy nn video l cng on khng th thiu c

khc phc nhng kh khn v yu cu di bng tn cho php.II. Thc cht ca nn video s :

Bn cht ca nn video l qu trnh trong lng s liu (data) biu dinlng thng tin ca mt nh hoc nhiu nh c gim bt bng cch loi b nhngtn hiu d tha trong tin hiu video. Cc chui nh truyn hnh c nhiu phn tging nhau. Vy tn hiu truyn hnh c cha nhiu d liu d tha, ta c th b quam khng lm mt thng tin hnh nh. l qu trnh xo dng, xo mnh , vngnh tnh hoc chuyn ng rt chm, vng nh nn ging nhau hoc khc nhau rt t.

Thng th chuyn ng trong nh truyn hnh c th d bo, do ch cn truyncc thng tin chuyn ng. Cc phn t ln cn trong nh ging nhau. do ch cntruyn cc thng tin bin i. Cc h thng nn x dng c tnh ny ca tn hiu


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video v cc c trng ca mt ngi (km nhy vi sai s trong hnh nh c nhiuchi tit m cc phn t chuyn ng ).Qu trng sau nn l gin nh to li nhgc hoc mt xp x nh gc.

II.1 M hnh nn nh.

Tng u tin ca b m ho video, tn hiu video c trnh by di dngthun tin nn hiu qu nht. im ct yu l phi xc nh ci g c m ho.S biu din c th cha nhiu mu thng tin m t cc tn hiu hn chnh l bnthn tn hi, nhng hu ht cc thng tin quan trng ch tp trung trong mt phnnh ca s m t ny. Trong cch biu din hiu qu, ch c phn nh d liu l cnthit truyn cho vic ti to li tn hiu video.

H18.M hnh nn video


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Hot ng th hai ca b m ho l lng t ho, gip ri rc ho thng tin cbiu din. truyn tn hiu Video qua mt s knhHot ng th ba l gn t m. Cc t m ny l l mt chui cc bt dng biudin cc mc lng t ho. Cc qu trnh ny s ngc li trong b gii m Video.Mi hot ng c gng loi b phn t d tha trong tn hiu Video v li dng s

gii hn ca h thng nhn ca mt ngi, nh b i phn d tha, cc thng tinging nhau hoc c lin quan ging nhau s khng c truyn i. Nhng thng tinb i m khng nh hng n vic nhn cng s khng c truyn i.

II.2. d tha d liu.

Nn s liu l qu trnh gim lng s liu cn thit biu din cng mtlng thng tin cho trc. Cn phi phn bit gia s liu v thng tin. Thc t gias liu v thng tin khng ng nht vi nhau s liu (v do l tn hiu) ch l

phng tin truyn ti thng tin. Cng mt lng thng tin cho trc c th biudin bng cc lng s liu khc nhau, n bao gm s liu hoc t khng cho thng

tin thch hp ln xc nh bit. d tha s liu l trung tm trong nn ca nh s. d tha d liu, khng phil mt khi nim tru tng m l mt thc t c th nh lng c bng ton hc.

Nu r1v r2l lng s liu trong hai tp hp s liu cng c dng biu dinmt lng thng tin cho trcs th d tha s liu tng i ca tp hp s

Rd= 1- 1/Cnliu th nht so vi tp hp s liu th hai c th c nh ngha nh sau:

Trong Cn thng c gi l t s nn v Cn=r1/r2

Trong trng hp r1=r2th CN=1v RD=0, c ngha l so vi tp hp s liu th haith tp hp s liu th nht khng d tha. Khi r2


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Nhiu tn ( bao gm :d tha khng gian, d tha hnh hc, d tha trong nh) ct ra phn bit s ph thuc ny ca Pixel. Ta dng d tha Pixel ch tt ccc tn trn.

D gim d tha trong pixel ca mt nh, dy Pixel hai chu dng cho vic nhnv ni suy phi c bin i thnh mt dng c hiu qu hn. Trong cc phng

php nn anh ngi ta thng s dng phng php bin i Cosin ri rc (DCT) bin i Pixel t mim khnh gian sang mim tn s, bng cch ny s gim c d tha d liu trong Pixel min tn s cao.II.2.3 D tha tm sinh l

Bng trc quan cho thy, s th nhn cng sng ca mt ngi thay ich gii hn trong mt php vi nht nh. Hin tng ny sut pht t s tht l mtkhng p ng vi cng nhy ca cc thng tin nhn thy. Thng tin n gin ctm quan trng t hn thng tin khc trong vng nhn thy. Thng tin ny c gi l d tha tm sinh l nhn. N c th c loi b m khng nh hng ng kn cht lng nh.

Khc vi d tha m v d tha trong Pixel, d tha tm sinh l c linquan n nh hng, n quan trng ti vic lng t ho. iu c ngha l nhx mt khong cch rng, cc gi tr u vo ln mt s hu hn cc gi tr u ra. l ton t khng o ngc (mt thng tin). Cho kt qu nn s liu c tn hao.III.CC PHNG PHP NN

Cc h thng nn l s phi hp rt nhiu cc k thut s l nhm gim tc bt ca tn hiu s m m bo cht lng nh. C hai k thut nn l nn tn hao vnn khng tn hao.

III.1 Nn khng tn hao:Nn khng tn hao l qu trnh nn khng mt thng tin, cho php phc hi li

ng tn hiu ban u sau khi gii nn.

y l qua trnh m ho c tnh thun nghch. H s nn ph thuc vo chi tit nhc nn.H s nn ca phng php ny lun nh hn 2:1

Cc k thut nn khng mt thng tin bao gm :III.1.1 M ho vi di t m thay i (VLC).

Phng php ny cn c gi l m ho Huffman v m ho enfropy datrn tnh thng k ca tn hiu, kh nng sut hin ca cc gi tr bin trng hp

trong mt bc nh v thit lp mt t m ngn cho cc t m c tn sut hiu sutcao nht, v t m di cho cc gi tr cn li. Khi thc hin gii nn cc thit lp mtrng hp s c s dng to li gi tr tn hiu ban u. M ho v gii m

Huffman c th thc hin mt cch d dng bng cch s dng cc bng tm kim.III.1.2 M ho vi di ca t m ng (RLC).

Phng php ny da trn s lp li ca cng mt gi tr mu to ra cc mc bit biu din s bt u v kt thc ca gi tr c lp li. Ch c cc mu cgi tr khc khng mi c m ho. S mu c gi tr bng khng s c truyn idc theo cng dng qut. Cui cng, cc chui khng c to ra bng qu trnh gii

tng quan nh phng php DCT hay DPCM.III.1.3 S dng khong xo dng v mnh.

Vng thng tin xo c loi b khi dng tn hiu truyn i vng thng


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tin tch cc ca nh. Theo phng php ny thng tin xo dng v mnh s khngc ghi gi v truyn i. Chng c thay bng cc d liu ng b ngn hn tutheo ng dng.

III.2 Nn c tn hao:

Nn c tn hao chp nhn mt mt mt t thng tin gia tng hiu qu nn,

n rt thch hp vi ngun thng tin l hnh nh v m thanh. N cho t l nn nhcao c th truyn dn, pht sng. ng thi cng cho mt t l nn thch hp chox l v lu tr nh trong Studio.

Nn tn hao thc hin theo ba bc sau.

Bc1: Bin i tn hiu t min thi gian sang min tn s bng cch s dng ccthut ton bin i Cosin ri rc DCT. Bc ny thc hin vic gim d thaca Pixeltrong nh, tuy nhin qu trnh ny khng gy tn hao tn hiu.Bc 2: Thc hin lng t ho cc h s DCT,lm trn cc s liu vic mt mts liu xy ra giai don lm trn ny.

Bc 3: Nn s liu bin i v lm trn bng cch m ho Entropy, y dngcc m khng tn hao nh m Huffman, RLC...

IV.Cc loi m dng trong nn:IV.1 M RLC (Run-length coding)

RLC l loi m xy dng trn c s s dng s ln lp li ca cc im nh.RLC tch chui cc gi tr ging nhau v biu din nh l mt tng. Khi dn gi trny to li s ln biu din tng. K thut ny ch c th p dng cho cc chuiSympol tuyn tnh.

Do , khi p dng cho s liu nh hai chiu, hnh nh c tch thnh mt chui ccdng qut.Mt loi ci bin ca m RLC l m VLC (m c di thay i c) m nay dng biu din cc gi tr Sympolcng nh di chy. Cch thc hin l tch phn bxc sut ca cc di chy v cc gi tr Symbol. RLC khng thch hp trc tipcho cc nh t nhin c tng nh lin tc c m ho bng mt qu trnh s hotuyn tnh, v RLC phi nn tp s liu c bc chy tng i ln ging nhau, trongkhi nh hng c tng lin tc c tn s khng gian thp, vic thay i cc vngrng c lm y bng cc gi tr Pixel ging nhau l tng i nh. RLC t n skhng cho cc mc nn c ngha. RLC c dng kt hp vi cc k thut khcnh cc chun nn IPEG, MPEG s cho kt qu nn tt. RLC c dng cho cc hs lng t ho tt hn l dng trc tip cho s liu nh.

IV.2 M Shannon Fano.

M ny da trn xc sut xut hin ca nhng Symbol ngun bn trong mtlng thng tin. Phng php ny s dng nhng t m c di thay i m hocc Symbol ngun thng qua xc sut ca chng, vi nhng Symbol c xc sut xuthin cng ln th t m dng m ho chng cng ngn.

IV.3 M Huffman.M Hufman thuc loi entropy hoc m thng k. T tng chnh l dng m

VLC, s dng t bt m ho cc gi tr hay xy ra, v nhiu bit m ho cc gi


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tr t xy ra.T d tc bt s gim ng k.

Ni chung, m Huffman s t hiu xut thp nu xc sut xut hin cc phn

t gn nhau. Ngc li hiu sut cao nu xc sut xut hin cch xa nhau.Trn thc t m huffmanc pht trin trn mt tp nh, nhng sau c pdng trn cc nh khc nhau, mi nh c phn b xc sut Symbol ring ca n.

Do , Huffman khng cn ti u cho nh c bit no.

IV.4 M d on (DPCM )

Phng php m d on hay cn gi l iu xung m vi sai (DPCM). phng

php ny khng m ho bin thng tin mi mu, m ch m ho cc thng tin c

bin chnh lch gia mu cho v mu d bo. Do phn b chnh lch v bin im nh c th hnh chung xung quanh im khng. Nu da trn cc c

trng thng k, th s khc nhau ny l khng ln lm, do vy m ho n ch cngim mt s t bt l . Phng php m ho d on cn s dng c im ca mt

ngi v cho php dng c trng phi tuyn v lng t ho.Sau y l s m ho v gii m DPCM:

Nhm trnh cc li c th xut hin trong khi truyn, mt mu y c gii theo chu k nht nh, cho php cp nhp c cc gi tr chnh xc. M ho

DPCM cng s dng trn cc k thut d on v lng t ho thch nghi han

thin thm k thut nn ny.

IV.4.1 DPCM trong mnh (intsaframe DPCM).


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Tn hiu d bo c to t cc mu nm trong cng mt mnh, cc muc bin i c nm trn cng mt dng qut ( m gia cc Pixel) v cng vicc dng qut ln cn (m gia cc dng).Vic to tn hiu d bo ca DPCN trong mnh da trn mi lin kt gia cc imnh. Cc cng trnh nghin cu cho thy h s lin kt gim nhanh khi i xa im nhquan st theo chiu ngang (cc Pixel trn cng mt dng ). V theo chiu ng (ccPixel ca dng k nhau). Do khi to tn hiu d bo cn ch n mu tn hiu knhau.Tn hiu d bo c th l hm tuyn tnh hoc c th l hm phi tuyn i hi thit kmch phc tp hn o trong thc t khng dng cho tn hiu video.

IV.4.2 DPCM gia cc mnh.

tn hiu d bo c da trn c s cc mu cc mnh k nhau trc .Phng php DPCM gia cc mnh tn dng quan h cht ch gia cc mnh knhau ca nh v c trng ca mt (nhy mo vi nh tnh hn nh ng). Nghin

cu thng k v cu trc nh cho thy rng s khc nhau gia cc nh k nhau lkhng ln lm. to li mt nh trung thc ch cn truyn cc im nh lm bin

i khi phc li (ti pha thu).Tt c cc im nh cn li t mnh trc hc nhtrc trong b nh.

Phng php DPCM gia cc mnh thun li cho truyn hnh thoi .V tn hiutruyn hnh thoi c c im l nh chuyn ng t, tc chuyn ng chm, do vng nh rng, t thay i gia cc mnh k nhau.

Phng php c bn ca DPCM gia cc mnh l m ho trc tip Visai gia cc

mnh k nhau.Dc trng lng t l phi tuyn nn s chnh lch nh gia cc mc s c

khi phc vi chnh xc hn so vi mc chnh lch ln. iu khng nh vickhi phc mt cch chnh xc cc vng nh rng, chuyn ng chm ( m trn tt c cc mo rt d nhn bit ).

Ngc li, ti vng nh c nhiu chuyn ng, khi khi phc li s km chnhxchn v do c im ca mt ngi, ddooj phn gii ca nh c th thp hn.Cc loi DPCM thng dng:

IV.4.2.1 Intraframe DPCM.

y l phng php ly mu t phn nh chuyn ng, ch truyn cc phn nhchuyn ng v khi phc cc im nh cn li bng tr trung bnh cc nh ctruyn.IV.4.2.2 Phng php lm y c chn lc (Selective replenishment)

Phng php an cho cc mnh cn gi l phng php lm y c chn khi nhtruyn t chuyn ng v tc thp. Phng php ny da trn nguyn tc chtruyn phn im nh c chn mi mnh v nh c chiu sng lu.

IV.4.2.3 Phng php chia thnh nhng phn nh chuyn ng v tnh.

Phng php ny l s kt hp ca phng php lm y c chn lc v phngphp ly mu tng phn trong nh chuyn ng cng vi DPCM gia mnh vi dbo mt phn t. Mi nh c chia thnh phn t chuyn ng v phn t tnh, i


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vi phn t nh ng th s dng phng php ly mu tng phn.

IV.5 Phng php m chuyn v (transform coding).

i vi vic m ho ring r tng im mt s khng t c hiu qu bi v khngtn ht c mi quan h gia cc khi im trong nh s. Phng php m chuynv l mt cch c hiu qu trong vic m ho khi im thng qua bin i tuyn tnh

cc im ny thnh cc h s chuyn v v m ho cc h s chuyn v.

Trong h s PCM (tuyn tnh) v DPCM ngi ta cn c vo bin tn hiu thchin, cn trong m chuyn v th da vo vic chuyn i tn hiu t min thigian sang min tn s. y khng phi php bin i Fourier v n khng ph hp,m ngi ta dng php bin i tuyn tnh, phng php gm cc bc nh sau:- Chia nh thnh cc khi tiu nh vi kch thc nxn.

- Bin i tuyn tnh cc phn t (mu) ca tn hiu mi tiu nh.

- M ho cc phn t ca tn hiu.

H thng m ho v gii m chuyn v


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h22. Gii M

Trong m chuyn v, bc u tin l phi chn mt chuyn ithch hp gim si lp gia cc im trong khi mtcch hiu qu. Mc d bn thn qu trnhchuyn i ny khng lm gim tc bit i cht no nhng n c hiu quatrongvic gim d liu trong qu trnh lng t ho. Hay ni cch khc, qu trnh chuyni thnh m chuyn v khng h xy ra nn d liu m ch l bc chun b cho vicgim d liu trong qu trnh lng t ho. Sau khi chn c bin i trc giao th

bc quan trng nht l xc nh bit ch nh v thit k h thnglng t ho cho

cc h s ny tan b qu trnh nn d liuc thc hin ti y. Bc cuicng l s dng m entropy gim tc d liu.

Mc ch ca vic chia nh thnh cc nh con nxn l tch lin kt cc Pixel catng nh con hoc gi cng nhiu thng tin v mt s t cc bin i.Sau trng thi lng t ho tch c chn lc hoc lng t ho th hn cc h smang tin t nht, cc h s ny t nh hng n cht lng nh con c khi phc.Qu trnh m ho xc nh cc h s lng t ho c thc hin bng m VLCChn chuyn v (bin i): Cc h thng m chuyn v (bin i) tn c s bin ikarhuman Loeve (KLT), DFT, DTC, Walsh-hadamard (WHT).Vic chn mt chuyn

v c th cho mt ng dng nht nh ph thuc vo mc sai s khi phc ca n vc th tnh bng my tnh. C th nn trong khi lng t ho cc h s bin i(nhng ngai thi gian chuyn v) Hu ht cc h thng m chuyn v trn thc tu da trn c s DCT, n cho php phi hp tt gia kh nng gi thng tin v

phc tp tnh ton.Mt c tnh quan trng ca DCT so vi cc bin i sin khc l: Nu nh bin iDFT s dn n lin kt khng lin tc trong ni dung cn chuyn v cc thnh phntn s cao v nu cc h s ny c trung chuyn, lng t ho th s gy ra hintng Gibbs v gy ra sai s. Cn DCT khng to ra s ri rc trong lin kt, do n hn ch c sai s do Gibbs gy ra.

Phng php ny tp chung vo mt s cc h s chuyn v m khng phi cc imnh ca nh gc v lng thng tin ch trong mt s t cc h s chuyn v nh vys bt dng cho qu trnh chuyn v s t i.


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Mt l do na l do h thng th gic ca con ngi khng nhn bit c han tancc chi tit ca nh khi cc chi tit bin i nhanh so vi cc chi tit bin ichm, do vy m ho cc h s chuyn v tn s cao ta ch cn mt s t bit m

cht lng hnh nh s cao.Trong h chuyn v hai chiu cho cc nh s, da trn c s tng quan gia cc mutrn dng hnh. Trc tin mt khi c chia thnh nhiu khi hnh ch nht

vi kch thc pxq. Sau cc khi ny c chuyn v v cc h s thu c sauqu trnh chuyn v c lng t ho v m ho. Phng php chuyn v xut hinmo do vic chia nh thnh cc khi nh con.V. Nn trong nh.

1. Nguyn l nn trong nh.

H23. S nguyn l qu trnh nn trong nh

Nn trong nh l loi nn nhm lm gim bt thng tin d tha trong min khnggian. Nn trong nh s dng c hai qu trnh nn c tn hao v nn khng tn hao

gim bt d liu trong mt nh. Qu trnh ny khng s dng ca cc nh trc

v sau nh ang xt.

Thut ng nh cn c hiu mt cch chnh xc, bi v trong k thut nn nh chophp s dng hoc mnh (fied) hoc nh (frame) nh mt nh gc. Nu k thut nndng mnh th nn trong nh s to ra hai nh trong mi nh.

2.Tin x l

Trc khi thc hin bin i DCT, c nh c chia thnh cc khi ln ring bitkhng trng nhau(khi MB).Mi MD bao gm bn block cc mu tn hiu chi(Y)v2:4 hoc tm block cc mu tn hiu s mu(CR, CB). S cc block phthuc vo cc chun Video.


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a.Cu trc blocok tn hiu chi (qut lin tuc)

b.Cu trc blocok tn hiu chi (qut xen k)

Tt c cc blok c cng kch thc v mi blok l mt ma trn im nh 8x8 c

ly t mt nh mn hnh theo chiu t tri sang phi, t trn xung di. Kch thcblock l 8x8 c chn bi hai l do sau:

- Th nht: l vic nghin cc ch ra rng hm hip phng sai suy gim rtnhanh khi khong cch t pixel m hm hip phng sai c nh ngha vtqu 8. Chnh v vy m phng php nn s dng loi b cc thng tin d tha vkhng gian khng cn quan tm ti cc khi pixel c kch thc ln hn 8x8.

- Th hai: l s tin li cho vic tnh ton v thit k mch cng. Ni chung, c

mc nn ln phc tp v tnh ton s tng nu kch thc block tng.

VD: v vic chia thnh cc block ca hnh i vi h PAL. Phn tch cc ca

tn hiu Video i vi phn gii 576x720 s c chia thnh 72x92 block. V nh

vy s c 36x45 MB nu tiu chun ly mu l 4:2:0 hoc 4:1:1.Cu trc ca MBcng ph thuc vo loi qut nh. Nu qut lin tc th cc block bao gm cc mu tcc dng lin tc (lc ny l nn theo nh frame) hnh sau. Ngc li trong trng

4 50 1

2 3

0 12 3

0 1

2 3

4 5

6 7

5 7

9 11

4 8

6 10


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hp qut sen k, trong mt block, ch cc mu ca mt na nh (nn theo mnh-fised). Tm li, vic chia hnh nh thnh cc nh con(block,MB) s thc s c ngha tip theo3. Bin bi cosin ri rc(DCT)

Cng on u tin ca hu ht cc qu trnh nn l xc nh cc thng tin dtha trong min khng gian ca mt mnh hoc mt nh ca tn hiu Video.Nn

khng gian c thc hin bi php bin i DCT(Discrete Cosine Transfrom). DCTbin i d liu di dng bin thnh d liu tn s. Mc ch ca qu trnh bini l tch lin kt ca tng nh con, hoc gi cng nhiu nng lng ca nh convo mt phn nh cc h s hm truyn. Vic m ho v truyn ch thc hin i vicc hius nng lng ny, v c th cho kt qu tt khi to li tn hiu Video c chtlng cao. DCT tr thnh tiu chun quc t cho cc h thng m chuyn v bin c c tnh gi nng lng tt, cho kt qu l s thc v c thut ton nhanh thc hin chng.

Cc php tnh DCT c thc hin trong phm vi cc khi 8x8 mu tn hiu chi Yv cc khi tng ng ca tn hiu mu. Vic chia hnh nh thnh cc block cthc hin khi tin x l. Hiu qu ca vic chia ny rt d thy v l mt trongcc phm quan trng ca m ho c cht lng cao.

Nu tnh ton DCT trn tan b frame th ta xem tan b frame c d tha lnh nhau. Nh c tnh thay i ca cc nh khc nhau v cc phn khc nhau cacng mt nh, ta c th ci thin mt cch ng k vic m ho nu bit tn dng.

V vy s dng cc c tnh thay i ca cc phn t d tha trn c s m rng

khng gian cu nh, DCT c tnh trn cc MB v mi MB c s l ring bit. hiu bit ng dng ca DCT trong nn nh, ta tm hiu thut ton bin i cosinri rc. DCT l ton t dng tnh cc thnh phn tn s ca mt tn hiu c lymu ti mt tc ly mu.

4. Lng t ho.

Bc tip theo ca qu trnh nn l lng t ho cc h s F(u, v) sao chogim c s lng bit cn thit. V cc h s c gi tr khc nhau, cho nn cc h sring c th tnh bng cc phng php khc nhau. Cc h s tng ng vi tn s

thp c gi tr ln hn, v nh vy n cha phn nng chnh ca tn hiu, do philng t ho vi chnh xc cao nht, v n biu hin chi trung bnh ca tngkhi phn t nh.


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Hnh25

Bt k mt s sai st no trong qu trnh lng t ho, h s mt chiu u c kh

nng nhn bit d dng, v n lm thay i chi trung bnh ca khi. Ngc li

vi cc h s tng ng vi tn s cao v c gi tr nh, th biu hin bng tp cc

gi tr nh hn hn cc gi tr cho php. Qu trnh ny c th thc hin c bngcho nhng khong cch gia cc bc lng t ho thay i theo h s.

Lng t ho c thc hin bng vic chia cc h s F(u,v) cho cc h s v trtng ng trong bnh lng t Q(u,v) biu din s ln nh hn cc gi tr cho

php ca h s DCT. Cc h s c tn s thp c chia cho cc gi tr nh, cc h sng vi tn s cao c chia cho cc gi tr ln hn.Sau cc h s c lm trn(b i cc phn thp phn )

Cc gi tr F(u,v) s c m ho trong cc cng on tip theo. Cn phi xc nh ltrong qu trnh lng t c trng s c xy ra mt thng tin, gy tn hao.

y l bc gy tn hao duy nht trong k thut nn. Mc tn hao ph thuc vogi tr cc h s trn bng lng t. Nhiu lng t i vi tn hiu mu kh nhnthy hn i vi tn hiu chi, cho nn c th thc hin lng t ho thng tin hiumu.

Nh vy, khi lng t DCT ng vai tr quan trng trong qu trnh lng t ho khi

thit k h thng nn Video v n nh hng trc tip n vic khi phc cht lnghnh nh tt hay xu. Vic dng cc m bin sao cho thu c kt qu tt tu thucvo thnh phn tn s bin i chi tit nh sng tng vungf trong min khng gian


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nh. Cc nh cng chi tit th h s thnh phn tn s cao cng ln, nu h s trongcc bng lng t tng ng qu thp c th dn n b m. Mt thng tin hi tipv b m cho php iu khin mt h s cn bng, qua iu khin ti u trngthi ca b m. H s cn bng ny ch a vo cc thnh phn AC m thi. H scn bng l mt hng s trong mt cu trc khi c bn cha ng hai khi mu vmt s thay i v khi chi ph thuc vo cu trc nh ban u.

5.M ho entropy.

lng t ho v gn t m c s tng quan gn gi m khng cn phi tch bit

r rng. Ni mt cch khc, lin kt ti u ca lng t ho. Cc gi tr lng

t ho c th ch biu din nh cc t m c tc di c nh hay ng u, tc lcc gi tr lng t ho biu din bng cng mt s bit. Tuy nhin hiu qu ca vicm ho khng cao. ci tin hiu qu ngi ta dng m ho entropy. M hoentropy dng nhng c tnh thng k ca tn hiu c m ho.M ho entropy c hai vn c t ra.

- Th nht :M ho entropy lm tng phc tp v yu cu b nh ln hnso vi m di c nh.

- Th hai : m ho entropy gn lin vi tnh khng n nh ca tn hiuVideo s lm tc bit thay i theo thi gian. Do cn c c cu iu khin b

m khi m ho gun tc bit bin i c ghp vi knh tc khng i.

VI. Nn lin nh.

1. M hnh.

Mt tnh cht ca tn hiu Video l cha thng tin d tha trong min thi gian.

C ngha l, trong mt chui nh lin tc, lng thng tin cha trong mi nh s thayi rt t t nh ny sang nh khc. Tnh ton s dch chuyn v tr ca ni dung hnhnh l mt phn rt quan trng trong k thut nn lin nh. M hnh nnlin nh nh sau:

Hnh26.

Mt chui Video l mt chui nh tnh c hin ra vi tc nhanh s cho cmgic chuyn ng lin tc. Mc d cc frame c s khc nhau, cn thit phi c mttc frame cao y c cm gic chuyn ng thc s. T to ra nhiu d tha tn thi gia cc frame k nhau, s b chuyn ng chnh l loi b phnd tha ny. Sau qu trnh b chuyn ng, tng hiu qu nn cn s dng k

thut nn trong nh s l d tha trong khng gian trong phn d tha ca bchuyn ng.


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2. Xp x v b chuyn ng.

Nhiu thay i v cng nh sng t frame k tip l do chuyn ng ca itng. Trong m b chuyn ng, frame hin ti c d bo t frame trc bngcch xp x chuyn ng gia hai frame v b chuyn ng . S khc nhau giaframe hin ti v frame trc gi l phn d tha ca b chuyn ng v phn dtha ny s c m ho.

i vi mt chui Video bnh thng, c trng v nng lng ca phn d thathp hn rt nhiu so nng lng trong tn hiu Video gc do loi b thnh phn dtha tm thi. M ho phn d tha thay v m ho Video gip m bo thng tin dtha tm thi khng b m ho lp li.

Nh vy, vic xc nh phn nh rng l xp x chuyn ng. Qu trnh khi

phc mt nh bng cch dng cc phn t nh trc cng vi thng tin v chuynng chnh l b chuyn ng. S dnh gi chuyn ng c th l ton frame. thc hin ti u, chia mi frame thnh cc khi (8x8 pixel) sau mi nh gi

chuyn ng cho tng khi.

Vic nh gi chuyn ng frame s gy ra hai vn sau:

- Thi gian dng theo di mt vng nh rng ca nh cho vector chuyn ngc tnh ton.

- Cc khi chuyn ng dn n vic xc nh ci g t vo khng gian trng(do khi chuyn ng ).

S dng xp x v b chuyn ng l thay th hai yu cu trong h thng m ha/gii m. u tin b gii m phi lu nh trc trong khi to nh tip theo. Sau ,

b m ho phi to li mi nh sau khi m ho n d bo cho b gii m to nhnh th no. iu ny cn thit v b gii m khng c bt k mt nh gc no c

th to li khi b chuyn ng.Mt phng php d on tm ra cc chi tit nh thay th gia hai khung hnhnhn nhau v to ra mt vector chuyn ng v tr ca chi tit nh ny trong khunghnh tng ng. Theo, vector chuyn ng s phi hp vi tt c cc khic nn trong khung hnh trc m khi cacs im nh ny c lp li ti mt

v tr mi.

H27. Vector chuyn ng hai khung hnh lin nhau


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C nhiu phng php khc nhau xc nh vector thay th, mt trong s ccphng php ny c tn gi l phi hp cc khi (block matching). Khi s liuim nh c la chn, gi l khi tham chiu, trong khung hnh hin ti chuyn

ng trong khung hnh trc . Cc gi tr DCT tham chiu c so snh vi ccgi tr 8x8 im trong vng tm kim tm ra khi thch hp nht, tng ng khi

s sai khc l nh nht. Khi vector xc nh khong cch ca v tr tham chiuv v tr phi hp tm thy to ra. Thng tin s liu v vector chuyn ngc truyn ti cng vi khi h s DCT sai lch.

gim qu trnh tnh ton vector chuyn ng, phn gii ca nh c th cgim xung theo c hai chiu ngang v chiu ng. Bng cch ny c th gim s btcn x l v d on cc phn chnh c thay th trong khung hnh.

V d mt nh vi phn gii y l 720x480 c th gim n mc 360x240.

nh vi phn gii thp c th dng cho vng d on ln hn. u tin, mt d

on chuyn ng gn ng s c tin hnh trn cc nh c phn gii thp ny.Sau , mt php d on vector chuyn ng chnh xc s thc hin tnh tonv tr thay th chnh xc ca i tng gia hai khung hnh. Qu trnh d bo s

thc hin qua nhiu bc thu c d bo chnh xc cui cng.

i vi cc i tng chuyn ng nh c th b qua trong giai on d onchuyn ng gn ng, do vector d on s mang sai s. Trng hp ny s sdng cc khi nh hn. Vi mt vng thay th c kch thc ln, sai s trong qutrnh phi hp s tr nn ln hn gia cc khi c cng mc xm song khng c linh v chuyn ng. Hn na, nhiu nhng kiu chuyn ng trong bc nh c

th to ra s xung t trong vng tm kim. gii quyt vn ny c s phn chiatrong vic phi hp cc khi.

3. Tc truyn sau khi nn.

Ta c mi quan h gia tc truyn C bng tn knh truyn W. WC (W:MHz; C:Mbit/s)Di y thng k tc truyn ca cc loi nh.

- nh tnh:1,2 - 9,6 kbit/s.

- nh chuyn ng chm :12-40 kbit/s

- Truyn hnh thoi: 58-2000kbit/s.- Truyn hnh en trng: 70-108 Mb/s.

- Truyn hnh mu: 216Mb/s- Truyn hnh HTV: 1,1- 2,3Gb/s

Sau khi s dng cc thut ton nn Video, th tc truyn ca tn hiu hnh cgim i nh k, c ngha l rng di thng gim i.

- C=2-13Mb/s

- Di thng W: 1,5MHz - 9MHz


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Nh vy do u im cho nn vic truyn tn hiu truyn hnh s c nn Videohin ang c s dng rng ri cho hiu qu kinh t v k thut cao. Ct lng

ng truyn cao, tic kim bng tn.VII. Cc chun MPEG.

1. Gii thiu chung v chun MPEG.

Chun MPEG (Moving Picture expert Groug) l chui Video vi mc ch lm ho tn hiu hnh nh v m thanh cho DSM(Digital storage Media) tc t 1,5n 50Mbit/sv c bit n nh l MPEG-1, MPEG-2, MPEG-4,...Cc chunMPEG tin ti ti u ho cho cc ng dng videong v cc c im ca n cng

bao gm mt thut ton cho vic nn d liu Audio vi t l l 5:1 cho ti 10:1.Trong chun MPEG, ngi ta nh ngha cc loi nh khc nhau cho php s linh

hot cn nhc gia hiu qu m ho v truy nhp ngu nhin. Cc loi nh nhsau:

1.1 nh loi I (Intra-picture).

L nh c m ho ring. nh loi I c cha ng d liu ti to li tanb hnh nh v chng c to thnh bng thng tin ca ch mt nh. nh I cho phptruy cp ngu nhin, tuy nhn t c t l nn thp nht.

1.2. nh loi P(Predicter-picture).

L nh m ho c b chuyn ng t nh I hoc nh P pha trc (nh cd on trc). nh P cung cp cc h s nn cao hn nh I

1.3. nh loi B(Bidiretional Predcited-picture)

L nh c m ho s dng b chuyn ng t nh I v nh pha trc vpha sau(nh d on hai chiu). nh B c t l nn cao nht.

1.4 Nhm nh (GOP).

i vi chun MPEG, cht lng nh khng nhng ph thuc vo t l nntrong tng khun hnh m cn ph thuc vo chiu di ca nhm nh. Nhm nh(Group of picture) l mt khi nim c bn ca MPEG. GOP l n v mang thngtin c lp ca MPEG.

Cng ngh MPEG s dng ba loi nh I, P, B. Trong nh P, B khng phi l mtnh han chnh, m ch cha thng tin v s khc bit gia nh v nh trcn(i vi nh P), hay s khc bit vi c nh trc v nh sau n (i vi nh B). c mt khun hnh han chnh, nh P v nh B cn c d liu t cc nh ln cn,v vy MPEG a ra khi nim GOP. Mi GOP bt buc phi bt u bng mtnh han chnh I v tip sau l mt lot cc nh P v B. Nhm nh c thm(Open) hoc ng (closed).

Nhm nh m lun bt u bng mt nh I v kt thc mt nh trc nh I tip

theo, c ngha l nh cui cng ca GOP dng lm nh u tin ca GOP tip theo


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lm nh chun.

H28. Cu trc GOP m H29.Cu trc GOP ng

i vi cu trc khp kn, vic d on nh khng s dng thng tin ca GOP khc.Trong trng hp ny theo quy nh, nh cui cng ca mt GOP bao gi cng lnh P. Nhm nh ny c xc nh bi hai thng s m v n. Thng s m xc nhkhung hnh P v khung hnh B xut hin gia hai khung hnh I gn nhau nht. S nxc nh s khung B gia hai khung P.

T l nn video ca MPEG ph thuc rt nhiu vo di ca GOP. Tuy nhin GOPdi thng gy kh khn cho qu trnh tua, nh v , sa li... Do tu thuc votng khu (sn xut, dng, truyn dn, pht sng...) m ta chn di GOP thchhp. Trong sn xut hu k, nu yu cu truy cp ngu nhin v bt c nh no, iu c nghi l yu cu truy cp chnh xc n tnh nh , GOP khi ch c nh loiI, trng hp ny s cho t l nn rt thp. tng t l nn, s lng nh P v B

phi tng ln, lc ny s khng cho php vic s dng hnh cng nh lm k xo trnchui nh . Trong trng hp ny GOP c th bao gm 12 nh.1.5 Cu trc dng bit MPEG video.


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Cu trc dng bit video bao gm 6 lp:

a. Khi :khi 8x8 cc im nh tn hiu chi v tn hiu mu dng cho phngphp

nn DCt.

H30.Kin trc dng bt vi deo

b. Cu trc khi (macroblock):Mi cu trc khi l mt nhm cc khi tngng

vi lng thng tin cha ng cho kch thc 16x6 im trn nh. Cu trc khicng xc nh lng thng tin cha trong s thay i tu theo cu trc mu cs dng. Thng tin u tin trong cu trc khi mang dng ca n ( l cu trc Y vCr Cb) v cc vector b chuyn ng tng ng.

c. Mng (Slice): Mng bao gm mt vi cu trc khi k nhau kch thc ln


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nht ca mng c th gm tan b bc nh v kch thc nh nht ca mng l mtcu trc khi. Thng tin u ca mng cha ng v tr ca mng trong tan b nhv h s cn bng lng t. Kch thc thng tin u ca mng c xc nh bng

s li cho php xut hin trong mng i vi mt ng dng nht nh theo , b giim c th b qua cc mng c nhiu li, xc ng tn hiu qu ca phng

php nn nh, theo h s cn bng lng t c th c iu chnh thng

xuyn vi vic s dng mng c kichs thc nh hn. H s DC tham chiu (dngtrong m ho DPCM) s c so snh chun ti u mi mng.d. nh: Lp nh cho php b gii m xc nh loi nh ca nh c m ho lnh I, P hay B. Thng tin u dng ch th t truyn khung b gii m c th

sp xp cc nh theo mt th t ng.

Thng tin u ca nh cn cha cc thng tin ng b, phn gii v phm vi cavector chuyn ng.

e. Nhm nh: Nhm nh l mt t hp rt nhiu cc khung I, P v B. Cu trcca nhm nh c xc nh bi hai tham s m v n. Mi nhm nh bt u bngkhung I v xc ng im bt u tm kim v bin tp. Thng tin gm 25 btcha m nh thi v iu khin.

f. on Video: on video bao gm thng tin u, mt s nhm nh v thng

tin kt thc on. Thng tin u ca on video cha kch thc mi chiu ca nh,

kch thc im nh, tc bit ca dng video s, tn s nh v b m ti thiucn c. on video thng tin u to thnh mt dng bt c m ho gi l dng

c bn (Elementary stream).

1.6 Nguyn l nn dng bit.

Vi cc loi nh ni trn, vic m ho theo loi no l tu thuc vo nh

thit k. Tuy nhin cu trc ca b m ho MPEG c th theo s sau:

- Nguyn tc hot ng ca mch m ho MPEG

Cch hot ng ca b m ho ph thuc vo loi hnh nh m ho ti thi

im ang xt. Nn MPEG l s kt hp gia nn trong nh v nn lin nh. Dng

thc u vo l Rec-601 4:2:2 hoc 4:2:0 c nn lin nh trc to ra nh khc

bit u ra b cng. nh ny sau li c nn trong nh qua cc bc: Bin i

DCT , lng t ho, m ho. Cui cng nh ny c trn vi

vector chuyn ng a n b khuch i m s thu c nh nn.


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H31. S khi caqu trnhm ho MPEG

Tc bit ca tn hiu video c nn khng c nh, ph thuc vo ni dungnh anh xt. Ngc li, ti u ra ca b m ho, dng bit phi c nh xc

nh tc cho dung lng knh truyn. Do , ti u ra ca b m ho phi c

b nh m ln. B m ho phi kim tra trng thy y ca b nh m khi

s liu trong b nh m gn bng dung lng cc i, th cc h s bin i DCTc lng t ho t chnh xc hn. Trong trng hp ngc li, c nghi l b nh

m cha s liu qu t, th vic lng t ho cc h s s tng ln.Qu trnh gii m theo l thuyt l qu trnh ngc li vi qu trnh m ho trn.

2. Tiu chun MPEG-1

L tiu chun nn mt nh ng c kch thc 320x240 v tc bt cn t mt


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Mbit/s n 1,5 Mbit/s dng cho ghi hnh trn bng t v a quang(Cd) ng thitruyn dn trong cc mng (v d mng my tnh).2.1 Tiu chun MPEG-2

MPEG-2 hng ti cc ng dng rng ri hn v c tc bit cao hn MPEG-1, baogm cc ng dng DSM (lu tr s) cc h thng TV hin ti nh (PAL,NTSC,SECAM) cp, thu lng tin tc in t, truyn hnh trc tip qua v tinh,EDTV (truyn hnh m rng ), HDTM (truyn hnh phn gii cao)...

CHNG III.

AUDIO S V CC TIU CHUN NN AUDIO S

I. Khi nim m thanh.

m thanh l do vt th rung ng, pht ra ting v lan truyn i trong khng kh.S d tai ta nghe c nh c mng nh. Mng nh ni lin vi h thnh thn kinh.

m thanh cng truyn lan c trong cc cht kh, cht lng, cht rn... nhng khngtruyn lan c trong chn khng.Mt s cht truyn m rt km, thng l loi mm, xp nh bng, da, c kh. Cccht ny gi l cht ht m, c dng lm lt tng cc rp ht, cc phngcch m... ht m, gim ting vang.

Vn tc truyn lan ca m thanh ph thuc vo cht truyn m. V d nh khng kh

l 340m/s, trong nc l 1480m/s, trong st l 5000m/s.Tn s ca m n l s ln giao ng ca khng kh truyn m trong mt giy

ng h. Tai ngi c th nghe thytn s t khong 16Hz n 20.000Hz.

Di tn t 16Hz n 20.000hz gi l tn s m thanh (hay m tn)

Di tn s di 16Hz gi l h m.

Di tn trn 20.000Hz gi l siu m.II. Pht tn hiu m thanh.

II.1.1 S khi my pht tn hiu m thanh.


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H32. S khi my pht

II.1.2 Chc nng tng khi.

1.Khi ca sng: C th l mt tng hoc mt s tng c kt cu phc tp. Nhim

v ca n l to ra dao ng in tn s gc cung cp cho cc tn s sau. V vygoi l ch sng.

2. Khi trung gian : C th l tng khuch i tng in p v cng sut t sngch a sang. Ty theo yu cu ca mi my pht m tng trung gian c thl cc tng m, nhn hoc chia. Tng m va khuch i va cch ly nhhng ca tng sau i vi ch sng, gi cho ch sng n nh. Tng nhn hoc chia tng tn s hoc gim tn s hai ba ln...So vi tn s ch sng a sangtu theo yu cu ca my pht.

m bo cho yu cu cung cp cho cc khi cng xut trc khi ra anten, trongkhi trung gian c th c thm nmt vi tng khuch i in p v cng xut cao tntu theo tng my.3. Khi cng xut : L tng khuch i cng xut m bo c yu cu cngxut pht ra anten.4. Anten: C nhim v bin dao ng in cao tn thnh sng in t truyn lan

ra khng gian, tu theo my pht v yu cu thng tin m thit b anten c thn gin hay phc tp, c th bc x sng in t c hng hoc khng hng.5. H thng fidow truyn dn nng lng cao tn u ra my n anten.6. Khi iu ch : Trong my pht thanh thng c tin tng m v nn, cc tng


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khuch i m tn v thit b iu ch.7. Khi ngun: Thng l tp hp cc loi chnh lu v cc thit b cung cpin cho tng my pht.

8. Khi iu khin: Dng iu khin my hot ng gi an tan cho ngi khaithc v cho thit b.

II.2. Su ch tiu cht lng cho my pht tn hiu m thanh.II.2.1 n nh tn s.

L mt ch tiu rt nghim ngt i vi my pht. Bn my thu ch c th thu

c thng tin lin tc v tt khi tn s bn pht khng x dch ra gii hn cho php.Do , tn s my pht phi m bo gii hn n nh cho php VD my pht tns 7MHz c php x dch khng qu 3.10-6. n nh tn s do khi ch sng

quyt nh l ch yu.II.2.2 Mo tn s:

L mc khuch i khng ng u i vi cc tn s c cc tn hiu c ch cnpht i, lm tng quan v mc ca cc tn s m thanh trong ni dung tintc khng cn trung thc na.

II.2.3 Mo phi tuyn.

Chnh l mo dng ca tn hiu hay cn gi l mo khng ng thng. Tn hiu cntruyn i l hnh sin nhng qua my pht sng hi nn b bin dng i khng cn l

hnh sin na mo phi tuyn to ln th m thanh s b nh, r..Mo phi tuyn cng t th m thanh cng trung thc. Mo phi tuyn ch yu do

ch cng tc ca tng khuch i tn hiu, iu ch, khuch i dao ng

iu ch quyt nh.II.2.4 su iu ch.

Cn gi l h iu ch ch tiu rt quan trng trong cc my pht iu ch bin. N l t s gia bin in p tn hiu vi in p dao ng cao tn. Trong cc

my pht thanh iu ch bin th su iu ch t trung bnh l: 70% n80%.

II.2.5 Mc bc x sng hi.L sng c tn s gp hai ba ln tn s cng tc ca my pht. Ngi ta phi hn ch

bc x sng hi ca my pht, nht l my pht do c cng xut ln. V khi c snghi pht ra s lm gim hiu xut ca my pht v gy ra can nhiu cho cci khc, nu sng hi trng tn s hoc ngay k tn s cng tc ca i .


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II.2.6 Mc tp m v ting .

L nhng ting n trong my pht to ra, s can nhiu n tn hiu c ch khi mc tp

m v ting ln c th khng th nhn bit c ni dung tin tc na. Mc tp mv ting c so snh vi mc tn hiu c ch. n nh tn s, mo tn s, mo phi tuyn, su iu ch, mc bc x sng

hi mc tp m v ting l nhng ch tiu c bn i vi my pht thanh sng ditrung gn.II.3 Nguyn l ghi m.

II.3.1 Cc phng php ghi m

i vi tn hiu m thanh tng t c cc phng php ghi truyn thng sau:

1. Ghi m c gii:Dng thit b c gii khc nhng tn hiu m thanh thnh dng cc rnh vng trntrn a nha. Khi cn pht li m thanh trn a ghi, th cho kim a ht chuyn ngtrn nhng rnh vng ng dng trong a ht.

2. Ghi m quang hc:

L phng php dng mirco v b iu ch quang a m thanh cn ghi vonhng phin nha cm quang. Ri em phin nha nh hnh ghi m, khng chnh sng ca n quang hc chiu ti, pht ra tn hiu ban u. Phng php ny

ng dng trong in nh.3. Ghi m t:

L phng php dng dng in m tn tc ng ln bng t li t d trn

bng t theo quy lut ca dng in m tn. Lc pht li th nhng mc t d trnbng qua u t c li bin thnh dng in m tn. Phng php ny ng dngtrong truyn thanh v i sng.II.3.2 Cc ch tiu cht lng ca my ghi m.

1. Tc chuyn bng nh dng:

l tc chuyn ng danh nh ca bng t chy qua u t. Tc chuyn

bng tnh theo cm/s. My ghi m c cht lng cng cao th tc chuyn bngcng ln. Thng l 76,2cm/s, 38cm/s, 9,53cm/s, 4,76cm/s.

Nu tc tng hay chm qu mc th s pht sinh ra mo tn s, nhanh qu th tingnghe eo o chm qu th ting nghe ...Khi c bng my khc th tc chuyn

bng sai lch khng qu 0,2% so vi tc khi ghi.2. Mc sai iu:

L mo do tc chuyn bng khng u trong khi ghi hoc trong khi c bng.

3.Di tn s cng tc:

Cc my ghi m c cht lng cao bao gi cng c di tn cng tc rt rng. Tc


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nhanh ca di tn s rng hn khi dng tc chm. V d: ng vi19,05cm/sditn cng tc l 4012.000Hz vi tc 9,53cm/s c di tn s cng tc l6010.000Hz

4.Mo tn s:Do cc nguyn nhn sau Khi ghi hay khi c, tc chuyn bng khng n nh.

Tc c khng cng vi tc ghi.

B khuch i khng khuch i ng u c di tn s cng tc.

Cc u t c kt cu han chnh, bng t su.

mo tn s ca my ghi m ph thuc vo cp tuyn tn s ca h thng ghi t

v mc hiu chnh tn s ca b khuch i.

5. Mo khng ng thngCa my ghi m ph thuc vo mo khng ng thng ca mo ghi t v

ca phn khuch i tn hiu me khng ng thng ca h thng ghi t gy

ra do tng quan khng ng thng gia lng cm ng t d v tr s dng in

u t ghi.

Mo khng ng thng sinh ra do nhiu nguyn nhn- Do cc ng cong t ho ca bng t.

- Do c tuyn, ch lm vic ca tranzitor c sai lch

- Do cc u t v bin p.6. Cng xut danh nh.

L cng xut m tn ca b khuch i c, ng vi mo khng ng thng chophp cc my chy pin thng c cng xut b hn my chy in, my chypin c cng xut vi trm mili ot, my chy in mt vi ot.

7. nhy u vo:

L in p u vo b khuch i ghi m bo mc ghi ln nht trn bng t.

8.Di ng:

Di ng l t s gia mc tn hiu ghi v c ln nht ca mc tn hiu ghi v cnh nht. Di ng ph thuc vo tnh cht ca bng t v mc tpm.

II.3.3 Nhc im ca phng php ghi tn hiu m thanh tng t

. Do mo phi tuyn s d l do ghi m da trn c s ca vic bin tn hiu t lvi mt i lng vt l no ca vt lu ghi( t d trn a, rng rnh ghi trna, vt ghi trn a...).

S hn ch ca t s tn hiu trn tp m. Do vy lm mt i s phong ph ca m

thanh trong t nhin.

khc phc nhng nhc im ny ngi ta chuyn sang ghi m bng k


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thut s thay bng v ghi m tng t, ghi m s chuyn t mc tn hiu sang m nhphn ghi theo chui ca cc con s 0 v 1 do vy ln b ca tn hiu cnghi s khng cn cn tr g na.

III. Khi nim c bn ca audio s.Vo u thp nin 80 cc thit b audio s dn dn thay th v chim lnh ccaudio tng t trong sn xut v pht sng, u im ni bt ca audio s l ghi ms nhiu ln m cht lng khng ghi gim, mo tn hiu mt cc l tng

0,01%, di ng m thanh ln gn mc t nhin(>90dP), vic tm kim d liunhanh chng, lu tr s v cc h thng sn xut chng trnh audio s da trn cs my tnh t ra rt hiu qu. Cng ngh s cho php ghi, x l, truyn dn phtsng v thu sng han tan trong mi trng s.

Mt tiu chun audio s ra i vi s lin kt ca hai hip hi, hip hi k thutaudio AES (Audio Engineeting Society)V hip hi truyn thanh truyn hnh Chuu EBU (european Broadcasting Union) xy dng cho nn tng pht trin cathit b ghi m v cc thit b ti Studio, ni x l tn hiu v phn phi han tans.

Thit b audio s c tn hiu vo ra tng t dng thay th trc tip cc thit

b s v hot ng trong mi trng. Trong k thut sn xut v truyn dn c xuhng s tin ti thay th han tan qu trnh ghi, s l v lm vic trong mi trng

s. cc thit b s c th ha nhp vo mi trng tng t th cc tn hiu tng

t cn phi c chuyn i sang s v ngc li, tn hiu s thc s tr nn hp dnkhi tn hiu tng t qua b bin i A/D to thnh tn hiu s v c sai s khngng k.1. M ho knh truyn.

c s dng trong cc h s v truyn dn nhm lm cho cc c tnh ca

d liu sau m ho ngun ph hp vi cc c tnh ca my ghi hay knh truyn, mknh truyn s sa i d liu gc nhm t c mt bit cao


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nht c th c trong gii hn c tnh ca di thng knh truyn.dng inmt chiu hay cc tn s thp s c chuyn i trong qu trnh ny trong truyn

dn, d liu truyn dn ph thuc vo tc chuyn i thng tin phi nh hn dunglng knh truyn, dn n s khng thch ng vi knh truyn,di thng knh truyn phi c ci thin khi d liu truyn dn t c c c

tnh tt nht do gii thch cho qu trnh m ho knh truyn. M ho knh truynl lm cho hnh dng ph tn hiu audio s b mo nh nht.Hai t chc AES v EBU c a ra cc tiu chun truyn dn tn hiu

audio s nh tiu chun AES3-1992, ANSIS4-1992, IEC-1958.

2. c im ca tn hiu s liu AES/EBU.

c trng dao din ca nh dng chuyn dng AES/EBUnh dng :S truyn dn ni tip ca hai khung s liu c ly mu v mho tuyn tnh.

Cc thng s pht:- Tn hiu cn bng.

- Cc b ni XLR ( cm) vi chn c v chnci.

Chn 1 :u cp, tn hiu mt(t).

Chn 2 chn tn hiu (khng phn bit) Chn 3 chn tn hiu (khng phn bit) Trkhng ngun: 110 20%.Cn bng


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3. Cc c im dao din knh chun AES/EBU.

nh dng knh ngi ta s dng c dng trong thit b CDS v RDATS (CD-

Compact RISK v RDAT-Rotari Drgital-audio tabe-bng audio s quay ) vi tn hiu

s vo u ra. N cng c bit n trong dao din s

nh dng:

- Truyn dn ni tip ca hai knh s liu pc ly mu v m ho tuyn tnh.

Cc thng s pht.

- Tn hiu ra khng cn bng

- Cc b ni (rc cm m thanh RCA)- Bin i tn hiu ra:500mv ng vi ti 75v

Thng s thu :

- Tn hiu vo khng cn bng

- Cc b ni rc cm m thanh

- Tr khng vo 75

4. Gii m v cc knh tn hiu AES/EBU.

B gii m BPM c dng khi phc chui tn hiu audio s AES/EBU m ho BPM thnh dng s liu. Sau , cc tn hiu s liu hai knh ca b ghp

dng s liu c tch ra thnh hai bit s liu audio song song. Cc bit ph (V, U,

C, P) cng c trch t mi khung con iu chnh qu trnh s l v ng b cc

khung ph v tan b khung

B xen s liu, khi c s hin din ca tp m, c gii thiu nh mt b bin

ng ti bn thu. B bin ng c hiu l c c tnh d thay i trong thi gian

truyn dn ca b gii m bt. B lc c s dng loi tr tp m trc khi xen

s liu.


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H33. B gii m v tch knh dng bt s liu audio AES/EBU ni tip

5. ng b audio s.

Cc tn hiu audio s c to t cc mu ri rc.Nu ta mun chn, trn hay ghpcc tn hiu audio s t cc ngun khc nhau, i hi phi c tn hiu ng b ca

mi mu t ngun chun.Tn hiu audio cn phi c b xung nhm to ra mt tn hiu audio s y ,

trong khng cn cc s c nh ting lch cch hay n trong tn hiu. S phc

tp ca ng b ho c th thay i tu theo vn quan tm l ng b gia ccngun tn hiu audio hay gia cc ngun tn hiu audio v Video.6. ng b gia cc tn hiu audio s .

Tiu chun AESII-1991 ch r kh nng ng b ho c tn s v pha ca cc thitb vn hnh trong audio. Cc my pht chuyn dng phn phi cc tn hiu chun rt

n nh v phc v cho vic ng b ho tn s to iu kin cho chng trnh audioln. Trong trng hp ny thit b sn xut cc thit b con, cn cc my pht chunl my ch. Trong cc audio nh, c th dng tn hiu ra ca b thit b khc thngqua b khuch i phn phi tn hiu s. Tiu chun AESII chr cc mu tn hiu audio s phi cng pha vi tn hiu chun, lch pha cho

php ca khung audio ti u pht l 5% v ti u thu 25%.


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Hai tn hiu ca dio s c tn s ly mu khc nhau hoc khng th ng bcng nhau th cc b chuyn i tc ly mu v ng b c s dng. Qu

trnh ng b thc hin c khi tc ca hai dng s liu c kim sot v cmi quan h vi nhau phc tp v chi ph ca thit b cao hn khi qu trnh ng

b khng c thc hin. V cc mu tn hiu u pht v u thu khng c milin h no.7. ng b gia tn hiu audio s v tn hiu video.

Trong truyn hnh tn hiu m thanh s chun cn phi c ng b vi tn hiuvideo chun nhm ngn chn hin tng tr gia tn hiu audio v tn hiu video, vcho php chuyn mch gia tn hiu audio v tn hiu video khng c ting lch tch.

Trong h thng 625/50, s lng cc mu audio trn mt khung video c quynh chnh xc (1920 mu audio vi tn s l mu 48KHz). Mi quan h vpha gia tn hiu audio v tn hiu video c duy tr mt cch r dng. Tn hiu mthanh tiu chun audio AES 3 c th gi ng b vi tn hiu video bi v tn hiuchun 48 KHz nhn c t tn hiu video chun trong h thng 625 dng.

7.1 Ghi audio s.

nh dng bng audio s DAT (digital audio tape) u tin c pht truyn cho myghi m dn dng (u t quay nn cn g l R-DAT, Rotary digital audio tape). Tuynhin DAT c cht lng cao, nn c dng cho mc ch chuyn dng.Cc tn hiu vo tng t c s ho, m ho knh (iu ch 8-10) trc khi

ghi m trn bng kim loi 3,81mm. nh dng R-DAT gm 4 mode ghi/pht, ly mu48KHz, v 2 mode pht li tc ly mu 44,1KHz.

- Cc c trng ca R-DAT

c trng chung:

- S knh audio:2

- Thi gian ghi:2h (4h, 32KHz, mode2).- u t khng tip t, u ghi trng vi u pht.

- Thi gian d mnh :200 ln so vi bnh thng- Kch thc Casselte:73x54x10,5mm.

c trng in:

- p ng tn s:phng 10Hz22KHz (fS=48KHz)- Di ng:96dB

- Tn s ly mu

- 32KHz


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- 44,12Khz

- 48KHz (cht lng cao) Ly mu:- 16 bit tuyn tnh, 48v44,1Khz

- 12 bit phi tuyn,32 KHz(mode)- Mo:


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thy (tt nht l2:1)v ph thuc vo phc tp ca tn hiu audio gc.

Nh m ho d bo min thi gian m ta c th nn khng tn hao.

- Thut ton vsai: Tn hiu audio c cha cc m lp li cng nh s lng ln

d tha v cc m thanh khng thch hp. D liu lp li c loi b trong qu

trnh m ho v c khi phc li ti phn gii m. K thut DPCM (iu xung m

visai) cng c s dng trong tn hiu audio. Tn hiu audio c tch ra thnh mt

s cc bng tn con c cha mt s m ri rc. Sau m ho bng DPCM v b d

bo thch hp cho cc tn hiu c chu k ngn. Loi m ho thch nghi ny thc hin

trn c s quan st nng lng tn hiu u vo nhm sa cha kch c bc lng t

ph hp. Bc ny c gi l thch

nghi DPCM(ADPCM).- B m ho entropy tch d tha bng cch biu din cc h s lng t ho

ca bng tn con nhm nng cao hiu qu m ho. Cc h s ny c truyn theo

bc tng tn s, to cc gi tr ln ti cc tn s thp v bc chy di ca cc gi tr

nh hoc gn bng 0 cho cc tn s cao.

- Cc thng s qu ti khi d liu: Cc gi tr nh phn t qu trnh bin i(s

sang tng t)Adc, c nhm thnh cc khi d liu c trong min thi gian ln

trong min tn s.

7.3.2. Nn tn hiu s c tn hao.Nn c tn hao nh kt hp hai hay nhiu k thut s l s dng c im cc

HAS l tch cc thnh phn ph c bin nh gia cc thnh phn ph c bin

ln. Phng php

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