Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 1 Chng 1 GII
THIU MATLAB 1.1Tng quan v Matlab 1.1.1 Khi nim v Matlab
Matlablmtngnnglptrnhthchnhbccaocsdng gii cc bi ton v k thut. Matlab
tch hp c vic tnh ton, th hin kt qu, cho php lp trnh, giao din lm
vic rt d dng cho ngi s dng. D
liucngvithvinclptrnhsnchophpngisdngcthc c nhng ng dng sau y.-S dng
cc hm c sn trong th vin, cc php tnh ton hc thng thng. -Cho php lp
trnh to ra nhng ng dng mi.-Cho php m phng cc m hnh thc t.-Phn
tch,kho st v hin th d liu.-Vi phn mm ho cc mnh.
-Chophpphttrin,giaotipvimtsphnmmkhcnhC++,Fortran.1.1.2 Tng quan v
cu trc d liu ca Matlab, cc ng dng
Matlablmththngtnggiao,ccphntdliulmtmng (mng ny khng i hi v kch
thc). Chng cho php gii quyt cc vn
linquannlptrnhbngmytnh,cbitsdngccphptnhvma
trnhayvectorvcthsdngngnngChocFortranlptrnhrithc hin ng dng lp trnh
bng cc cu lnh gi t Matlab. Matlab c vit tt t ch MATrix LABoratory
tc l th vin v ma trn, t phn mm Matlab c vit nhm cung cp cho vic
truy cp vo phn mm ma trn mt cchddng,phnmmmatrnnycphttrinbicccngtrnh
Linpack v Eispack. Ngy nay Matlab c pht trin biLapack v Artpack to
nn mt ngh thut phn mm cho ma trn.a. D liu
DliucaMATLABthhindidngmatrn(hocmngtng Nn nh S S Dng Matlap Svth:
Hong Cao phi-081481D 2 qut), v c cc kiu d liu c lit k sau y: -Kiu n
single, kiu ny c li v b nh d liu v n i hi t byte
nhhn,kiudliunykhngcsdngtrongccphptnh ton hc, chnh xc km
hn.-Kiudoublekiunylkiuthngdngnhtcaccbintrong Matlab. -Kiu
Sparse.-Kiu uint8,uint16. . . -Kiu char v d Hello-Kiu cell.-Kiu
Structure.TrongMATLABkiudliudoublelkiumcnhsdngtrongcc php tnh s
hc.b. ng dngMATLABto iu kin thun li cho:-Cc kho hc v ton hc.-Cc k
s, cc nh nghin cu khoa hc. -Dng MATLAB tnh ton, nghin cu to ra cc
sn phm tt nht trong sn xut.c. Toolbox l mt cng c quan trng trong
Matlab Cng c nycMATLAB cung cp chophp bn ng dng cc k thut phn
tch,thit k, m phng cc m hnh.Ta c th tm thy toolbox trong m trng lm
vic ca.-Mng nron.-Logic m. -Simulink. 1.1.3 H thng MATLAB H thng
giao din ca MATLAB c chia thnh 5 phn: Mi trng pht trin. y l ni t cc
thanh cng c, cc phng tin gip chng ta s dng cc Nn nh S S Dng Matlap
Svth: Hong Cao phi-081481D 3 lnh v cc file,ta c th lit k mt s nh
sau.+ Desktop. + Command Window. + Command History. + Browsers for
viewinghelp.Th vin, cc hm ton hc bao gm cc cu trc nh tnh tng, sin
cosin, atan,atan2etc...,ccphptnhnginnccphptnhphctpnhtnh ma trn
nghch o, tr ring, chuyn i fourier, laplace, symbolic library.Ngn ng
MATLAB. l cc ngn ng cao v ma trn v mng, vi cc dng lnh, cc hm, cu
trc d liu vo, c th lp trnh hng i tng. ha trong MATLAB. Bao gm cc cu
lnh th hin ho trong mi trng 2D v 3D, to cc hnh nh chuyn ng, cung cp
cc giao din tng tc gia ngi s dng v my
tnh.Giaotipviccngnngkhc.MATLABchophptngtcvicc ngn ng khc nh C,
Fortran 1.1.4Lm quen vi matlab nh a s desktop (ca s ln nht), v cc
ca s ph ca n. Trc tin khi ng MATLAB bn click vo biu tng MATLAB.exe,
trnmnhnhxuthincassau.(Xemhnhv1.1)Caschacc Nn nh S S Dng Matlap
Svth: Hong Cao phi-081481D 4
thanhcngc(Giaodinngivmy)cnthitchovicqunlccfiles, cc bin, ca s lnh,
c th coi desktop l cc panel gm cc , vng,qun l v tc dng ca tng ca s
nh c qun l bi desktop. 1.1.5 Cc ca s Lm vic ca MATLAB a. Ca s
Command windowLcasgiaotipchnhcaMatlabbiylninhpgitrcc bin, hin thgi
tr, tnh ton gi tr ca biu thc,thc thi cc hm c sn
trongthvin(dnglnh),hoccchm(dngfunction)dongidnglp trnh ra trong
M_files.Cclnhcnhpsaudunhc>>,vnucsaisttrongqu trnh g (nhp) lnh
th hy nhn phm Enter cho n khi nhn c du nhc >>. Thc thi lnh
bng nhn phm Enter.G cc lnh sau:>> A= pi/2 ;>> B= sin(A)
B=1 Hoc chng trnh son tho trong M-file di y: % Chuong trinh trong
M-file x= 0:pi/6:2*pi;y=sin(x);plot(x, y);% chuong trinh clu vi tn
file l ve_sin.m Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 5
b. Ca s command History CcdngmbnnhpvotrongcasCommandwindow(ccdng ny
c th l dng nhp bin, hoc c th l dng lnh thc hin hm no )
cgilitrongcasCommandHistory,vcasnychophptas dng li nhng lnh bng
cchclick chut ln cc lnh hoc cc bin, nu nh bn mun s dng li bin .
click ichut lnlnh hocbin sdng li c. Ca s Workspace L ca s th hin tn
cc bin bn s dngcng vi kch thc vng
nh(sbytes),kiudliu(lp),ccbincgiiphngsaumilntt chng trnh. Click
ichut lnbin xem dliu(hocthay igi tr)
Ngoiranchophpthayigitri,cngnhkchthccabin bng cch click i chut ln cc
bin. Hoc click vo nt bn tri ngay cnh nt save V d khi chn bin (gi th
l bin b) ri click (hoc click chut vo nt cnh nt save) ta c ca s sau
gi l Array Editor. Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D
6
Tiu l tn bin b, nh dng d liu c tn l: Numeric format, mc nh l dng
short, Kch thc size l 1 by 3 (tc l mt hng v 3 ct) ta
cththayikchthcnybngcchthayisctrongkchthc size.Dng ca s ny lu cc bin
di l d liu ca bin b, ta c th
thayichngbngcchthayigitrtrongccTtcccbinu c lu trong Workspace trong
th hin c kch thc (Size), s Bytes v kiu d liu (class) (8 bytes cho
mi phn t d liu kiu double c th l 24 bytes dnh cho b v 8 bytes dnh
cho a). d. Ca sM-fileLmtcasdngsonthochngtrnhngdng,thcthi chng trnh
vit trong M-file bng cch g tn ca file cha chng trnh trong ca s
Commandwindow.KhimtchngtrnhvittrongM-file,thtutheongdngcth,tu theo
ngi lp trnh m chng trnh c th vit di dng sau:-Dng Script file: Tc l
chng trnh gm tp hp cc cu lnh vit di dng lit k, khng c bin d liu vo
v bin ly gi tr ra. Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D
7 - Dng hm function: c bin d liu vo v bin ra. 1.2 Cc hm chuyn i kiu
nhVi cc thao tc nht nh, s tht hu ch khi c th chuyn i nh t dng ny
sang dng khc. Chng hn, nu ta mun lc mt nh mu c lu tr di dng nh s, u
tin ta nn chuyn i n thnh dng nh RGB. Khi
tapdngphplctinhRGB,Matlabslcgitrcngtngng
trongnh.NutalcnhsMatlabnginchptphplctimatrn nh s v kt qu s khng c
ngha. Ch :Khi chuyn i mt nh t dng ny sang dng khc, nh kt qu c th
khc nh ban u. Chng hn, nu ta chuyn i mt nh mu ch s sang mt nh cng ,
kt qu ta s thu c mt nh en trng. Danh sch sau y s lit k cc hm c s
dng trong vicchuyn i nh: + dither: To mt nh nh phn t mt nh cng en
trng bng cch trn, to mt nh ch s t mt nh RGB bng cch trng (dither).
+ gray2id: To mt nh ch s t mt nh cng en trng . + grayslice: To mt
nh ch s t mt nh cng en trng bng cch t ngng.
+im2bw:Tomtnhnhphntmtnhcng,nhchshaynh RGB trn c s ca ngng nh sng.
Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 8 + ind2gray: To mt
nh cng en trng t mt nh ch s. + ind2rgb: To mt nh RGB t mt nh ch
s.+mat2gray:Tomtnhcngentrngtdliutrongmtmatrn bng cch ly t l gi liu.
+ rgb2gray:To mt nh cng en trng t mt nh RGB. + rgb2ind: To mt nh ch
s t mt nh RGB. Ta cng c th thc hin cc php chuyn i kiu ch s dng c
php caMatlab.Chnghn,tacthconvertmtnhcngsangnhRGB bng cchghp ni 3
phn copy ca ma trn nh gc gia 3 chiu: RGB=cat(3,I,I,I ); nh RGB thu
c c cc ma trn ng nht cho cc mt phng R,G,B v vy nh hin th ging nh
bng xm. 1.3 Giao din ho GUI 1.3.1 Khi nim tin cho vic s dng cc ng
dng hay chng trnh m ta vit
chngtacthtoragiaodinhaGUI(GraphicUserInterface)gia ngi dng v
matlab. Trong giao din ny ta c th xut d liu di hai dng vn bn v ha.
Mi mt GUI c th c mt hay nhiu giao din. Vic to GUI to nn mt cng c
nhp xut d liu mt cch trc quan, nhanh chng v rt thun tin. Ngoi ra c
th dng GUI gim st cc qu trnh, hin th cc i tng 1.3.2 Cch to GUIC hai
cch to ra GUI: To GUI bng cch vit lnh trc tip trong M-file v to GUI
bng cng c ha. 1.3.2.1 To GUI bng lnh to giao din GUI nh hnh bn di
ta lm cc bc sau: Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 9
B1:TokhunggiaodinvttnchoGUIvitnWelcometoGUIvi nhng dng lnh sau:
namefig= 'Welcome to GUI';figpos = get(0,'DefaultFigurePosition');
% lay vi tri mac nhienfigpos(1)= figpos(1)-10;figpos(2)=
figpos(2)-10; figpos(3)= figpos(3)+10;figpos(4)= figpos(4)+10;% Tao
figurefig=figure( ...'Name', namefig, ...'NumberTitle','off',
...'Position',figpos); Ta thu c hnh bn: Hnh 1.2 Giao din GUI Nn nh
S S Dng Matlap Svth: Hong Cao phi-081481D 10 B2: To khung ha truy
xut nh v dng ch Interface Matlab axs=axes('Position',[0.05 0.4 0.65
0.55]); % text txtpos=[10 50 425
50];txt=uicontrol(...'Style','text',...'BackgroundColor',[0.8 0.8
0.8],...'ForegroundColor',[0 0 1],...'String','Interface Matlab
',... 'Position',txtpos,...'Fontname','Times New Roman',...
'FontWeight','Bold',...'FontSize',34); Nn nh S S Dng Matlap Svth:
Hong Cao phi-081481D 11
B3:ToccntnhnctnSphere,Picture,Closevvitlnhcho chng. %Close button
closeHndl=uicontrol(... 'Style','pushbutton', ...
'Units','normalized', ... 'Position',[p1+0.01 p4-0.35 p3-0.025
0.05], ... 'String','Close', ... 'Foregroundcolor','b',...
'Fontsize',9,... 'Callback','close');%Sphere buttonsph=uicontrol(
... 'Style','pushbutton', ... 'Units','normalized', ...
'Position',[p1+0.01 p4-0.1 p3-0.025 0.05], ... Nn nh S S Dng Matlap
Svth: Hong Cao phi-081481D 12 'String','Sphere', ...
'Foregroundcolor','b',... 'Fontsize',9,...
'Callback',['[x,y,z]=sphere(35);', 'surfl(x,y,z);', 'axis
equal']);%Picture button pic=uicontrol(...'Style','pushbutton',
...'Units','normalized', ...'Position',[p1+0.01 p4-0.225 p3-0.025
0.05], ...'String','Picture',
...'Foregroundcolor','b',...'Fontsize',9,...'Callback','imshow(uigetfile(''*.bmp;*.BMP;*.tif;*.TIF;*.jpg''))');Kt
qu ta thu c: nh 3 Kt qu thu c bng lnh Nn nh S S Dng Matlap Svth:
Hong Cao phi-081481D 13 1.3.2.2 To GUI bng cng c ha Trn y ta xem xt
cch to GUI bng phng php th cng. Ta c th to GUI bng cng c ho. Bng
hai cch nh sau:. Hnh 1.4: To giao din GUICch 1: G lnh guide trong
ca s command Window Cch 2: Click chut vo biu tngguide( )trn thanh
cng c. Khi g lnh guide ta thy xut hin mt hp th thoi nh hnh sau:
Create New GUI: to giao din GUI mi. Nn nh S S Dng Matlap Svth: Hong
Cao phi-081481D 14 Open Existing GUI: m nhng giao din c trc.
ChngtachnCreateNewGUIsauchnBlankGUI(Default) to GUI trng v thit lp
cc thng s theo yu cu. Kt qu cho ra mt layout rng nh hnh bn: Sau khi
m hp thoai to GUI ta lm cc bc sau: B1: thit k giao din GUI nh bi
trn c hnh sau: Son tho thuc tnh Chy th Son Menu Cc phn t thit k Vng
thit k Vit lnh Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 15
nh 5 a s thit k giao din GUI B2: Vit lnh cho cc nt nhn (button).
Function sph_Callback(hObject, eventdata, handles)
[x,y,z]=sphere(35); surfl(x,y,z); axis equal Function
pic_Callback(hObject, eventdata, handles)
imshow(uigetfile({'*.tif;*.bmp;*.gif;*.jpg'},'pick an image file'))
Function clo_Callback(hObject, eventdata, handles) Close Kt qu thu
c: nh 6 Kt qu thu c bng cng c ha Nn nh S S Dng Matlap Svth: Hong
Cao phi-081481D 16 Chng 2 NN NH S 2.1 Cc khi nim v nh 2.1.1 im nh
(Picture Element) Gc ca nh (nh t nhin) l nh lin tc v khng gian v
sng. x l bng my tnh (s), nh cn phi c s ho. S ho nh l s bin i
gnngmtnhlintcthnhmttpimphhpvinhthtvvtr
(khnggian)vsng(mcxm).Khongcchgiaccimnhc thit lp sao cho mt ngi khng
phn bit c ranh gii gia chng. Mimtim nh vygi lim nh (PEL:
PictureElement) haygi tt l Pixel. Trong khun kh nh hai chiu, mi
pixel ng vi cp ta (x, y). Hnh 2.1 Hnh minh ha ca pixel nh ngha: im
nh (Pixel) l mt phn t ca nh s ti to (x, y) vi xm
hocmunhtnh.Kchthcvkhongcchgiaccimnhc chn thch hp sao cho mt ngi cm
nhn s lin tc v khng gian v mc xm (hoc mu) ca nh s gn nh nh tht. Mi
phn t trong ma trn c gi l mt phn t nh. 2.1.2 Mc xm ca nh
Mtimnh(pixel)chaictrngcbnlvtr(x,y)caim nh v xm ca n. Di y chng ta
xem xt mt s khi nim v thut ng thng dng trong x l nh.
a)nhngha:Mcxmcaimnhlcngsngcanc 1 pixel Nn nh S S Dng Matlap Svth:
Hong Cao phi-081481D 17 gn bng gi tr s ti im . Hnh 2.2 Hnh biu din
mc xm ca nh s b) Cc thang gi tr mc xm thng thng: 16, 32, 64, 128,
256 (Mc 256 l mc ph dng. L do: t k thut my tnh dng 1 byte (8 bit)
biu dinmc xm:Mc xmdng 1 byte biu din: 28=256mc, tc l t 0 n 255).c)
nh en trng:nh en trng ch bao gm 2 mu: mu en v mu trng (khng cha mu
khc) vi mc xm cc im nh c th khc nhau. Ngi ta phn mc en trng thnh L
mc Nu s dng s bit B=8 bit m ha mc en trng (hay mc xm) th L c xc nh
:L=2B (trong v d ca ta L=28= 256 mc) Nu L bng 2, B=1, ngha l ch c 2
mc: mc 0 v mc 1, cn gi l nh nh phn. Mc 1 ng vi mu sng, cn mc 0 ng
vi mu ti. Nu L ln hn 2 ta c nh a cp xm. Ni cch khc, vi nh nh phn mi
im nh c m ha trn 1 bit, cn vi nh 256 mc, mi im nh c m ha trn 8 bit.
Nh vy, vi nh en trng: nu dng 8 bit (1 byte) biu dinmc xm, s ccmc xm
c th biu din c l 256. Mimcxmc biu din di dng l mt s nguyn nm trong
khong t 0 n 255, vi mc 0biudinchomccngennhtv255biudinchomccng sng
nht.nh nh phn kh n gin, cc phn t nh c th coi nh cc phn t logic. ng
dng chnh ca n c dng theo tnh logic phn bit i tng Nn nh S S Dng
Matlap Svth: Hong Cao phi-081481D 18 nh vi nn hay phn bit im bin vi
im khc. d)nhmu:trongkhunkhlthuytbamu(Red,Blue,Green)
tonnthgiimu)trongR,G,Blmtgitrxmvcbiubiu din bng 1 byte, khi cc gi
tr mu: 28*3=224 16,7 triu mu. Mimu cng phn thnh L cpmu khc nhau
(thng L=256).Mi khong ny biu din cho cng sng ca mt trong cc mu
chnh. Do , lutrnhmungitacthlutrtngmuringbit,mimulu
trnhmtnhacpxm.Do,khnggiannhdnhchomtnhmu ln gp 3 ln mt nh a cp xm
cng kch c. P(x, y) = (R, G, B) - H mu CMY: l phn b ca h muRGB (C,
M, Y)=(1, 1, 1)-(R, G, B) HayC+R=M+G=Y+B=1 => H mu ny thng c dng
trong my in.- H mu CMYK: trong K l m nht ca mu K= min (C, M, Y)
P(x, y) = (C-K,M-K,V-K,K).+ V d: Vi(C1, M1, Y1)ta s c K=min (C1,
M1, Y1) vy CMYK = (C1-K, M1-K, Y1-K, K) Hnh 2.3 H ta RGB 2.1.3 nh
ngha nh s Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 19
nhsltphpccimnhvimcxmphhpdngmt nh gn vi nh tht.
Mtnhsgiscbiudinbnghmf(x,y).Tpconccim nh l S; cp im nh c quan h vi
nhau k hiu l p, q. 2.2 Mt s khi nim nn nh s 2.2.1.Nn d liu (Data
Compression) Nndliulqutrnhlmgimlngthngtin"dtha"trongd liu gc v do
vy, lng thng tin thu c sau nn thng nh hn d liu gc rt nhiu. Vi d liu
nh, kt qu thng l 10 : 1. Mt s phng php
cnchoktqucaohn.Theoktqunghincuccngbgnyti vin k thut Georgie,k thut
nn fractal cho t s nn l 30 trn 1.Ngoi thut ng "nn d liu, do bn cht
ca k thut nyn cn c mt s tn gi khc nh: gim d tha,m ho nh gc.T hn hai
thp k nay, c rt nhiu k thut nn c cng b trn cc ti liu v nn v cc phn
mmnn d liu xut hin ngy cng nhiu
trnthngtrng.Tuynhin,chacphngphpnnnoccoil
phngphpvnnng(Universel)vnphthucvonhiuyutvbn cht ca d liu gc. Trong
chng ny, chng ta khng th hy vng xem xt tt c cc phng php nn. Hn na,
cc k thut nn d liu chung c
trnhbytrongnhiutiliuchuynngnh.y,chngtachcpcc phng php nn c c th
ring cho d liu nh.2.2.2.T l nn (Compression rate)
Tlnnlmttrongccctrngquantrngnhtcamiphng php nn. Tuy nhin, v cch nh
gi v cc kt qu cng b trong cc ti liu
cngcncquantmxemxt.Nhnchung,ngitanhnghatlnn nh sau: T l nn = 1rx %
Vir: l t s nn c nh ngha: r = kch thc d liu gc/ kch thc d liu thu c
sau nn. Nh vy hiu sut ca nn l: (1-t l nn) x %. Khi ni n kt qu nn,
chng ta dng t s nn, th d nh 10 trn 1 Nn nh S S Dng Matlap Svth:
Hong Cao phi-081481D 20 c ngha l d liu gc l 10 phn sau khi nn ch c
1 phn.Tuy nhin, cng phithy rng nhng s o ca mtphng php nn ch c gi tr
vi chnh s nn , v rng hiu qu ca nn cn ph thuc vo kiu d liu nh nn. T
l nn cng ch l mt trong cc c trng c bn ca phng php nn. Nhiu khi t l
nn cao cng cha th ni rng phng php
lhiuquhnccphngphpkhc,vcnccchiphkhcnhthi
gian,khnggianvthmchcphctptnhtonna.Thdnhnn
phcvtrongtruyndliu:vntralhiuqunnctnghpvi ng truyn
khng.Cngcnphnbitnndliuvinnbngtruyn.Mcchchnh
cannlgimlngthngtindthavdntigimkchthcdliu. Tuy vy,i khi qu trnh nn
cng lm gim bng truyn tn hiu s ho thp hn so vi truyn tn hiu tng
t.2.2.3. Cc loi d tha d liu Nh trn ni, nn nhm mc ch gim kch thc d
liu bng cch loi b d tha d liu. Vic xc nh bn cht cc kiu d tha d liu
rt c ch cho vic xy dng cc phng php nn d liu khc nhau. Ni mt cch
khc, cc phng php nn d liu khc nhau l do s dng cc kiu d tha d liu
khc nhau. Nn c4kiu d tha chnh: a. S phn b k t
Trongmtdykt,cmtsktctnsutxuthinnhiuhn mt s dy khc. Do vy, ta c th m
ho d liu mt cch c ng hn. Cc dyktctnsutcaocthaybimttmnhphnvisbtnh;
ngc li cc dy c tn sut thp s c m ho bi t m c nhiu bt hn. y chnh l bn
cht ca phng php m ho Huffman. b. S lp li ca cc k t Trong mt s tnh
hung nh trong nh, 1 k hiu (bit "0" hay bit "1") c lp i lp li nhiu
ln. K thut nn dng trong trnghp ny l thay
dylpbidymigm2thnhphn:slnlpvkhiudngm.
PhngphpmhokiunyctnlmholotdiRLC(RunLength Coding). Nn nh S S Dng
Matlap Svth: Hong Cao phi-081481D 21 c. Nhng mu s dng tn sut C th c
dy k hiu no xut hin vi tn sut tng i cao. Do vy,c th m ho bi t bit
hn. y l c s ca phng php m ho kiu t in do Lempel-Ziv a ra v c ci tin
vo nm 1977, 1978 v do c tn gi l phng php nn LZ77, LZ78.Nm 1984,
TerryWelch ci tin hiu qu hn v t tn l LZW (Lempel-Ziv- Welch). d. d
tha v tr Do s ph thuc ln nhau ca d liu, i khi bit c k hiu (gi tr)
xut hin ti mt v tr, ng thi cth on trc s xut hin ca cc gi tr cc v tr
khc nhau mt cch ph hp. Chng hn, nh biu din trong mt
lihaichiu,mtsimhngdctrongmtkhidlulixuthin trong cng v tr cc hng khc
nhau. Do vy, thay vlu tr d liu, ta ch cn lu tr v tr hng v ct. Phng
php nn da trn s d tha ny gi l phng php m ho d on.Cch nh gi d tha nh
trn hon ton mang tnh trc quan nhm biu thmt ci gxut hin nhiu ln. i
vi d liunh, ngoi c th chung ,n cn c nhng c th ring. Th d nh c ng
dng khng cn ton b d liu th ca nhm ch cncc thng tin c trng biu dinnh
nhbinnhhayvngngnht.Dovy,cnhngphngphpnnring cho nh da vo bin i nh
hay da vo biu din nh.2.2.4. Phn loi cc phng php nn C nhiu cch phn
loi cc phng php nn khc nhau.-Cchphnloithnht:davonguynlnn.Cchnyphncc
phng php nn thnh2 h ln: Nnchnhxchaynnkhngmtthngtin:Hnybaogmcc phng
php nn m sau khi gii nn ta thu c chnh xc d liu gc. Nn c mt mt thng
tin: H ny bao gm cc phng php m sau khi gii nn ta khng thu c d liu
nh bn gc. Trong nn nh,ngi ta gi l cc phng php" tm l th gic". Cc
phng php ny li dng tnh cht ca mt ngi, chp nhn mt s vn xon trong
nhkhikhi phc li. Ttnhin,ccphngphpnychchiuqukhimvnxonlchp Nn nh S S
Dng Matlap Svth: Hong Cao phi-081481D 22 nhn c bng mt thng hay vi
dung sai no .-Cchphnloithhai:davocchthcthchinnn.Theocch ny,ngi ta
cng phn thnh hai h: Phngphpkhnggian(SpatialDataCompression):Ccphng
php thuc h ny thc hin nn bng cch tc ng trc tip ln vic ly mu ca nh
trong min khng gian. Phng php s dng bin i (Transform Coding): Gm cc
phng php tc ng ln s bin i ca nh gc m khng tc ng trc
tip.-Cchphnloithba:davotritlcasmho.Cchnycng phn cc phng php nn thnh
2 h: Cc phng php nn th h th nht: Gm cc phng php m mc tnh ton l n
gin, th d nh vic ly mu, gn t m,... Cc phng php nn th h th hai: Da
vo mc bo ho ca t l nn. Trong cc phn trnh by di y,ta s theo cch phn
loi ny. Cng cn phi k thm mt cch phn loi th t do Anil. K. Jain nu
ra. Theo cch ca Jain,cc phng php nn gm 4 h chnh: Phng php im. Phng
php d on. Phng php da vo bin i. Cc phng php t hp (Hybrid).Thc ra
cch phn loi ny l chia nh ca cch phn loi th ba v da vo c ch thc hin
nn. Xt mt cch k lng n cng tng ng cch phn loi th
ba.Nhnchung,qutrnhnnvgiinndliucthmtmtcchtmtt theo s di y. Qu trnh
nnD liu gcD liu nn Qu trnh gii nn nh 24S chc nng qu trnh nn d liu
Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 23
2.3 Bin i cosine ri rc (DCT- Discrete cosine Transform) 2.3.1
Phng php bin i Binicosinerirc(DCT)biudinnhdidngtngcacc cosine ca cc
thnh phn bin v tn s khc nhau ca nh. Hm dct2 tnh DCT hai chiu camt
nh. DCT c tnh cht mvi cc nh in hnh, hu ht cc thng tin v nh ch tp
trung trong mt vi h s ca DCT, trong khi cc h s cn li ch cha rt t
thng tin. V l do ny, DCT thng c s dng trong cc ng dng nn nh khc
nhau nh hiu sut gn nh ti u ca niviccnhctngquancaogiaccimnhlncn.Chng
hn, DCT l trung tm ca gii thut nn nh theo chun quc t thng c
bitvitnJPEG(tnnydonhmphttrintra:JointPhotographic Experts Group)DCT
hai chiu ca ma trn A c kch thc MxN c nh ngha nh sau : 1 10 0(2 1)
(2 1)cos cos2 2M Npq p q mnm nm p n qB AM Nt to o = =+ +=vi 0 10 1p
Mq Ns s s s Trong : 1/(2/ )pMMo=
00 1pp M=s s v 1/(2/ )qNNo=
00 1qq N=s s Cc gi trBpq c gi l cc h s ca bin iDCT. DCT c th
bini ngc c v bin i ngc ca n cho bi cng thc : 1 10 0(2 1) (2 1)cos
cos2 2M Nmn p q pqp qm p n qA BM Nt to o = =+ +=vi 0 10 1m Mn Ns s
s s Trong : 1/(2/ )pMMo=
00 1pp M=s s v 1/(2/ )qNNo=
00 1qq N=s s BiuthcDCTngccthcxemxtkhicoirngmimatrnAkch thc MxN
nh l tng ca MN hm c dng : (2 1) (2 1)cos cos2 2p q pqm p n qBM Nt
to o+ + Nhng hm ny c gi l nhng hm c s ca DCT. H s DCT Bpq
cthcxemnhtrngschomihmcs.Viccmatrn8x8,64 Nn nh S S Dng Matlap Svth:
Hong Cao phi-081481D 24 hm c s c minh ho bi nh sau: nh 25 nh minh
ha ma trn 8x8 2.3.2 Nn tn hao da vo DCT
Giithutnnctnhaocbitnnhiunhtcllgiithut dng DCT. y l gii thut c chun
ha vi tn gi JPEG (ly t tn gi ca t chc nh ra tiu chun nn ny: Joint
Photographic Experts Groups
(Nhmlienktccchuyngiaxlnh).ChunJPEGcsdngm ho nh a mc xm, nh mu. N
khng cho kt qu n nh lm vi nh en trng. ChunJPEG cung cp gii thut cho
c hai loi nn lnnkhngmtmt thng tin v nn mt mt thng tin. S khi ca gii
thut nn v gii nn nh JPEG: NH GC Phn kh i 8x8 8x8 8x8 Lng t ho Bng
lng t ...... M ho Bng m NH NN DCT Nn nh S S Dng Matlap Svth: Hong
Cao phi-081481D 25 Hnh 2.6S khi ca gii thut nn v gii nn nh JPEG nn
nh theo gii thut JPEG, ta chia nh thnh cc khi 8x8 (hoc 16x16). Mi
khi 8x8 ny s c x l ring bit qua cc bc ca qu trnh
nnnh.utin,tathchinbiniDCTthunivimikhi.Nh
chngtabit,doccinnhkcnnhauthngctnhtngquanrt cao, php bin i DCT thun
c xu hng tp trung huht nnglng ca bc nh vo trong mt vi h s DCT tn s
thp. y l c s ta thc hin nn nh. Vi mt khi nh kch thc 8x8 trch t nh
ngun, hu ht cc h s ca n u bng 0 hoc gn bng 0. Nh vy, ta c th khng
cn biu din cchsnykhitruyndliunhi.LurngbnthnbiniDCT khng lm mt mt
thong tin ca nh gc, n ch chuyn cc thng tin ny v mt dng khc m ta c
th m ha mt cch hiu qu hn. Sau khi qua b bin i DCT, mi h s trong s
64 h s bin i DCT c lng t ha da vomt bng gi tr lng t c thit kk lng.
Mtphngphplngtngincthdnglchgilimtvihs DCT tn s thp (cc h s c gi tr
ln) cn tt c cc h s cn li gn bng 0. trong chun nn JPEG, mi h s DCT s
c chia cho mt trng s v tr tng ng trong mt ma trn lng t 8x8, sau lm
trn v s nguyn gn nht. Sau khi lng t ha, cc h s bin i DCT s c sp xp
theo mt chui zig-zag bt u t thnh phn DC, ri n thnh phn AC Cui cng
cc h s ny c chuyn thnh chui bit nh phn bng k thut m haa ra nh nn.
Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 26
cngongiim,bgiimsthhinqutrnhngcli:Gii m entropy, sau nhn cc h s thu
c vi phn t tng ng ca ma trn lng t, ri bin ingc DCT ti to li nh ban
u.a.Phn khi Chun nn JPEGphn nh ra cc khi 8x8. Cng on bin i nhanh
Cosinhaichiuchocckhi8x8trahiuquhn.BiniCosinchocc khi c cng kch c c
th gim c mt phn cc tnh ton chung nh vic tnh h s Cji. Khi n=8 chng
ta ch cn tnh h s Cji cho 3 tng (8= 23), s cc h s l: 4 + 2 + 1 = 7.
Nu vi mt nh 1024x1024, php bin i nhanh Cosin mt chiu theo hng ngang
hoc hng dc taphi qua 10 tng (1024 = 210). S cc h s Cji l: 512 + 256
+ 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 1021. Thi gian tnh cc h s
Cji vi ton b nh 1024x1024 ln gp 150 ln so vi thi gian tnh ton cc h
s ny cho cc khi. Bin i Cosin i vi cc khi c kch thc nh s lm tng chnh
xc khi tnh ton vi s du phy tnh, gim thiu sai s do lm trn sinh ra.
Do cc im nh k cn c tng quan cao hn, do php bin i Cosin cho tng khi
nh s tp trung nng lng hn vo mt s t cc h s bin i. Vic loi bt mt s h
s nng lng thp trong cc khi ch to ra mt mt thng tin cc b gip nng cao
cht lng nh. nh s c chia lm B khi vi:
BNBMlNkMB = =|.|
\||.|
\|' ' Cc khi c xc nh bi b s (m,n) vi m = [0..MB-1] v
n=[0..NB-1],ymchthtcakhitheochiurng,nchthtcakhitheo chiu di. Phn
khi thc cht l xc nh tng quan gia to ring trong khi vi to thc ca im
nh trong nh ban u. Nu nh ban u k hiu Image[i,j] th ma trn biu din
khi (m,n) l x[u,v]c tnh: | | v nl u mk age v u x + + = , Im ] , [
Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 27 16) 1 2 (16) 1 2
() ,7070(4) , (2 2 1 12 1122 12 1H + H +===k nCosk nCos k nkkk X n
n xc cb.Bin i Bin i l mt cng on ln trong cc phng php nn s dng php
bin i. Nhim v ca cng on bin i l tp trung nng lng vo mt s t cc h s
bin i. Cng thc bin i cho mi khi l: Trong ) 8 0 (0021111< <
==kkkhikhikc ) 8 0 (0021222< < ==kkkhikhikc
ThuttonbininhanhCosinhaichiuchomikhitrongtrng hp ny s bao gm 16 php
bin i nhanh Cosin mt chiu. u tin, ngi
tabininhanhCosinmtchiuchoccdyimnhtrnmihng.Ln
ltthchincho8hng.SauembininhanhCosinmtchiutheo tng ct ca ma trn va
thu c sau 8 php bin i trn. Cng ln lt thc hin cho 8 ct. Ma trn cui
cng s l ma trn h s bin i ca khi tng
ng.TrongsgiinntaphidngphpbiniCosinngc.Cng thc bin i ngc cho khi
8x8: ) 8 0 (0021111< < ==kkkhikhikc Trong ) 8 0 (0021222<
< ==kkkhikhikcc.Lng t ha Khilngthotrongsnnngvaitrquantrngvquyt
16) 1 2 (16) 1 2 () ,7070(4) , (2 2 1 12 11 22 12 1H + H +===k
nCosk nCos n nn nx k k Xk k c c Nn nh S S Dng Matlap Svth: Hong Cao
phi-081481D 28 nh t l nn ca chun nn JPEG. u voca khi lng t ho l cc
ma trn h s bin i Cosin ca cc khi im nh. gim s b lng t, ngi ta tm
cchquy cc h s cc khi vcngmt khong phn b. Chunnn JPEG ch s dng mt b
lng t ho. Gisrngcchsuchmtnhxcsutxuthinnhnhau.Chngtas cn chnh li h s
yjbng php gn: jj jjyyo = Vij l trung bnh cng ca h s th j. oj l lch
c bn ca h s th j. d.Nn uvocakhinngmhaithnhphn:thnhphncchsmt chiu v
thnh phn cc h s xoay chiu. Thnh phn cc h s mt chiu Ci(0,0)vi i =
0,1,..., 63 cha phn lnnnglngtnhiuhnhnh.Ngitakhngnntrctipccgitr
Ci(0,0) m xc nh lch ca Ci(0,0): ) 0 , 0 ( ) 0 , 0 (1 i i iC C d =+
dicgitrnhhnnhiusoviCinntrongbiudinduphyngtheo chun IEEE754 thng cha
nhiu chui bit 0 nn c th cho hiu sut nn cao
hn.GitrC0(0,0)vcclchdicghiramttptm.Tpnyc nn bng phng php nn
Huffman.ThnhphncchsxoaychiuCi(m,n)vi1sms7,1sns7 cha cc thng tin chi
tit ca nh. nng cao hiu qu nn cho mi b h s
trongmtkhingitaxplichngtheothtZigZag.Cthhnhdung hnh ZigZagnh bng
trang bn. TcdngcaspxplitheothtZigZagltoranhiuloths ging nhau. Chng
ta bit rng nng lng ca khi h s gim dn t gc trn
bntrixunggcdibnphinnvicspxplicchstheotht
ZigZagstoiukinchocchsxpxnhau(cngmclngt)nm trn mt dng. Nn nh S S Dng
Matlap Svth: Hong Cao phi-081481D 29
MikhiZigZagnycmhotheophngphpRLE.Cuimi khi u ra ca RLE, ta t du kt
thc khi EOB (End Of Block).Sau , cc khi c dn li v m ho mt ln bng
phng php m Huffman.Nhcduktthckhinncthphnbitchaikhicnh nhau khi gii
m Huffman. Hai bng m Huffman cho hai thnh phn h s tt nhin skhc
nhau. c th gii nn c, chng ta phi ghi li thng tin nh: kch thc nh,
kch thc khi, ma trn T, lch tiu chun, cc mc to li, hai bng m
Huffman, kch thc khi nn mt chiu, kch thc khi nn xoay chiu... v ghi
ni tip vo hai file nn ca hai thnh phn h s. Tm li, DCT lm gim tng
quan khng gian ca thng tin trong block (khi). iu cho php biu din
thch hp min DCT do cc h s DCT c xu hng c phn d tha t hn. iu ny c
ngha l DCT gi mt phn ln nng lng tn hiu vo cc thnh phn bini c tn s
tng i thp lu tr hoc truyn dn, to 0 v cc gi tr rt thp i vi thnh phn
tn s cao. Nh c tnh ca h thng nhn ca mt ngi, cc h s DCT c
thcmhaphhp,chcchsDCTquantrngnhtmicm
havtruyni.DCTthunkthpviDCTnghchskhngchotntht 0 23910202135
1481119223436 57121823333748 613172432384749 1416253139465057
1526304045515658 2729414452555962 2842435354606163 Nn nh S S Dng
Matlap Svth: Hong Cao phi-081481D 30 nu di t m ca h s l 13 n 14
bits cho tn hiu video u vo c s
habngccmudi8bit.Nuhsclngthabng11bit(hoc ngn hn), th nn bng DCT s c
tn hao. Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 31 Chng 3
CHNG TRNH NN NH 3.1 Giao din chng trnh nh 3 Giao din chng trnh 3.2
M hnh nn 3.3 Qu trnh nn v gii nn DCT Khi chn nh gc a vo nn DCT, trc
khi nn ta kim tra nh c phi l nh xm khng. Nu khng phi th chuyn n v
dng nh xm sau thc hin cc bc nn nh nh sau: B1: Chuyn d liu nh sang
kiu double. B2: Chia nh gc ra thnh nhiu khi (nh con) kch thc 8x8.
B3:BinithunDCTivimikhinh8x8.Tacthtoma trn bin i DCT A kch thc NxN
bng hm: A=dctmtx(N). V d: A=dctmtx(8) Ma trn bin i DCT A c gi tr:
0.35360.35360.35360.35360.35360.35360.35360.3536
0.49040.41570.27780.0975-0.098-0.278-0.416-0.49
0.46190.1913-0.191-0.462-0.462-0.1910.19130.4619
0.4157-0.098-0.49-0.2780.27780.49040.0975-0.416 Lng t ha nh Gc nh
con 8x8 nh con 8x8 nh con 8x8 nh con 8x8 DCT M ha nh nn Bng lng t
ha Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D 32
0.3536-0.354-0.3540.35360.3536-0.354-0.3540.3536
0.2778-0.490.09750.4157-0.416-0.0980.4904-0.278
0.1913-0.4620.4619-0.191-0.1910.4619-0.4620.1913
0.0975-0.2780.4157-0.490.4904-0.4160.2778-0.098 B4: Lng t ha cc h s
DCT. Thchinlngthabngcchnhncckhinh8x8bini DCT vi bng lng t ha, y n l
mt mt n (mask) ma trn 8x8. Mc
chcabcnylnhmchgilinhngphntmangnnglngca khi nh hay ni chnh xc l 10
phn t u tin ca khi nh 8x8. Mt n (mask) ma trn 8x8 gi li 10 phn t:
11110000 11100000 11000000 10000000 00000000 00000000 00000000
00000000 B5: Gii m cho ra nh (nn + gii nn DCT). V d: Thc hin nn v
gii nn DCT i vi nh Cameraman.tif. B1 Chuyn d liu nh sang kiu
double. I = imread('cameraman.tif'); I = im2double(I);
B2:Chianhgcrathnhnhiukhi:(nhcon)kchthc8x8.Mt khi nh 8x8 c chia c gi
tr pixel: 0.61180.62350.61960.60780.61960.61180.62350.6196
0.62750.60390.61570.61960.61570.62350.61960.6196
0.61180.62350.61960.60780.61960.61180.62350.6196
0.62750.60390.61570.61960.61570.62350.61960.6196
0.61180.60.60780.62350.62350.60780.61180.6078
0.60780.60780.60780.61570.61180.62350.59610.6196 Nn nh S S Dng
Matlap Svth: Hong Cao phi-081481D 33
0.61180.60.61570.61180.60.60780.60390.6078
0.62350.62350.61180.61960.61180.62350.61570.6314 B3: Bin i DCT
4.9211-0.0080.00260.00180.00930.00410.0101-0.002
0.015-0.0030.00210.0028-0.0080.0008-0.0090.0157
0.0080.0020.0132-0.006-0.009-0.006-0.002-0.003
-0.020.0003-0.012-0.0020.0036-0.0040.0021-0.001
0.0132-0.0020.00130.00240.00340.0011-0.0080.0021
-0.0080.00360.0044-0.006-0.010.00020.00150.0056
0.0078-0.0030.004-0.005-0.008-0.021-0.008-0.003
-0.0110.0039-0.005-0.008-0.005-0.002-0.0150.0123 B4: Lng t ha
4.9211-0.0080.00260.00180000 0.015-0.0030.002100000
0.0080.002000000 -0.020000000 00000000 00000000 00000000 00000000
B5: Gii m 0.61580.61510.61460.61480.61580.6170.61790.6183
0.61790.61740.61690.61720.61830.61950.62040.6208
0.61850.61810.61780.61820.61930.62060.62140.6218
0.61510.61480.61460.61520.61630.61750.61820.6184
0.61030.61010.610.61050.61160.61250.6130.6131
0.6090.60880.60870.60920.610.61060.61080.6108
0.61250.61230.61210.61250.61310.61340.61340.6131
0.61670.61650.61630.61660.6170.61720.6170.6166 nh cui cng cho ra cc
thng s gi tr pixel nh bng trn v kt qu thu c hnh nh bn di. Nn nh S S
Dng Matlap Svth: Hong Cao phi-081481D 34 a)b) nh 32 a) nh gc; b) nh
nn 3.4 Cc on m lnh 3.4.1 Chn nh function chonanh_Callback(hObject,
eventdata, handles)
[filename,pathname]=uigetfile({'*.tif;*.bmp;*.gif;*.jpg'},'pick an
image file'); S=imread([pathname,filename]); axes(handles.anh1);
imshow(S); guidata(hObject, handles); 3.4.2 Nn DCT function
nen_Callback(hObject, eventdata, handles) S=handles.S;
axes(handles.anh2); if size(S,3)==3 S=rgb2gray(S); end I =
im2double(S); T = dctmtx(8); B = blkproc(I,[8 8],'P1*x*P2',T,T');
mask = [1 1 1 1 0 0 0 0 Nn nh S S Dng Matlap Svth: Hong Cao
phi-081481D 35 1 1 1 0 0 0 0 0 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]; B2 =
blkproc(B,[8 8],'P1.*x',mask); I2 = blkproc(B2,[8
8],'P1*x*P2',T',T); imshow(I2) handles.I2=I2; guidata(hObject,
handles); 3.4.3 Xem Pixel nh gc function
pixel_goc_Callback(hObject, eventdata, handles) S=handles.S;
axes(handles.anh3); if size(S,3)==3 S=rgb2gray(S); end
I=im2double(S); I1=imresize(I,[8 8]); himage=imshow(I1);
hfigure=figure; hpanel=impixelregionpanel(hfigure,himage); 3.4.4
Xem Pixel nh nn function pixel_nendct_Callback(hObject, eventdata,
handles) S=handles.S; axes(handles.anh4); if size(S,3)==3
S=rgb2gray(S); end Nn nh S S Dng Matlap Svth: Hong Cao phi-081481D
36 I=im2double(S); I1=imresize(I,[8 8]); T=dct2(I1);
himage=imshow(T); hfigure=figure;
hpanel=impixelregionpanel(hfigure,himage); 3.4.5 Xem gi tr tng
Pixel function ketqua_Callback(hObject, eventdata, handles)
S=handles.S; if size(S,3)==3 S=rgb2gray(S); end I=im2double(S);
A=imresize(I,[8 8]); p=get(handles.hang,'string');%gn p gi tr chui
trong handles.hang q=get(handles.cot,'string');%gn q gi tr chui
trong handles.cot p=str2num(p);%chuyn t gi tr chui sang gi tr s
q=str2num(q); p=round(p);%lm trn gi tr s q=round(q); c=0; p1=0;
q1=0; goc=0; if (p>0)&(q>0)if (p
