Chuong 4_Nen Anh

8/14/2019 Chuong 4_Nen Anh

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Xl nh s

M ha v nnnh s


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32 Ni dungTrong phn ny chng ta stm hiu vcc

kthutc p dng nn nh:Mcch ca nnnh

Cc kiu dtha dliu

Cc bc trong m hnh nn v gii nnCc thut ton m ha v gii m


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Mcch ca nnnh

nh skhngc nn scn mt lng ln khngg an u r v ng ng ruy n

V d nh mu kch thc 640 x 480 cn khng.

Mc ch ca vic nn nh l gim slng dliu cnbiu dinnh. Do sgim khng giancnlu trv tngc tc ng truyn


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Cc cch tip cn

Phng php nn bo ton thng tin

Thng tin c bo ton Tlnn thp

Phng php nn lm mt thng tin Thn tin khn c bo ton

Tlnn cao


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Dliu vs. thng tin

Dliu (data)l phng tin c dng

truy n t ithng tin

Nn d liu l phng php gim sl n d li u cn biu din 1 l nthng tin cho trc vi tiu ch gi li c cn nhiu thn tin cn tt


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Tlnn

compression

Tlnn:


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Dtha dliu

a u ng :

V d :


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Cc kiu dtha dliu

(1) Dtha m ha

(2) Dtha khng gian & thi gian


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M hnh thng tin

Qu trnh thng tinc to ra c coi l mt qu

Mt s kin ngu nhin E vi xc sut P(E) s cl n tin co bn :

Entropy ca ngun tin: l lng tin trung bnh trn 1 ktca ngun tin (source symbol). Gisngun tin c

1, 2,, J


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Lng tin trn mi pixel

Githit cc gi trmc xmc to ra bi mt bin, k

bng:

Lng tin trung bnh:

n vthng tin

units/pixelEntro


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Dtha m ha

Code: danh sch cc k hiu (symbol) dngxy, , ,

Code word: Mt chui cc k hiuc sdngbiu din 1 thn tin ho c s ki n v d : thn tin vmc xm).

Code word length: Scc k hiu trong mi tm


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Dtha m ha (Cont)

V d: cho bcnh c cc thng snhsaun c c x

rk: mc xm thk-thp(rk): Xc sut xut hin mc xm rk

k k

Chiu di trung bnh ca cc tm:

Sbit cnm ha bcnh:


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Dtha m ha (Cont)

Trng hp l(rk) = constant


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Dtha m ha

Trng hp l(rk) = variable length

dtha m ha:

Tlnn:


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Dtha m ha

dtha m ha:

Trong:


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Dtha khng gian

a s ng n su xu n c ckhi pixel:

image

Tnh lng tin trung bnh


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M hnh m hanh

Mapper:Bininhu vo theo cch c thlmgim dtha thng tin gia cc pixel


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M hnh m hanh

Quantizer: Lng t ha l bc tng hoc gimcc gi tr u ra ca bc mapper theo cc mc

mong mun


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M hnh m hanh

Symbol encoder:M ha k tl bc gn m cdi ngn nht cho k tc tn sut xy ra nhiu

.


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M hnh gii mnh

,

c thc hin theo thtngc li.

Ring bc gii lng tkhng thkhi

lng t


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Tiu chnh gi cht lng

Trong qu trnh nnnh, ngoi vic quan tm ti tl nn cht l n nh sau khi ii nn cn hic xem xt.

nh gi cht lng nh u ra bng cch so

Tiu chnh gi: Ch uan:da vo kin n i uan st Khch quan:da vo cng cton hctnh


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nh gi chquan


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nh gi khch quan

Mean-square signal-to-noise ratio(SNR)


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Nn khng mt dliu


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Huffman coding

Backward Pass

n c c u v c o c c n n

theo chiu ngc li


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Huffman coding

avg us ng u man co ng:

Lavg assuming binary codes:


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Huffman decoding

m


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V d

Cho cc k hiu c xc sut nhsau:

K hiu Xc sut

B 0,4

C 0 1

D 0,02

E 0,08

Lp bng m Huffman cho cc k hiu trnF 0,2

Thc hin gii m trong trng hp nhnc dy k hiu: 00110001010101000110


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cim ca m Huffman

hin ch1 ln

M Huffman c gi lm khi

v mi ku c u n ng m m c n .

Vic gii m tng k hiu c thc hintc thi v khng phthuc k hiu trc vsau


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M ha shc

Chui cc k hiu ngunc m hacng nhau

Khng c stngng 1 -1 gia k hiu

n un v t m

nhng tlnn cao hn


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M ha shc

Chui k tngun c gn 1 tm shc tng ng vi 1 kho ng con trongon [0,1]

Khi sl n k t tron bn tin tn lnkhong con biu din chui sthub l i

m tchui cng nhiu


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M ha shc

1 2 3 3 4

,

2) Subdivide [0, 1) based on the probability of i

3) Update interval by processing source symbols


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V d

Encode

a1a2a3a3a4

[0.06752, 0.0688)

,

0.068


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32Gii m

.

0.8

.

0.72

.

0.688

.

0.5856

.

0.57152

a4

Decode 0.572

a3

0.4 0.56 0.624 0.5728 056896

a2

0.2 0.48 0.592 0.5664

0.56768a1

..0.56 0.56 0.5664


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32M LZW Lempel-Ziv-Welch

Thut ton m ha:

Re eat:

Tm dy k tdi nht wc trong t in

Cp nht dy k twa vo trong t in,

trong wal dy k tkhng c trongt in


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1. BA is not in the Dictionary; insertBA, output the code for its prefix:code(B)2. AB is not in the Dictionary; insertAB, output the code for its prefix:code(A)

. .

BAA is not in Dictionary; insertBAA, output the code for its prefix:code(BA)

4. AB is in the Dictionary.

ABA is not in the Dictionary; insertABA, output the code for its prefix:code(AB). s no n e c onary; nser , ou pu e co e or s pre x:co e

6. AA is in the Dictionary and it is the last pattern; output its code:code(AA)

The compressed message is:


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V d2: M ha dy k tsau:

1. BA is not in the Dictionary; insert BA, output the code for its prefix: code(B)

2. AB is not in the Dictionary; insert AB, output the code for its prefix: code(A)

3. BA is in the Dictionary.

s no n c onary; nser , ou pu e co e or s pre x: co e

4. AB is in the Dictionary.

ABRis not in the Dictionary; insert ABR, output the code for its prefix: code(AB)

5. RRis not in the Dictionary; insert RR, output the code for its prefix: code(R). .

RRA is not in the Dictionary and it is the last pattern; insert RRA, output code for its prefix:

code(RR), then output code for last character: code(A)

The compressed message is:

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Example: Chui cha nn: aaabbbbbbaabaaba

S ng ts = T ng s t 8

= 16 * 8

= s

Tm s lng bit sau khi nn:

S lng bits = Tng s t m* 12

= 7 * 12

= 84 bits

Note: Mi nhca t in c kch thc 12 bit

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Use LZW to decompress the output sequence

1. 66 is in Dictionary; output string(66) i.e. B2. 65 is in Dictionary; output string(65) i.e. A, insert BA

3. 256 is in Dictionary; output string(256) i.e. BA, insert AB

. . . ,

5. 65 is in Dictionary; output string(65) i.e. A, insert ABA

6. 260 is not in Dictionary; outputprevious output + previous output first character: AA, insert AA


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32M hnh m hanh

Mapper:Bininhu vo theo cch c thlmgim dtha thng tin gia cc pixel

u am o: p: www. a er ar.org scre e-

Cosine-Transform-Tutorial.htm

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32Bini cosine ri rc (DCT)

DCT biu din tn hiu (tp cc s) di dngng c c m cos v c c n s c n au.

V dtn hiu:

Cc hsca php bini DCTc tnh bic ng c:

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Vi k = 0: ta c hsw0c gi l hs1 chi u (DC coefficient):

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Vi k khc 0: cc hswkc gi l hs xoay chi u (AC coefficient):

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Bini DCT 2 chiu:

forward

inverse

if u=0 if v=0

if u>0 v

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Bi i i i (DCT)


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Bini DCT vi n = 8:

D = TT x A x T A l ma tr n cn bini

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Bi i i i (DCT)


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Mi quan hgia hm cos vnh

Hs1 chiu Chiu tng ca tn s

xoaytng

tn s

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Bi i i i (DCT)


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V d:

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Bi i i i (DCT)


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M h h h h


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32M hnh m hanh

Quantizer: Lng t ha l bc tng hoc gimcc gi tr u ra ca bc mapper theo cc mc

mong mun

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f Lng t ha


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32Lng tha

Quantization

Q(u,v): quantization table

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f Chun nn JPEG


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32Chun nn JPEG

Cu trc ca chun nn JPEG

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of Zig zag scan


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32Zig-zag scan

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Chuong 4_Nen Anh