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Block Truncation Coding Using Pattern Fitting

Source: Pattern Recognition, vol.37, 2004, pp.2131-2139Authors: Bibhas Chandra Dhara, Bhabatosh ChandaSpeaker: Shu-Fen Chiou( 邱淑芬 )Date: 2004/09/08

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Outline Introduction BTC (Block Truncation Coding) Purposed method Experimental results Conclusions Comments

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Introduction Since 1970s the block truncation coding

(BTC) has been studied a lot.•High PSNR but low compression ration.

A modified scheme of BTC is proposed to achieve high compression ration and keeping PSNR as high as possible.

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BTC (1/3)

將影像分成不重疊的n n方塊

計算每個方塊的量化臨界值與重建階

建立位元圖 編碼並送出位元圖

編碼並送出重建階

原影像

解碼位元圖 重建影像方塊 組成重建影像

編碼端

解碼端

建立重建階

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BTC (2/3)14

614

915

215

6

9712

214

414

7

89 9013

514

5

85 92 9912

0

12316/)120152149146( X

1478/)145152149146( b

44 block

998/)1208912297( a

146

149

152

156

97122

144

147

89 90135

145

85 92 99120

146

149

152

156

97122

144

147

89 90135

145

85 92 99120

1 1 1 1

0 0 1 1

0 0 1 1

0 0 0 0

ba , +

147 147 147 147

99 99 147 147

99 99 147 147

99 99 99 99

X

X

Bit pattern

216

1688

bpp

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BTC (3/3)

(a) Original image (b) Reconstructed image with conventional BTC(PSNR=32.89 and bpp=2)

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Purposed method

將影像分成不重疊的n n 方塊

Pattern fitting

Encoding the block

Entropy coding and send

原影像

receive 重建影像方塊 組成重建影像

編碼端

解碼端

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Pattern fitting (1/4)

Set of two-level patterns

Njp j , 2, ,1 ,

Pattern book

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Pattern fitting (2/4)146

149

152

156

97122

144

147

89 90135

145

85 92 99120

1p

2p

0

01 2

0

ji pxj ike xf

1

11 2

1

ji pxj ikke xf

1

0

/1

and /1

where

1

0

ji

ji

pxi

pxi

xfkk

xfk

10 jjj eee

jj em min arg

44 block

408318901 e

1450 1001

1390 1061

8204673532 e

1,emin 21 em j

8 ,16 kk

8 ,16 kk

10

212

2

1

22

11

1

1

1

)(2

2

2

mm

xfk

m

xfk

m

kkk

kd

kkk

kkmA

dAb

dAa

k

ii

k

ii

146

149

152

156

97122

144

147

89 90135

145

85 92 99120

44 block

2p

1m

8 ,16 kk

26)816(82

1626

12381682

)1682(26123

26

15797

123

2

1

d

A

m

m

Pattern fitting (3/4)

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Pattern fitting (4/4)

Output image after pattern fitting

79.31PSNR

375.116

688bpp

664log

64

, 2, ,1 ,

2

N

Njp j

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Encoding the block (1/2)

otherwise,

, if 0

th

th

dd

ddd

88.0bpp

61.31PSNR

4

thd

Considering entropy coding for and 8-bits for Ad

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Encoding the block (2/2)

minmax2

minmax

min

log exceedingnot interger largest theis where

2

AAl

AA

AAA

l

4

1iiic AwAA

0.64bpp 31.57,PSNR

codingentropy with ,

dA

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Reconstruction

,0 if

,0 if 0~

2

~min

minmax

ddd

dd

AAAA

A

th

l

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Experimental results

Original image Reconstructed image

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Experimental results

Original image Reconstructed image

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Experimental results

Conventional BTC (PSNR=32.89 and bpp=2) Purposed method (PSNR=31.59 and bpp=0.64)

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Experimental results

Experimental result of proposed method and others

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Conclusions Instead of determining bit-pattern for a block, an

optimum bit-pattern is selected from a pattern-book.

Our method is presented to achieve higher compression ration and keeping PSNR as high as possible.

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Comments 如何決定 wi? 計算壓縮率時 , 是否也應考慮 Pattern book?