Predictive Grayscale Image Coding Scheme Using VQ and BTC

Author: Yu-Chen HuSource: Fundamenta Informaticae 78 (2007) 239–255

Speaker: Meng-Jing TsaiDate: 2011.12.29

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Outline• Introduction• The proposed scheme– Block prediction technique– Vector quantization (VQ)– Block truncation coding (BTC)

• Conclusion

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Introduction• A predictive image compression scheme that

combines the advantages of vector quantization and moment preserving block truncation coding to provide good image quality at a low bit rate.

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• VQ is widely used because it has a simple decoding structure and requires a low bit rate. However, a lot of computational costs are needed in the codebook design procedure and the image coding procedure.

• BTC has the advantages of requiring very low computational cost and providing good

• reconstructed image quality. However, a high bitrate is needed in BTC.

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• To reduce the bit rate

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Vector quantization (VQ)image vector :x=(x1,x2,…,xk)

…

…

Codebook

Original image

d(x,y1)

d(x,y2)

d(x,yN)

NiiyY 1

),...,,( 111 11 kyyy

),...,,( 222 11 kyyy

),...,,(11 kNNN yyy

),(min,...,2,1

min iNi

yxdd

index of ymin

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VQ encoding procedure• Find Closest codeword

Codebook012

255254253

IndexImage vector(21,44,45,78) 2

(24,45,47,76)

(33,32,97,98)(78,22,77,20)

(20,55,53,26)

(20,25,17,11)(12,14,13,16)

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VQ encoding procedure

ImageIndex table

w

Index table

h

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VQ decoding procedure

ImageIndex table

wh

Index table

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Block truncation coding (BTC)• 區塊臨界值 =區塊平均值

11

qqmxb

qmqxa

mx

m

iix

個數大於等於臨界值的像素 : q

sizeblock :m

11

≤

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Block prediction technique

13

≤

14

≤≤

15

BTC

251 7 5 43 169 12 0 16 255 247 200 37 47 56 114 121

98.75

block 44 aConsider

th

x

xx

x

204 17 17 17 204 17 17 17

204 204 204 17 17 17 204 204

: isblock tedReconstruc

1 0 0 01 0 0 01 1 1 00 0 1 1

: is map-Bit

2042.204177.16

795.92

baq

16

≤

17

18

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• Experimental results of image quality of related BTC scheme and VQ with different codebook sizes

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• Results of block prediction technique for BTC and VQ with different search range sr

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Conclusion• This scheme exploits the block similarities

among neighboring image blocks to improve the bit rate of traditional hybrid methods based on VQ and BTC.

• By choosing adequate controlling thresholds, the proposed scheme provides good image quality at a low bit rate.