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Predictive Grayscale Image Coding Scheme Using VQ and BTC. Author: Yu-Chen Hu Source: Fundamenta Informaticae 78 (2007) 239–255 Speaker: Meng -Jing Tsai Date: 2011.12.29. Outline. Introduction The proposed scheme Block prediction technique Vector quantization (VQ)
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Predictive Grayscale Image Coding Scheme Using VQ and BTC Author: Yu-Chen Hu Source: FundamentaInformaticae 78 (2007) 239–255 Speaker: Meng-Jing Tsai Date: 2011.12.29
Outline • Introduction • The proposed scheme • Block prediction technique • Vector quantization (VQ) • Block truncation coding (BTC) • Conclusion
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.
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.
Vector quantization (VQ) image vector : x=(x1,x2,…,xk) d(x,y1) d(x,y2) … … d(x,yN) Codebook Original image index of ymin
0 1 2 Image vector (21,44,45,78) 253 254 255 VQ encoding procedure • Find Closest codeword Codebook (12,14,13,16) (20,25,17,11) Index (24,45,47,76) 2 (78,22,77,20) (33,32,97,98) (20,55,53,26)
VQ encoding procedure w h Image Index table Index table
VQ decoding procedure w h Image Index table Index table
Block truncation coding (BTC) • 區塊臨界值=區塊平均值
≤ ≤
Experimental results of image quality of related BTC scheme and VQ with different codebook sizes
Results of block prediction technique for BTC and VQ with different search range sr
Conclusion • This scheme exploitsthe block similarities among neighboring image blocks to improve the bit rate of traditional hybrid methods based on VQ and BTC. • By choosing adequate controllingthresholds, the proposed scheme provides good image quality at a low bitrate.