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An Efficient Low Bit-Rate Video-coding Algorithm Focusing on Moving Regions. Kwok-Wai Wong, Kin-Man Lam, Wan-Chi Siu IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, OCTOBER 2001. Introduction.
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An Efficient Low Bit-Rate Video-coding Algorithm Focusing on Moving Regions Kwok-Wai Wong, Kin-Man Lam, Wan-Chi Siu IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, OCTOBER 2001
Introduction • Conventional block-based coding schemes do not take into account the arbitrary shape of moving objects. • Eight patterns are pre-defined to approximate the moving regions in a macroblock. • Experimental results show both the prediction efficiency and the compression efficiency are improved.
Low Bit-Rate Video Coding Using Patterns The eight patterns for moving region approximation
Moving Region Detection T: thresholding function B:structuring element of morphological operations, a square pattern of size 3*3 • If < threshold, the value of M(x,y) is assumed to be zero. • The value of the moving regions is nonzero.
Moving Region Detection • Static MBs (SMBs) • the contents of the MB are all zero or the size of moving region is smaller than a threshold. • Active MBs (AMBs) • The contents of all the sub-blocks have a nonzero value. • Active-region MBs (RMBs) • The remaining MBs. • One of the eight predefined patterns will be used to approximate the moving regions.
Moving Region Detection Mk : the Kth MB in the processed frame M(x,y) PN(i,j) : the pre-defined pattern number N If the computed minimum Dk,N is greater than a threshold,the MB is assumed to be an AMB.
AMB RMB
Architecture of the Encoder and Decoder • Type of MB • SMB: encoded as a skipped MB • AMB: the conventional block-based encoding method is used • RMB: “Pattern Matching” unit • Pattern Matching • To find a pre-defined pattern which is the best representation of the moving region in a RMB. • Uses 3 bits to represent PMB(pre-defined pattern information), and then encoded by VLC.
Architecture of the Encoder and Decoder • Block Rearrangement • If RMB, “Block Rearrangement” unit rearrange the residual errors of the moving regions into a block of size 8*8 • “Inverse Rearrangement” unit • Motion Estimation • AMB: “Block Predictor” • RMB: “Moving region predictor” • Uses 1 bit to represent MPMODE(motion predictor mode), together with the motion vector are encoded by VLC
Motion Estimation and Compensation • The contents of SMB are copied from the reference frame directly. • The matching process is more precise as the static region is neglected in motion estimation. • Conventional method: 256 “minus” ,255 “sum”, 256 “absolute” operations • New: 64 “minus”, 63 “sum”, 64 “absolute” operations
An example of pattern approximation for the sequence “News” Detected moving regions Results of pattern approximation
Prediction Error Encoding • AMB: conventional DCT-based coding method • The prediction errors of the moving region in a RMB are rearranged to a block of size 8*8, and DCT transform is then employed. • Only a block is needed to encode for a RMB,and the compression ratio is increased.
PSNR for the first 100 frames for the video sequence “Akiyo”
Conclusion • Eight pre-defined patterns were chosen by experiments to represent moving regions. • This approach outperforms the H.263 in terms of the PSNR and the rum-time for sequences of smooth motion.