An Efficient Low Bit-Rate Video-coding Algorithm Focusing on Moving Regions

1. 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

2. 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.

3. Low Bit-Rate Video Coding Using Patterns The eight patterns for moving region approximation

4. 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.

5. 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.

6. 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.

7. The rule for classifying the types of MB

8. AMB RMB

9. 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.

10. 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

11. Encoder

12. Decoder

13. 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

14. An example of pattern approximation for the sequence “News” Detected moving regions Results of pattern approximation

15. The principle of interframe coding for RMB

16. 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.

17. Rearrangement of the residual errors

18. Simulation Results

19. PSNR for the first 100 frames for the video sequence “Akiyo”

20. Encoding time saved per frame compared to H.263

21. Simulation results “Akiyo” with different bit-rates

22. 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.