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Fast Mode Decision And Motion Estimation For JVT/H.264

Fast Mode Decision And Motion Estimation For JVT/H.264. Pen Yin, Hye – Yeon Cheong Tourapis, Alexis Michael Tourapis and Jill Boyce IEEE ICIP 2003 Sep. Outline. Introduction Fast Mode Decision Fast Motion Estimation Simulation Result Conclusion. Introduction(1/4). High coding efficiency

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Fast Mode Decision And Motion Estimation For JVT/H.264

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  1. Fast Mode Decision And Motion Estimation For JVT/H.264 Pen Yin, Hye – Yeon Cheong Tourapis, Alexis Michael Tourapis and Jill Boyce IEEE ICIP 2003 Sep.

  2. Outline • Introduction • Fast Mode Decision • Fast Motion Estimation • Simulation Result • Conclusion

  3. Introduction(1/4) • High coding efficiency • Minor increase in decoder complexity • High encoder complexity • Motion estimation (ME) and mode decision contribute most of the complexity, • In H.264 ME is separately considered from mode decision. • ME is first checked all block types of inter modes, then the mode decisionis made bycomparing the cost of each inter mode

  4. Introduction (2/4) • Minimal the cost defined as follow (ME) • The mode decision is made by minimizing

  5. C B A 2 3 1 D E F 4 5 b c a 6 7 8 d e f g h I H G Introduction (3/4) Assume E is best integer pel Then 1、2 ～ 7 are searched Assume 7 is best integer pel Then a、b ～ h are searched  total : 16 subpel positions are check

  6. Introduction (4/4) • This paper proposed a algorithms to alleviate the encoding complexity by jointly optimize mode decision and ME, while maintaining coding efficiency

  7. Fast Mode Decision(1/4) • Reduce the number of potential modes, eliminate ME for some block types • Decreasesthe number of tested intra modes • Modes are divided into two categories: • inter modes : Skip mode 16x16、16x8 … 4x4 • intra modes : intra 16x16、intra 4x4

  8. Fast Mode Decision(2/4) • Two concepts : • High priority of SKIP mode • Error surface : built by initial 3 mode 16x16 8x8 4x4 • error surface monotonic: or • case 1 : the best two modes are 16x16 and 8x8 only 16x8 and 8x16 • case 2 : the best two modes are 4x4 and 8x8 only 4x8 and 8x4 • Case 3 : error surface is not monotonic all modes

  9. Fast Mode Decision(3/4) • Step1：check SKIP mode • if Jmode(SKIP) < T1, select SKIP as best mode, stop; otherwise go to step2 • step2：check 16x16 and 8x8 • if Jmode(SKIP) <Jmode(16x16) && Jmode(SKIP) < Jmode(8x8), go to step7; otherwise, go to step3 • step3：check 4x4 • if MinJmode= Jmode(8x8) || MaxJmode = Jmode(8x8), go to step4 • if MaxJmode= Jmode(4x4), go to step5 • if MaxJmode= Jmode(16x16), go to step6 • step4：check 16x8, 8x16, 8x4, 4x8; go to step7 • step5：check 16x8, 8x16; go to step7 • step6：check sub-macroblock partition; go to step7 • step7：select the best inter mode • if the energy of the residue for best inter mode is > T2, check intra modes; go to step8 • step8：choose the best mode among all tested modes

  10. Fast Mode Decision(4/4) • In step1,T1= Nbitsλmode( Nbits equals the minimum number of bits required for non SKIP inter modes ) • In step2 comparing SKIP with 16x16 and 8x8 • assume that the RD cost for SKIP is the minimal, so no other modes need to be checked • In step3, check the monotonic • In step7, assume that inter modes have higher priority than intra modes ( T2 = 0 )

  11. Fast Motion Estimation(1/6) • ME process involves two steps： • Fast integer pel motion search： • Based on predictive motion estimation algorithm : Enhanced Predictive Zonal Search (EPZS) • Fast subpel motion refinement： • This paper mainly discuss the subpel ME • Propose two patterns of fast subpel ME and early stop criterion

  12. Fast Motion Estimation • EPZS : • ME around initial predictors • Refinement around the best predictor using diamond or square patterns • refinement is performed around the second best predictor or the median predictor • Avoid being trapped into local minimum

  13. C B A 2 3 1 D E F 4 5 b c a 6 7 8 d e f g h H I G Fast Motion Estimation • First pattern : • Assume that the diamond positions are more important than corner positions • TOTAL 12 point need to check

  14. C B A 2 3 1 D E F 4 5 b c a 6 7 8 d e f g h H I G Fast Motion Estimation • Second pattern: • store the position for the best integer and its best diamond position • 3 half point need to check

  15. C B A 2 3 1 D E F 4 5 b c a 6 7 8 d e f g h H I G Fast Motion Estimation • Second pattern : • For quarter pel search, the best position and second best position in half pel search are chosen.

  16. Fast Motion Estimation • Three cases : • Case 1 : two best pels are integer-pel two quarter pels on the same row/column will be tested • Case 2 : two best pels are at the same row/column, 3 quarter pels between these two pels will be tested. • Case 3 : two best pels are in a diagonal position (ex: E、8)  3 quarter-pel (two diamond positions and one corner position) will be tested

  17. Fast Motion Estimation • Step1 : after integer search, examine the current minimum SAD, if SAD < T1, stop; otherwise, go to step2; • Step2 : half pel positions, examine the current minimum SAD, if SAD <T2, stop; otherwise, go to step3; • Step3 : examine the quarter pel positions.

  18. Simulation Result • 85% to 90% complexity reduction can be achieved versus the reference software, while coding efficiency is only slightly decreased. • average PSNR gain (∆PSNR) • bitrate reduction (bitrate)

  19. Conclusion • In this paper presents a new algorithm to jointly optimize motion estimation and mode decision. • Simulation results demonstrate that our scheme can maintain coding efficiency at considerably lower complexity.

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