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16th Meeting: Geneva, October 2019 2019-10-04 14:07
Non-CE6: Disabling MTS for 64xN and Nx64 CUs
Authors: J. Jung WILUS Dong-Ha Kim WILUS G. Ko WILUS J. Son WILUS J. Kwak WILUS Jason Jung
Abstract
In this contribution, the block size condition for applying MTS (Multiple Transform Selection) is proposed when the maximum transform size is equal to 32. In VVC Draft 6, the maximum transform size is signalled in the SPS (Sequence Parameter Set) and it can be configured to either 32 or 64. When the maximum transform size is equal to 32, 64xN and Nx64 (N>=4) CUs are partitioned into 32xMin(32, N) and Min(32, N)x32 TUs, respectively. For the partitioned TUs, MTS is allowed and MTS index (tu_mts_index) is coded. However, when the maximum transform size is equal to 64, MTS is not allowed to 64xN and Nx64 (N>=4) CUs. This contribution proposes to disallow MTS for 64xN and Nx64 (N>=4) CUs when the maximum transform size is equal to 32. In the proposed method, only DCT-II and transform skip mode are allowed and MTS index is not coded for 64xN and Nx64 (N>=4) CUs. This would harmonize the maximum CU block size that can utilize MTS as 32x32 irrespective of the signaled maximum transform size. It is reportedly shown that the proposed method achieves -0.02% (AI), -0.02% (RA) and -0.05% (LDB) BD-rates with same encoding and decoding times when the maximum transform size is configured to 32 in VTM-6.0. Additionally, when inter MTS is enabled (--MTS=3), the proposed method achieves 0.03% (RA) and -0.09% (LDB) BD-rates with 93% and 92% encoding times.
Meeting Notes
JVET-P0540 Non-CE6: Disabling MTS for 64xN and Nx64 CUs [J. Jung, D. Kim, G. Ko, J. Son, J. Kwak (WILUS)]

In this contribution, the block size condition for applying MTS (Multiple Transform Selection) is proposed when the maximum transform size is equal to 32. In VVC Draft 6, the maximum transform size is signalled in the SPS (Sequence Parameter Set) and it can be configured to either 32 or 64. When the maximum transform size is equal to 32, 64xN and Nx64 (N>=4) CUs are partitioned into 32xMin(32, N) and Min(32, N)x32 TUs, respectively. For the partitioned TUs, MTS is allowed and MTS index (tu_mts_index) is coded. However, when the maximum transform size is equal to 64, MTS is not allowed to 64xN and Nx64 (N>=4) CUs. This contribution proposes to disallow MTS for 64xN and Nx64 (N>=4) CUs when the maximum transform size is equal to 32. In the proposed method, only DCT-II and transform skip mode are allowed and MTS index is not coded for 64xN and Nx64 (N>=4) CUs. This would harmonize the maximum CU block size that can utilize MTS as 32x32 irrespective of the signaled maximum transform size. It is reportedly shown that the proposed method achieves -0.02% (AI), -0.02% (RA) and -0.05% (LDB) BD-rates with same encoding and decoding times when the maximum transform size is configured to 32 in VTM-6.0. Additionally, when inter MTS is enabled (--MTS=3), the proposed method achieves 0.03% (RA) and -0.09% (LDB) BD-rates with 93% and 92% encoding times.

This has small benefit under non-CTC, and the encoder runtime reduction could also be achieved in a non-normative way by signalling MTS off in the 64xN and Nx64 TU with very small overhead.

References:
JVET-N1010 JVET-O2001
Cited:
JVET-P0026 JVET-P0680 X
ARCHIVE v2 :
._JVET-P0540-v2.docx ._JVET-P0540.pdf ._JVET-P0540_Table1_MTS1.xlsm ._JVET-P0540_Table2_MTS3.xlsm JVET-P0540-v2.docx JVET-P0540.pdf JVET-P0540_Table1_MTS1.xlsm JVET-P0540_Table2_MTS3.xlsm
Decisions
This has small benefit under non-CTC, and the encoder runtime reduction could also be achieved in a non-normative way by signalling MTS off in the 64xN and Nx64 TU with very small overhead.
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