JVET-Q0243 Additional support of dependent quantization with 8 states [H. Schwarz, S. Schmidt, P. Haase, T. Nguyen, D. Marpe, T. Wiegand (Fraunhofer HHI)]
This contribution proposes to support dependent quantization with 8 quantization states in addition to the current variant of dependent quantization with 4 quantization states. It is asserted that the implementation complexity for the decoder is virtually not increased. Reportedly, both variants of dependent quantization (4 and 8 states) can be implemented using a single unified decoding process; only the state transition table used depends on the variant chosen. Alternatively, both variants of dependent quantization could be implemented using a single state transition table of 12 states, in which case only the initial state for a transform block depends on the variant of dependent quantization selected.
The following average results are reported for dependent quantization with 8 states relative to VTM-7 (dependent quantization with 4 states) under common test conditions:
AI: –0.43%, 0.07%, 0.14% (Y, Cb, Cr) at 111% encoding time and 99% decoding time;
RA: –0.34%, 0.05%, 0.25% (Y, Cb, Cr) at 106% encoding time and 98% decoding time;
LB: –0.40%, 0.21%, 0.13% (Y, Cb, Cr) at 104% encoding time and 100% decoding time;
LP: –0.37%, 0.16%, –0.02% (Y, Cb, Cr) at 106% encoding time and 95% decoding time.
For the low QP test conditions (QPs 2, 7, 12, 17), the following results are reported:
AI: –0.38%, –0.34%, –0.35% (Y, Cb, Cr) at 120% encoding time and 97% decoding time;
RA: –0.72%, –0.96%, –1.30% (Y, Cb, Cr) at 115% encoding time and 97% decoding time;
LB: –0.78%, –0.30%, –0.22% (Y, Cb, Cr) at 115% encoding time and 95% decoding time;
LP: –0.70%, –0.23%, –0.18% (Y, Cb, Cr) at 117% encoding time and 96% decoding time.
The gain is 0.3-0.4%, but the encoder runtime also increases by 10% and more. It is obvious that the trellis search is duplicating in complexity. This is clearly a worse performance/complexity tradeoff compared to the 4-state version of DQ.
The changes in specification are not large, when some state numbering is modified.
Several experts expressed concern that the complexity/performance tradeoff is not attractive enough.
No action.