6.3Discussion and Conclusions
The current design for LC used 6-tap DIF, and for HE used 12-tap DCTIF.
It was noted that for the LC configuration, the implementation of the DIF did not take into account some available symmetry in the operation of the filtering process.
For the HE case, several proposals reportedly showed both improved coding efficiency and reduced (or not increased) complexity.
It was remarked that it may be possible to combine some ideas from multiple proposals.
It was remarked that dynamic range (as well as memory bandwidth) may be more of an issue with longer filters.
It was noted that longer filters may increase subjective ringing/mosquito artifacts.
It was remarked that the JCTVC-D344 8x8 separable filter with 6 bit tap values seemed interesting, relative to the current HE case, and it could provide 4.4% improvement relative to DIF for the current LC case. A cross-check had been provided in JCTVC-D059.
It was remarked that using the JCTVC-D344 interpolation while prohibiting the encoder from using 1/4-sample increments simultaneously both vertically and horizontally could provide 2% gain relative to current DIF and complexity reduction relative to the current DIF.
Toshiba and Qualcomm proposals also provide special treatment of certain positions.
A participant remarked that, especially for hardware implementation, having the same consistently-applied filter regardless of positions is desirable.
Decision: Adopted the JCTVC-D344 8x8 separable filter with 6 bit tap values (for both HE and LC, without restrictions on MV values).
Further study was also planned to be conducted (e.g., in a CE).
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