JVET-AJ0090 AHG12: temporal ALF [L. Xu, Y. Yu, H. Yu, D. Wang (OPPO)]

This contribution proposes an adaptive loop filter that uses temporal reconstructed information as the input to a filter whose output will enhance the current picture. The proposed temporal adaptive loop filter (TALF) is implemented on top of ECM-14.0 reference software. The simulation results show that the proposed method can achieve the following BD-rates gain over the anchor:

RA: -0.13%/0.26%/0.25%, 100.6%/102.6%EncT/DecT

LDB: -0.16%/0.54%/0.21%, 102.2%/104.2%EncT/DecT

The input samples to TALF are retrieved from the reference pictures as identified by the motion vectors. Motion is clipped to integer precision to fetch corresponding samples.

Another mode of filtering uses collocated samples from the closest reference picture in the reference picture list.

The proposed TALF is applied to inter coded blocks (using samples from refernce pictures) and IBC blocks (using samples from current picture before ALF).

No fixed filters. Up to 8 history TALF sets can be stored for use by future pictures.

Currently, the TALF coefficients are signalled in the slice header, instead of using APS. It was commented that using an APS like other ALF filters is more desirable.

It was commented that this proposal would introduce some latency, the gain may not sufficient to justify the latency.

Multiple experts expressed interest in the proposal.

It was agreed to investigate this in an EE. The proposal needs to be modified to carry the coefficients in an APS.