Method and apparatus for signaling adaptive loop filter parameters in video coding
According to a method for Adaptive Loop Filter (ALF) processing of reconstructed video, multiple indicators are signaled in slice at an encoder side or parsed at a decoder side, where the multiple indicators are Adaptive Parameter Set (APS) indices associated with temporal ALF filter sets for the ALF processing. A current indicator is determined from the multiple indicators, where the current indicator is used to select a current ALF filter set. Filtered-reconstructed pixels are derived for the current block by applying the current ALF filter to the current block. In another method, if the ALF processing applied at a target sample requires an outside sample on other side of a target virtual boundary from the target sample, the outside sample is replaced by a padded sample.
1. A method for Adaptive Loop Filter (ALF) processing of reconstructed video, the method comprising:
receiving reconstructed pixels, wherein the reconstructed pixels comprise a current block included in a current Coding Tree Block (CTB) in a slice;
signaling ALF filter sets in respective Adaptive Parameter Sets (APS's) at an encoder side or parsing the ALF filter sets in the respective APS's at a decoder side, wherein each APS has a corresponding APS index;
signaling multiple indicators in the slice at the encoder side or parsing the multiple indicators in the slice at the decoder side, wherein the multiple indicators correspond to APS indices of a subset of the APS's, corresponding ALF filter sets of the subset of the APS's being used as temporal ALF filter sets for the slice, and the corresponding ALF filter sets of the subset of the APS's being selectable and switchable at a CTB level of the slice;
identifying a current ALF filter set for the current CTB from the corresponding ALF filter sets of the subset of the APS's;
deriving filtered-reconstructed pixels for the current block by applying the current ALF filter set to the current block; and
providing the filtered-reconstructed pixels for encoding or decoding of the current block.
2. The method of claim 1 , wherein the multiple indicators are signaled in a tile group level.
3. The method of claim 1 , wherein the current ALF filter set for the current CTB is identified according to selection information signaled in the current CTB.
4. The method of claim 1 , wherein the current ALF filter set is applied to all blocks in the current CTB.
5. An apparatus for Adaptive Loop Filter (ALF) processing of reconstructed video, the apparatus comprising one or more electronic circuits or processors arranged to:
receive reconstructed pixels, wherein the reconstructed pixels comprise a current block included in a current Coding Tree Block (CTB) in a slice;
signal ALF filter sets in respective Adaptive Parameter Sets (APS's) at an encoder side or parsing the ALF filter sets in the respective APS's at a decoder side, wherein each APS has a corresponding APS index;
signal multiple indicators in the slice at the encoder side or parsing the multiple indicators in the slice at the decoder side, wherein the multiple indicators correspond to APS indices of a subset of the APS's, corresponding ALF filter sets of the subset of the APS's being used as temporal ALF filter sets for the slice, and the corresponding ALF filter sets of the subset of the APS's being selectable and switchable at a CTB level of the slice;
identify a current ALF filter set for the current CTB from the corresponding ALF filter sets of the subset of the APS's;
derive filtered-reconstructed pixels for the current block by applying the current ALF filter set to the current block; and
provide the filtered-reconstructed pixels for encoding or decoding of the current block.
6. The apparatus of claim 5 , wherein the current ALF filter set for the current CTB is identified according to selection information signaled in the current CTB.