Method and apparatus for signaling adaptive loop filter parameters in video coding

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 in a current picture;
• determine one or more virtual boundaries in the current picture;
• derive filtered-reconstructed pixels for the current picture by applying the ALF process on the current picture, wherein when the ALF processing applied on a target sample among the reconstructed pixels that is on one side of a target virtual boundary requires an outside sample among the reconstructed pixels that is on another side of the target virtual boundary, the ALF processing uses a padded sample in place of the outside sample for applying the ALF processing on the target sample;
• and
• provide the filtered-reconstructed pixels for encoding or decoding of the current picture.