Method and apparatus for non-linear adaptive loop filtering 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, wherein the reconstructed pixels comprise a current block;
• determine one or more clipping values for the ALF processing, wherein a target clipping value is always signaled at an encoder side or parsed at a decoder side even if the target clipping value is zero;
• derive a current ALF output for the current block, wherein the current ALF output comprises a weighted sum of clipped differences of original differences and each of the original differences is calculated between a first reconstructed pixel at a non-center filter location and a center reconstructed pixel at a center filter location, and wherein each of the original differences is clipped according to a corresponding clipping value to form one clipped difference;
• and
• provide filtered-reconstructed pixels, wherein the filtered-reconstructed pixels comprise the current ALF output.

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;
• determining one or more clipping values for the ALF processing, wherein said one or more clipping values are encoded at an encoder side or decoded at a decoder side using a fixed-length code;
• deriving a current ALF output for the current block, wherein the current ALF output comprises a weighted sum of clipped differences of original differences and each of the original differences is calculated between a first reconstructed pixel at a non-center filter location and a center reconstructed pixel at a center filter location, and wherein each of the original differences is clipped according to a corresponding clipping value to form one clipped difference;
• and
• providing filtered-reconstructed pixels, wherein the filtered-reconstructed pixels comprise the current ALF output.

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;
• determine one or more clipping values for the ALF processing, wherein said one or more clipping values are encoded at an encoder side or decoded at a decoder side using a fixed-length code;
• derive a current ALF output for the current block, wherein the current ALF output comprises a weighted sum of clipped differences of original differences and each of the original differences is calculated between a first reconstructed pixel at a non-center filter location and a center reconstructed pixel at a center filter location, and wherein each of the original differences is clipped according to a corresponding clipping value to form one clipped difference;
• and
• provide filtered-reconstructed pixels, wherein the filtered-reconstructed pixels comprise the current ALF output.