Systems and methods for applying adaptive loop filters in video coding

Abstract

A device may be configured to apply adaptive loop filters according to one or more of the techniques described herein.

1 . A method of filtering a chroma coding tree block and modifying a reconstructed sample value, the method comprising:
 inputting a reconstructed chroma picture sample array, a chroma location of top-left of a current chroma coding tree block, and a chroma filter index;   determining chroma filter coefficients by using the chroma filter index;   determining a variable applyAlfLineBufBoundary based on whether or not a bottom boundary of a current coding tree block is a bottom boundary of a picture;   determining a current reconstructed sample value curr by using the reconstructed chroma picture sample array;   determining a variable alfShiftC for a shift operation according to a vertical position of a chroma sample and the variable applyAlfLineBufBoundary;   determining a sum value S by using the chroma filter coefficients, the reconstructed chroma picture sample array and the current reconstructed sample value curr;   determining a modified sum value being equivalent to a value of MS in the following equation,
   MS=curr +(( S +variable offset) >>alfShiftC), 
   wherein the variable offset is derived according to the variable alfShiftC; and   calculating a modified reconstructed sample value by using the modified sum value.   
     
     
         2 . A device comprising one or more processors configured to:
 input a reconstructed chroma picture sample array, a chroma location of top-left of a current chroma coding tree block, and chroma filter index;   determine chroma filter coefficients by using the chroma filter index;   determine a variable applyAlfLineBufBoundary based on whether or not a bottom boundary of a current coding tree block is a bottom boundary of a picture;   determine a current reconstructed sample value curr by using the reconstructed chroma picture sample array;   determine a variable alfShiftC for a shift operation according to a vertical position of a chroma sample and the variable applyAlfLineBufBoundary;   determine a sum value S by using the chroma filter coefficients, the reconstructed chroma picture sample array and the current reconstructed sample value curr;   determine a modified sum value being equivalent to a value of MS in the following equation,
   MS=curr+(( S +variable offset)>>alfShiftC), 
   wherein the variable offset is derived according to the variable alfShiftC; and   calculate a modified reconstructed sample value by using the modified sum value.