A method and apparatus for loop filter processing of boundary pixels across a block boundary aligned with a slice or tile boundary is disclosed. Embodiments according to the present invention use a parameter of a neighboring slice or tile for loop filter processing across slice or tile boundaries according to a flag indicating whether cross slice or tile loop filter processing is allowed not. According to one embodiment of the present invention, the parameter is a quantization parameter corresponding to a neighboring slice or tile, and the quantization parameter is used for filter decision in deblocking filter.