A method and an image processing apparatus for video coding are provided. The method is adapted to the image processing apparatus and includes following steps. A current coding unit is received, and filter selection is performed according to a size of the current coding unit. At least one selected filter is used to perform a filtering operation on a plurality of reference boundaries of the current coding unit to generate a plurality of filtering reference values. An interpolation operation is performed on the current coding unit according to the filtering reference values to generate a plurality of interpolated prediction values.