Method and apparatus for processing video signal
A method for decoding an image according to the present invention comprises the steps of: deriving an intra prediction mode of a current block; and changing the intra prediction mode to a wide angle intra prediction mode when the intra prediction mode is less than or equal to a threshold value and the current block is a non-square having a width greater than a height.
1. A method of decoding an image, comprising:
determining a reference sample line index of a current block in the image, the reference sample line index indicating one of a plurality of reference sample lines pre-defined in a decoding apparatus;
deriving an intra prediction mode of the current block based on an MPM (Most Probable Mode) flag decoded from a bitstream; and
performing intra prediction on the current block based on the intra prediction mode and at least one of reference samples in a reference sample line indicated by the reference sample line index,
wherein, in response to the MPM flag being equal to a first value, the intra prediction mode of the current block is derived from MPM candidates or a default mode,
wherein, in response to the MPM flag being equal to a second value, the intra prediction mode of the current block is not derived from the MPM candidates and the default mode,
wherein, in response to the MPM flag being equal to the first value, a default mode flag is further decoded from the bitstream, the default mode flag indicating whether the intra prediction mode of the current block is set equal to the default mode,
wherein the default mode is representative of a Planar mode, and
wherein, in response to the reference sample line index being greater than a pre-defined value, the MPM flag is not decoded from the bitstream and a value of the MPM flag is inferred to the first value.
2. The method of claim 1 , wherein the plurality of reference sample lines includes a neighboring reference sample line and one or more non-neighboring reference sample lines to the current block.
3. The method of claim 2 , wherein a number of reference sample lines available for the current block is adaptively determined based on whether the current block is located on a boundary of a coding tree unit.
4. The method of claim 3 , wherein, in response to the current block being located on the boundary of the coding tree unit, the number of reference sample lines available for the current block is 1, and
wherein, in response to the current block being not located on the boundary of the coding tree unit, the number of reference sample lines available for the current block is 3.
5. The method of claim 1 , wherein, in response to the default mode flag indicating that the intra prediction mode of the current block is not set equal to the default mode, the intra prediction mode of the current block is determined based on an MPM candidate indicated by an MPM index among the MPM candidates.
6. A method of encoding an image, comprising:
determining a reference sample line index of a current block in the image, the reference sample line index indicating one of a plurality of reference sample lines pre-defined in an encoding apparatus;
determining an intra prediction mode of the current block;
obtaining a residual block of the current block based on an original block of the current block and a prediction block of the current block, the prediction block being obtained by performing intra prediction on the current block based on the intra prediction mode and at least one of reference samples in a reference sample line indicated by the reference sample line index; and
encoding the residual block of the current block to generate a bitstream,
wherein an MPM flag equal to a first value is encoded into the bitstream in response to a case where the intra prediction mode of the current block is derived from the MPM candidates or a default mode,
wherein the MPM flag equal to a second value is encoded into the bitstream in response to a case where the intra prediction mode of the current block is not derived from the MPM candidates and the default mode,
wherein, in response to the MPM flag being equal to the first value, a default mode flag is further encoded into the bitstream, the default mode flag indicating whether the intra prediction mode of the current block is set equal to the default mode,
wherein the default mode is representative of a Planar mode, and
wherein, in response to the reference sample line index being greater than a pre-defined value, the MPM flag is not encoded into the bitstream and a value of the MPM flag is inferred to the first value.
7. A non-transitory computer readable medium having stored thereon a compressed image data, the compressed image data comprising at least one of:
a reference sample line index indicating one of a plurality of pre-defined reference sample lines or an MPM (Most Probable Mode) flag indicating whether an intra prediction mode of the current block is derived from MPM candidates,
wherein, in response to the MPM flag being equal to a first value, the intra prediction mode of the current block is derived from the MPM candidates or a default mode,
wherein, in response to the MPM flag being equal to a second value, the intra prediction mode of the current block is not derived from the MPM candidates and the default mode,
wherein, in response to the MPM flag being equal to the first value, the compressed video data further comprises a default mode flag indicating whether the intra prediction mode of the current block is set equal to the default mode,
wherein the default mode is representative of a Planar mode, and
wherein, in response to the reference sample line index being greater than a pre-defined value, the MPM flag is not comprised in the compressed video data and a value of the MPM flag is inferred to the first value.