Method and device for coding/decoding image using intra prediction
A method and a device for encoding/decoding an image according to the present invention may determine a reference region for intra prediction of a current block, derive an intra prediction mode of the current block on the basis of a predetermined MPM candidate group, and perform intra prediction on the current block on the basis of the reference region and the intra prediction mode.
1 . A method of decoding an image, comprising:
determining a reference pixel line among a plurality of pixel lines for intra prediction of a current block;
determining a first flag indicating whether an intra prediction mode of the current block is selected from an MPM (Most Probable Mode) candidate group;
when the first flag indicates that the intra prediction mode of the current block is selected from the MPM candidate group, determining a second flag indicating whether an intra prediction mode of the current block is derived from a first MPM group or a second MPM group, wherein the MPM candidate group is divided into the first MPM group comprising one or more default intra prediction modes and the second MPM group comprising one or more non-default intra prediction modes that are derived from an intra prediction mode of a neighboring block adjacent to the current block;
when the second flag is determined to be a first value, deriving an intra prediction mode of the current block based on a default intra prediction mode in the first MPM group;
when the second flag is determined to be a second value, deriving the intra prediction mode of the current block based on a non-default intra prediction mode in the second MPM group that is selected by an MPM index; and
performing the intra prediction on the current block based on the reference pixel line and the intra prediction mode,
wherein the plurality of pixel lines at least include a first pixel line immediately adjacent to the current block, a second pixel line immediately adjacent to the first pixel line, and a third pixel line immediately adjacent to the second pixel line, and
wherein the second flag is determined by parsing a bitstream only when the reference pixel line of the current block is determined to be the first pixel line.
2 . The method of claim 1 , wherein the default MPM mode is composed of only a non-directional mode, and
wherein the non-directional mode includes at least one of a planar mode or a DC mode.
3 . The method of claim 2 , wherein the second MPM group further includes a mode derived by adding or subtracting an N value to the intra prediction mode of the neighboring block, and
wherein the N value is 1, 2, or 3.
4 . The method of claim 1 , further comprising:
dividing the current block into a plurality of sub-blocks,
wherein the intra prediction is performed in units of the sub-blocks, and
wherein the number of the sub-blocks is variably determined based on a size or a shape of the current block.
5 . The method of claim 1 , wherein the second flag is determined to be the second value when the reference pixel line of the current block is determined not to be the first pixel line.
6 . A method of encoding an image, comprising:
determining a reference pixel line among a plurality of pixel lines for intra prediction of a current block;
determining an intra prediction mode of the current block;
performing the intra prediction on the current block based on the reference pixel line and the intra prediction mode; and
determining a first flag indicating whether an intra prediction mode of the current block is in an MPM (Most Probable Mode) candidate group; and
when the intra prediction mode of the current block is in the MPM candidate group, determining, based on the intra prediction mode of the current block, a second flag indicating whether the intra prediction mode of the current block is derived from a first MPM group or a second MPM group, wherein the MPM candidate group is divided into the first MPM group comprising one or more default intra prediction modes and the second MPM group comprising one or more non-default intra prediction modes that are derived from an intra prediction mode of a neighboring block adjacent to the current block;
wherein the plurality of pixel lines at least include a first pixel line immediately adjacent to the current block, a second pixel line immediately adjacent to the first pixel line, and a third pixel line immediately adjacent to the second pixel line, and
wherein the second flag is encoded into a bitstream only when the reference pixel line of the current block is determined to be the first pixel line, and
wherein the second flag is determined to be a first value, when the intra prediction mode of the current block is a default intra prediction mode in the first MPM group,
wherein the second flag is determined to be a second value, when the intra prediction mode of the current block is a non-default intra prediction mode in the second MPM group,
wherein an MPM index indicating one among non-default intra prediction modes in the second MPM group is encoded into the bitstream, when the second flag is determined to be the second value.
7 . A method of transmitting a bitstream, the method comprising:
transmitting the bitstream generated by a method of encoding an image to an image decoding apparatus,
wherein the method of encoding an image comprises
determining a reference pixel line among a plurality of pixel lines for intra prediction of a current block;
determining an intra prediction mode of the current block;
performing the intra prediction on the current block based on the reference pixel line and the intra prediction mode; and
determining a first flag indicating whether an intra prediction mode of the current block is in an MPM (Most Probable Mode) candidate group; and
when the intra prediction mode of the current block is in the MPM candidate group, determining, based on the intra prediction mode of the current block, a second flag indicating whether the intra prediction mode of the current block is derived from a first MPM group or a second MPM group, wherein the MPM candidate group is divided into the first MPM group comprising one or more default intra prediction modes and the second MPM group comprising one or more non-default intra prediction modes that are derived from an intra prediction mode of a neighboring block adjacent to the current block;
wherein the plurality of pixel lines at least include a first pixel line immediately adjacent to the current block, a second pixel line immediately adjacent to the first pixel line, and a third pixel line immediately adjacent to the second pixel line, and
wherein the second flag is encoded into a bitstream only when the reference pixel line of the current block is determined to be the first pixel line, and
wherein the second flag is determined to be a first value, when the intra prediction mode of the current block is a default intra prediction mode in the first MPM group,
wherein the second flag is determined to be a second value, when the intra prediction mode of the current block is a non-default intra prediction mode in the second MPM group,
wherein an MPM index indicating one among non-default intra prediction modes in the second MPM group is encoded into the bitstream, when the second flag is determined to be the second value.