Image encoding/decoding methods and apparatuses
Image encoding/decoding methods and apparatuses according to the present invention may generate a prediction block of a current block based on a pre-defined prediction mode, generate a transform block of the current block through predetermined transformation, and reconstruct the current block based on the prediction block and the transform block.
1. A method of decoding an image, the method comprising:
determining an intra prediction mode of a current block in the image based on a syntax element obtained from a bitstream;
generating a prediction block of the current block by performing intra prediction of the current block based on the intra prediction mode; and
reconstructing the current block based on the prediction block,
wherein the syntax element comprises a flag indicating whether a pre-defined mode is used for the intra prediction of the current block,
wherein, in response to the flag indicating that the pre-defined mode is used for the intra prediction of the current block, the intra prediction mode is set to the pre-defined mode,
wherein, in response to the flag indicating that the pre-defined mode is not used for the intra prediction of the current block, the intra prediction mode is derived from a candidate group including a plurality of most probable mode (MPM) candidates, and
wherein the pre-defined mode is representative of a Planar mode.
2. The method of claim 1 , wherein the pre-defined mode is not included in the candidate group.
3. The method of claim 2 , wherein the plurality of MPM candidates comprises at least one of an intra prediction mode of a surrounding block (candIntraPredMode), (candIntraPredMode−N), or (candIntraPredMode+N), and
wherein N is equal to 2.
4. The method of claim 2 , wherein the plurality of MPM candidates comprises at least one of a DC mode, a vertical mode, a horizontal mode, (the vertical mode-M), or (the vertical mode+M), and
wherein M is equal to 4.
5. The method of claim 1 , wherein, in response to the intra prediction mode being a directional mode, the intra prediction mode is modified by adding or subtracting a predetermined offset,
wherein the intra prediction is performed using the modified intra prediction mode, and
wherein the modification of the intra prediction mode is selectively performed based on at least one of a size, a shape, partition information, a value of the intra prediction mode, or a component type of the current block.
6. The method of claim 1 , wherein performing the intra prediction comprises:
partitioning the current block into a plurality of sub-blocks by using a vertical line or a horizontal line; and
sequentially performing the intra prediction in units of the sub-blocks,
wherein a number of the sub-blocks belonging to the current block is variably determined based on at least one of a size or a shape of the current block.
7. The method of claim 1 , wherein performing the intra prediction comprising:
modifying a prediction value, generated by performing the intra prediction, based on a predetermined reference sample and a weight.
8. The method of claim 7 , wherein each of the reference sample and the weight is determined based on at least one of a size of the current block, a position of a current sample to be modified, or the intra prediction mode of the current block.
9. The method of claim 1 , wherein, in response to a case where the pre-defined mode is used for the intra prediction of the current block, an intra reference line for the intra prediction is restricted to be determined as only a reference line adjacent to the current block among a plurality of reference lines.
10. A method of encoding an image, the method comprising:
determining an intra prediction mode of a current block in the image;
generating a prediction block of the current block by performing intra prediction of the current block; and
obtaining a residual block of the current block based on the prediction block,
wherein a prediction block of the current block is generated by performing the intra prediction based on the intra prediction mode of the current block,
wherein a flag indicating whether a pre-defined mode is used for the intra prediction of the current block is encoded into a bitstream,
wherein, in response to a case where the pre-defined mode is used for the intra prediction of the current block, the intra prediction mode is determined to be the pre-defined mode,
wherein, in response to a case where the pre-defined mode is not used for the intra prediction of the current block, the intra prediction mode is determined from a candidate group including a plurality of most probable mode (MPM) candidates, and
wherein the pre-defined mode is representative of a Planar mode.
11. A non-transitory computer-readable storage medium for storing a bitstream generated by an image encoding method,
the image encoding method comprising:
determining an intra prediction mode of a current block;
generating a prediction block of the current block by performing intra prediction of the current block; and
obtaining a residual block of the current block based on the prediction block,
wherein a prediction block of the current block is generated by performing the intra prediction based on the intra prediction mode of the current block,
wherein a flag indicating whether a pre-defined mode is used for the intra prediction of the current block is encoded into a bitstream,
wherein, in response to a case where the pre-defined mode is used for the intra prediction of the current block, the intra prediction mode is determined to be the pre-defined mode,
wherein, in response to a case where the pre-defined mode is not used for the intra prediction of the current block, the intra prediction mode is determined from a candidate group including a plurality of MPM candidates, and
wherein the pre-defined mode is representative of a Planar mode.