Video encoding method and device involving intra prediction, and video decoding method and device

1. A video decoding method comprising:

determining reference intra prediction modes, based on availability and prediction modes of adjacent blocks of a current block;

determining candidate intra prediction modes for the current block, based on the reference intra prediction mode;

obtaining, from a bitstream, candidate intra prediction flag indicating whether one of the candidate intra prediction modes is selected as an intra prediction mode of the current block;

when the candidate intra prediction flag indicates that one of the candidate intra prediction modes is selected as the intra prediction mode of the current block, obtaining, from the bitstream, current intra prediction information indicating the intra prediction mode of the current block from among the candidate intra prediction modes; and

selecting the intra prediction mode of the current block from among the candidate intra prediction modes according to the current intra prediction information; and

performing intra prediction on the current block, according to the intra prediction mode of the current block,

wherein,

the determining the reference intra prediction modes includes:

determining a first intra prediction mode of the current block based on a left adjacent block of the current block; and

determining a second intra prediction mode of the current block based on an upper adjacent block of the current block, and

the determining the candidate intra prediction modes includes:

determining a bilinear mode and a DC mode as the candidate intra prediction modes, where the first intra prediction mode and the second intra prediction mode are identical and the first intra prediction mode is the DC mode,

determining the first intra prediction mode and the DC mode as the candidate intra prediction modes, where the first intra prediction mode and the second intra prediction mode are identical and the first intra prediction mode is not the DC mode.

2. The video decoding method of claim 1 , wherein

the reference intra prediction mode comprises the first reference intra prediction mode and the second reference intra prediction mode, wherein the first reference intra prediction mode is determined based on availability and a prediction mode of the left adjacent block of the current block, and the second reference intra prediction mode is determined based on availability and a prediction mode of the above adjacent block of the current block, and

the determining of the reference intra prediction mode comprises

when the left adjacent block of the current block is not present or the left adjacent block of the current block is predicted based on inter prediction, determining the first reference intra prediction mode as the DC mode,

when the left adjacent block of the current block is predicted based on intra prediction, determining the first reference intra prediction mode as an intra prediction mode of the left adjacent block of the current block,

when the above adjacent block of the current block is not present or the above adjacent block of the current block is predicted based on inter prediction, determining the second reference intra prediction mode as the DC mode, and

when the above adjacent block of the current block is predicted based on intra prediction, determining the second reference intra prediction mode as an intra prediction mode of the above adjacent block of the current block.

3. The video decoding method of claim 2 , wherein, when the first reference intra prediction mode and the second reference intra prediction mode are different,

the determining of the candidate intra prediction modes comprises

determining a first candidate intra prediction mode as an intra prediction mode having a smaller index value among the candidate intra prediction modes, and

determining a second candidate intra prediction mode as an intra prediction mode having a larger index value among the candidate intra prediction modes.

4. A video decoding apparatus comprising:

a candidate intra prediction mode determiner configured to

determine reference intra prediction modes, based on availability and prediction modes of adjacent blocks of a current block, and

determine candidate intra prediction modes for the current block, based on the reference intra prediction mode; and

an intra predictor configured to

obtain, from a bitstream, candidate intra prediction flag indicating whether one of the candidate intra prediction modes is selected as an intra prediction mode of the current block, when the candidate intra prediction flag indicates that one of the candidate intra prediction modes is selected as the intra prediction mode of the current block, obtaining, from the bitstream, current intra prediction information indicating the intra prediction mode of the current block from among the candidate intra prediction modes,

select the intra prediction mode of the current block, from among the candidate intra prediction modes according to the current intra prediction information, and

perform intra prediction on the current block, according to the intra prediction mode of the current block,

wherein,

the determining the reference intra prediction modes includes:

determining a first intra prediction mode of the current block based on a left adjacent block of the current block; and

determining a second intra prediction mode of the current block based on an upper adjacent block of the current block, and

the determining the candidate intra prediction modes includes:

determining a bilinear mode and a DC mode as the candidate intra prediction modes, where the first intra prediction mode and the second intra prediction mode are identical and the first intra prediction mode is the DC mode,

determining the first intra prediction mode and the DC mode as the candidate intra prediction modes, where the first intra prediction mode and the second intra prediction mode are identical and the first intra prediction mode is not the DC mode.

5. The video decoding apparatus of claim 4 , wherein

the reference intra prediction mode comprises the first reference intra prediction mode and the second reference intra prediction mode, wherein the first reference intra prediction mode is determined based on availability and a prediction mode of the left adjacent block of the current block, and the second reference intra prediction mode is determined based on availability and a prediction mode of the above adjacent block of the current block, and

the candidate intra prediction mode determiner is further configured to

when the left adjacent block of the current block is not present or the left adjacent block of the current block is predicted based on inter prediction, determining the first reference intra prediction mode as the DC mode,

when the left adjacent block of the current block is predicted based on intra prediction, determining the first reference intra prediction mode as an intra prediction mode of the left adjacent block of the current block,

when the above adjacent block of the current block is not present or the above adjacent block of the current block is predicted based on inter prediction, determining the second reference intra prediction mode as the DC mode, and

when the above adjacent block of the current block is predicted based on intra prediction, determining the second reference intra prediction mode as an intra prediction mode of the above adjacent block of the current block.

6. The video decoding apparatus of claim 5 , wherein, when the first reference intra prediction mode and the second reference intra prediction mode are different,

the candidate intra prediction mode determiner is further configured to

determine a first candidate intra prediction mode as an intra prediction mode having a smaller index value among the candidate intra prediction modes, and

determine a second candidate intra prediction mode as an intra prediction mode having a larger index value among the candidate intra prediction modes.

7. A video encoding method comprising:

determining reference intra prediction modes, based on availability and prediction modes of adjacent blocks of a current block;

determining candidate intra prediction modes for the current block, based on the reference intra prediction mode; and

based on an intra prediction mode of the current block and the plurality of candidate intra prediction modes of the current block, determining candidate intra prediction flag indicating whether the current block is predicted according to one of the candidate intra prediction modes, and current intra prediction information indicating the intra prediction mode of the current block from among the candidate intra prediction modes; and

outputting a bitstream including the candidate intra prediction flag and the current intra prediction information,

wherein,

the determining the reference intra prediction modes includes:

determining a first intra prediction mode of the current block based on a left adjacent block of the current block; and

determining a second intra prediction mode of the current block based on an upper adjacent block of the current block, and

the determining the candidate intra prediction modes includes:

determining a bilinear mode and a DC mode as the candidate intra prediction modes, where the first intra prediction mode and the second intra prediction mode are identical and the first intra prediction mode is the DC mode,

determining the first intra prediction mode and the DC mode as the candidate intra prediction modes, where the first intra prediction mode and the second intra prediction mode are identical and the first intra prediction mode is not the DC mode.