Video coding method and device which use sub-block unit intra prediction
The present invention relates to an intra prediction scheme among video coding techniques and, more particularly, relates to a video decoding method and apparatus for diving a block into a plurality of sub-blocks when intra prediction is performed and sequentially performing infra prediction on each of the sub-blocks. The decoding method performed by a video decoding apparatus includes determining whether to perform sub-block-based intra prediction on a current coding unit, dividing the current coding unit into a plurality of sub-blocks, performing intra prediction on each of the sub-blocks when a result of determination of whether to perform sub-block-based intra prediction has a value of “true”, and directly performing block-based intra prediction on the current coding unit without dividing the current coding unit when the result of the determination has a value of “false”.
1. An image decoding method performed by an image decoding apparatus, the method comprising:
determining whether to perform block-based intra prediction or sub-block-based intra prediction on a current block;
generating a prediction signal of the current block based on the block-based intra prediction or the sub-block-based intra prediction; and
reconstructing the current block based on the prediction signal,
wherein, in response to the sub-block-based intra prediction, the prediction signal of the current block is generated by performing intra prediction on each of sub-blocks resulting from dividing the current block in at least one of a vertical direction or a horizontal direction,
wherein, in response to the size of the current block being 8×4, a number of the sub-blocks resulting from dividing the current block is N,
wherein, in response to the size of the current block being 16×4, the number of the sub-blocks resulting from dividing the current block is 2N, and
wherein N is representative of a multiple of 2.
2. The method according to claim 1 , wherein the sub-block-based intra prediction is performed based on the size of the current block being less that or equal to a size of a maximum unit that allows the sub-block-based intra prediction.
3. The method according to claim 2 , wherein, in response to the size of the current block being 8×4, a width of the current block is divided by 2 to obtain the sub-blocks having a width equal to 4, and
wherein, in response to the size of the current block being 16×4, the width of the current block is divided by 4 to obtain the sub-blocks having a width equal to 4.
4. The method according to claim 3 , wherein the intra prediction on the each of sub-blocks is sequentially performed according to a predetermined order.
5. The method according to claim 1 , wherein reference samples for the block-based intra prediction are defined using the width and the height of the current block, and
wherein reference samples for the sub-block-based intra prediction are defined using a width and a height of a sub-block included in the current block.
6. The method according to claim 1 , wherein the current block is obtained by dividing a coding block according to a multi-type partitioning, the multi-type partitioning including at least one of a binary partitioning or a triple partitioning.
7. The method according to claim 6 , wherein the triple-tree partitioning is a block partitioning structure of dividing one coding block into three coding blocks based on two split lines.
8. The method according to claim 7 , wherein the two split lines cross a center position of the one coding block,
wherein a size of one of the three coding blocks is greater than a size of the other two of the three coding blocks, and
wherein the other two of the three coding blocks have the same size.
9. The method of claim 8 , wherein the size of the one of the three coding blocks is twice the size of the other two of the three coding blocks.
10. An image encoding method performed by an image encoding apparatus, the method comprising:
determining whether to perform block-based intra prediction or sub-block-based intra prediction on a current block;
obtaining a residual signal of the current block, the residual signal being a difference between a prediction signal and an original signal of the current block, the prediction signal being obtained based on the block-based intra prediction or the sub-block-based intra prediction; and
generating a bitstream by encoding the residual signal of the current block,
wherein, in response to the sub-block-based intra prediction, the prediction signal of the current block is generated by performing intra prediction on each of sub-blocks resulting from dividing the current block in at least one of a vertical direction or a horizontal direction,
wherein, in response to the size of the current block being 8×4, a number of the sub-blocks resulting from dividing the current block is N,
wherein, in response to the size of the current block being 16×4, the number of the sub-blocks resulting from dividing the current block is 2N, and
wherein N is representative of a multiple of 2.
11. A transmission method of a video signal, comprising:
determining whether to perform block-based intra prediction or sub-block-based intra prediction on a current block;
obtaining a residual signal of the current block, the residual signal being a difference between a prediction signal and an original signal of the current block, the prediction signal being obtained based on the block-based intra prediction or the sub-block-based intra prediction;
generating a bitstream by encoding the residual signal of the current block; and
transmitting the bitstream associated with the video signal,
wherein, in response to the sub-block-based intra prediction, the prediction signal of the current block is generated by performing intra prediction on each of sub-blocks resulting from dividing the current block in at least one of a vertical direction or a horizontal direction,
wherein, in response to the size of the current block being 8×4, a number of the sub-blocks resulting from dividing the current block is N,
wherein, in response to the size of the current block being 16×4, the number of the sub-blocks resulting from dividing the current block is 2N, and
wherein N is representative of a multiple of 2.