Video coding method and device which use sub-block unit intra prediction

An image decoding method performed by an image decoding apparatus, the method comprising:

• dividing one coding unit into a plurality of sub-blocks;
• and sequentially performing intra prediction on each of the sub-blocks,
• wherein in the performing of the intra prediction, reference sample buffers used for intra prediction of the respective sub-blocks are differently constructed.

An image decoding method performed by an image decoding apparatus, the method comprising:

• dividing one coding unit into a plurality of sub-blocks;
• sequentially performing intra prediction on each of the sub-blocks,
• wherein when constructing a reference sample buffer for intra prediction for each of the sub-blocks, one or more reconstructed samples of one or more sub-blocks spatially adjacent to a target sub-block to be decoded, of the plurality of sub-blocks, are used as one or more reference samples.

An image decoding apparatus comprising an inter prediction unit and an intra prediction unit,

• wherein the intra prediction unit determines whether to perform sub-block-based intra prediction on a current coding unit, performs intra prediction on each of sub-blocks of the current coding unit, when information indicating whether to perform sub-block-based intra prediction has a value of “true”, and performs block-based intra prediction on the current coding unit when the information indicating whether to perform sub-block-based intra prediction has a value of “false”.

An image decoding apparatus comprising an intra prediction unit and a reconstructed picture buffer, the intra prediction unit performing sub-block-based intra prediction on one coding unit,

• wherein the intra prediction unit sequentially performs intra prediction on each of the sub-blocks by constructing different reference sample buffers for the respective sub-blocks, and wherein among reconstructed samples stored in the reconstructed picture buffer, some reconstructed samples of one or more sub-blocks spatially adjacent to a target sub-block to be decoded are used as reference samples to construct the reference sample buffer for the target sub-block.