Method and device for intra-prediction

An image encoding method performed by an image encoding apparatus, comprising:

• determining that multi-sample prediction is applied to a current block based on an intra prediction mode of the current block, the current block being a prediction unit to which the intra prediction mode is applied;
• determining a representative prediction value for a sample group, the sample group being a region inside the current block, being smaller than the current block, and being predicted as the same representative prediction value;
• predicting a plurality of samples included in the sample group using the determined representative prediction value;
• generating a prediction block of the current block based on the determined representative prediction value;
• generating a residual block of the current block based on the prediction block;
• and
• generating a transform coefficient for the residual block of the current block,
• wherein the representative prediction value is determined as an average value of a plurality of reference samples,
• wherein other samples inside the current block which are not included in the sample group are predicted differently from the plurality of samples included in the sample group,
• wherein the multi-sample prediction is performed based on a determination of whether the size of the current block is less than 32×32.

A non-transitory computer-readable recording medium storing a bitstream which is received and decoded by an image decoding apparatus and used to reconstruct an image,

• wherein the bitstream comprises information on an intra prediction mode of a current block and information on a residual block of the current block;
• the information on an intra prediction mode of the current block is used to generate an intra prediction mode of the current block;
• the intra prediction mode of the current block is used to determine that multi-sample prediction is applied to the current block, the current block being a prediction unit to which the intra prediction mode is applied;
• wherein a representative prediction value for a sample group is determined, the sample group being a region inside the current block, being smaller than the current block, and being predicted as the same representative prediction value;
• the determined representative prediction value is used to predict a plurality of samples included in the sample group and to generate a prediction block of the current block;
• the information on the residual block of the current block comprises information on a transform coefficient for a residual block of the current block which is used to generate the residual block of the current block;
• wherein the representative prediction value is determined as an average value of a plurality of reference samples,
• wherein other samples inside the current block which are not included in the sample group are predicted differently from the plurality of samples included in the sample group, and
• wherein the multi-sample prediction is performed based on a determination of whether the size of the current block is less than 32×32.