Image encoding/decoding method and device, and recording medium in which bitstream is stored

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

deriving an intra prediction mode of a current block using an intra prediction mode of a neighboring block adjacent to the current block;

selecting one reference sample line from among a plurality of reference sample lines adjacent to the current block;

generating reference samples for the current block based on the selected one reference sample line; and

performing intra prediction for the current block using the intra prediction mode and the reference samples,

wherein the performing intra prediction for the current block comprises,

selecting an interpolation filter from among a plurality of interpolation filters; and

filtering the reference samples using the selected interpolation filter,

wherein the interpolation filter is selected based on a size of the current block, and

wherein the size of the current block is derived based on an average of a log value of width of the current block and a log value of a height of the current block.

2. The image decoding method of claim 1 ,

wherein the selecting one interpolation filter from among the plurality of interpolation filters and the filtering the reference samples using the selected interpolation filter is performed in case the intra prediction mode of the current block is a directional mode.

3. The image decoding method of claim 1 ,

wherein, in case the selected one reference sample line is a first reference sample line directly adjacent to the current block, the selecting one interpolation filter from among the plurality of interpolation filters is performed based on the size of the current block.

4. The image decoding method of claim 1 ,

wherein, in case the selected one reference sample line is not a first reference sample line directly adjacent to the current block, a cubic filter is selected as the interpolation filter for filtering the reference samples.

5. The image decoding method of claim 1 , further comprising:

determining whether to perform a secondary filtering for the prediction block of the current block based on at least one among the intra prediction mode of the current block, a size of the current block or the selected one reference sample line;

deriving a scaling value based on the size of the current block in case the secondary filtering is performed;

deriving a filter coefficient of the secondary filtering based on the scaling value; and

generating a filtered prediction block of the current block by performing the secondary filtering for the prediction block based on the derived filter coefficient.

6. An image encoding method performed by an image encoding apparatus, the image encoding method comprising:

determining an intra prediction mode of a current block;

selecting one reference sample line from among a plurality of reference sample lines adjacent to the current block;

generating reference samples for the current block based on the selected one reference sample line;

performing intra prediction for the current block using the intra prediction mode and the reference samples; and

encoding the intra prediction mode of the current block using an intra prediction mode of a neighboring block adjacent to the current block,

wherein the performing intra prediction for the current block comprises,

selecting an interpolation filter from among a plurality of interpolation filters; and

filtering the reference samples using the selected interpolation filter,

wherein the interpolation filter is selected based on a size of the current block, and

wherein the size of the current block is derived based on an average of a log value of width of the current block and a log value of a height of the current block.

7. The image encoding method of claim 6 ,

wherein the selecting one interpolation filter from among the plurality of interpolation filters and the filtering the reference samples using the selected interpolation filter is performed in case the intra prediction mode of the current block is a directional mode.

8. The image encoding method of claim 6 ,

wherein, in case the selected one reference sample line is a first reference sample line directly adjacent to the current block, the selecting one interpolation filter from among the plurality of interpolation filters is performed based on the size of the current block.

9. The image encoding method of claim 6 ,

wherein, in case the selected one reference sample line is not a first reference sample line directly adjacent to the current block, a cubic filter is selected as the interpolation filter for filtering the reference samples.

10. A non-transitory computer readable recording medium storing a bitstream that is generated by an image encoding method, the image encoding method comprising:

determining an intra prediction mode of a current block;

selecting one reference sample line from among a plurality of reference sample lines adjacent to the current block;

generating reference samples for the current block based on the selected one reference sample line;

performing intra prediction for the current block using the intra prediction mode and the reference samples; and

encoding the intra prediction mode of the current block using an intra prediction mode of a neighboring block adjacent to the current block,

wherein the performing intra prediction for the current block comprises,

selecting an interpolation filter from among a plurality of interpolation filters; and

filtering the reference samples using the selected interpolation filter,

wherein the interpolation filter is selected based on a size of the current block, and

wherein the size of the current block is derived based on an average of a log value of width of the current block and a log value of a height of the current block.