Image encoding/decoding method and apparatus based on palette mode, and recording medium that stores bitstream

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

obtaining palette prediction information and palette index information of a current block from a bitstream;

constructing a palette table for the current block based on the palette prediction information;

generating a palette index map for the current block based on the palette index information; and

decoding the current block based on the palette table and the palette index map,

wherein the palette prediction information comprises run-value information specifying a first palette entry reused in the palette table among palette entries in a palette predictor for the current block,

wherein the run-value information is obtained from the bitstream based on an index value of the first palette entry being smaller than a first size of the palette predictor and maximum size information for the palette predictor without size information for the palette predictor,

wherein, based on only a value of the run-value information being greater than 1, a value related to a palette predictor is updated,

wherein, based on the run-value information having a value of 1, search of the first palette entry is terminated.

2 . The image decoding method of claim 1 , wherein the index value of the first palette entry is determined based on the run-value information.

3 . The image decoding method of claim 1 , wherein the first size specifies the number of palette entries determined based on a palette table for a block decoded before the current block.

4 . The image decoding method of claim 1 , wherein the first size specifies the number of palette entries determined based on size information of the palette predictor obtained from the bitstream.

5 . The image decoding method of claim 1 , wherein the first size specifies a maximum number of palette entries able to be included in the palette predictor.

6 . The image decoding method of claim 5 , wherein the first size is determined based on a predetermined first flag specifying a split structure of a coding tree unit (CTU) comprising the current block.

7 . The image decoding method of claim 6 , wherein the first size is determined to be 63, based on the first flag having a first value specifying that the current block is included in an I slice and the CTU is split into a single tree structure.

8 . The image decoding method of claim 6 , wherein the first size is determined to be 31, based on the first flag having a second value specifying that the current block is included in an I slice, the CTU is implicit-quadtree-split into a 64×64 luma sample coding unit (CU), and the 64×64 luma sample CU becomes a root node of a dual tree.

9 . The image decoding method of claim 1 , further comprising updating the palette predictor based on the palette table and reuse information of the palette predictor, based on the current block being decoded.

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

constructing a palette table for a current block based on a palette predictor for the current block;

generating a palette index map for the current block based on the palette table;

encoding the current block based on the palette index map; and

generating a bitstream comprising palette prediction information and palette index information of the encoded current block,

wherein the palette prediction information comprises run-value information specifying a first palette entry reused in the palette table among palette entries in the palette predictor for the current block,

wherein the run-value information is encoded in the bitstream based on an index value of the first palette entry being smaller than a maximum size of the palette predictor and maximum size information for the palette predictor without size information for the palette predictor,

wherein, based on only a value of the run-value information being greater than 1, a value related to a palette predictor is updated,

wherein, based on the run-value information having a value of 1, search of the first palette entry is terminated.

11 . The image encoding method of claim 10 , wherein the index value of the first palette entry is determined based on the run-value information.

12 . The image encoding method of claim 10 , wherein the maximum size of the palette predictor is determined to be 63, based on the current block being included in an I slice and a coding tree unit (CTU) comprising the current block being split into a single tree structure.

13 . The image encoding method of claim 10 , wherein the maximum size of the palette predictor is determined to be 31, based on the current block being included in an I slice, a coding tree unit (CTU) including the current block being implicit-quadtree-split into a 64×64 luma sample coding unit (CU), and the 64×64 luma sample CU becoming a root node of a dual tree.

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

constructing a palette table for a current block based on a palette predictor for the current block;

generating a palette index map for the current block based on the palette table;

encoding the current block based on the palette index map; and

generating a bitstream comprising palette prediction information and palette index information of the encoded current block,

wherein the palette prediction information comprises run-value information specifying a first palette entry reused in the palette table among palette entries in the palette predictor for the current block,

wherein the run-value information is encoded in the bitstream based on an index value of the first palette entry being smaller than a maximum size of the palette predictor and maximum size information for the palette predictor without size information for the palette predictor,

wherein, based on only a value of the run-value information being greater than 1, a value related to a palette predictor is updated,

wherein, based on the run-value information having a value of 1, search of the first palette entry is terminated.