Image encoding/decoding method and device using palette mode, and method for transmitting bitstream

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

• based on a palette mode applying for a current block, constructing a palette predictor for the current block and constructing a palette table for the current block based on the palette predictor;
• generating a palette index map for the current block based on the palette table;
• and
• encoding the current block based on the palette index map,
• wherein whether the palette mode applies for the current block is determined based on a split structure of the current block being a local dual tree structure,
• wherein whether the split structure of the current block is the local dual tree structure is determined based on at least one of a tree type of the current block and a split structure of a coding tree unit (CTU) including the current block,
• wherein the local dual tree structure is a split structure in which additional splitting is performed only for a luma block within a CTU that has been split into a single tree structure.

A method for transmitting a bitstream generated by an image encoding method, the image encoding method comprising:

• based on a palette mode applying for a current block, constructing a palette predictor for the current block and constructing a palette table for the current block based on the palette predictor;
• generating a palette index map for the current block based on the palette table;
• and
• encoding the current block based on the palette index map,
• whether the palette mode applies for the current block is determined based on a split structure of the current block being a local dual tree structure,
• wherein whether the split structure of the current block is the local dual tree structure is determined based on at least one of a tree type of the current block and a split structure of a coding tree unit (CTU) including the current block,
• wherein the local dual tree structure is a split structure in which additional splitting is performed only for a luma block within a CTU that has been split into a single tree structure.