Patent ID: 11962779
Assignee: LG ELECTRONICS INC.
Field: Audio-visual technology (Electrical engineering)
Classification: CPC H | IPC H

Claim 0:
1. An image decoding method performed by a decoding apparatus, the method comprising:
obtaining residual information from a bitstream;
deriving a position of a last significant coefficient in a current block based on the residual information;
deriving flag information indicating whether a significant coefficient exists in a second region other than a top-left first region of the current block;
deriving transform coefficients for the current block;
parsing a multiple transform selection (MTS) index from the bitstream based on the flag information indicating that no significant coefficient exists in the second region; and
deriving residual samples for the current block by applying an inverse primary transform to transform coefficients in the first region based on the MTS index,
wherein the deriving of the flag information comprises:
parsing a flag related to whether a significant coefficient is present in a scan subblock by scanning the scan subblock in a preset scan subblock unit according to an reverse diagonal scan order;
determining whether the scan subblock belongs to the second region based on a value of the flag being 1,
determining whether a color index of the current block indicates a luma component based on the scan subblock belonging to the second region; and
wherein the flag information specifies that the significant coefficient is present in the second region based on the color index indicating the luma component.