Patent ID: 11936911
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 prediction information and information on quantized transform coefficients from a bitstream;
deriving quantized transform coefficients for a target block based on the information on the quantized transform coefficients;
deriving transform coefficients for the target block based on a dequantization for the quantized transform coefficients;
deriving modified transform coefficients for the target block based on an inverse secondary transform for the transform coefficients;
deriving residual samples for the target block based on an inverse primary transform for the modified transform coefficients;
deriving prediction samples for the target block based on the prediction information; and
generating a reconstructed picture based on the residual samples and the prediction samples for the target block,
wherein the deriving of the modified transform coefficients comprises:
deriving a transform kernel matrix, and
performing a matrix operation of the transform coefficients and the transform kernel matrix,

wherein the transform kernel matrix is derived based on a transform index and a transform set,
wherein the transform index represents at least one of first index information, second index information, and third index information, the first index information indicating the inverse secondary transform being not applied to the target block, the second index information indicating a first transform kernel matrix as the transform kernel matrix for the inverse secondary transform, and the third index information indicating a second transform kernel matrix as the transform kernel matrix for the inverse secondary transform,
wherein the transform set is determined based on an intra prediction mode of the target block,
wherein the intra prediction mode of the target block is mapped to one of the four transform sets,
wherein the transform set is determined, based on the intra prediction mode being equal to 0 or 1, as a first transform set index value,
wherein the transform set is determined, based on the intra prediction mode being greater than or equal to 2 and smaller than or equal to 12, as a second transform set index value,
wherein the transform set is determined, based on the intra prediction mode being greater than or equal to 13 and smaller than or equal to 23, as a third transform set index value,
wherein the transform set is determined, based on the intra prediction mode being greater than or equal to 24 and smaller than or equal to 44, as a fourth transform set index value,
wherein the transform set is determined, based on the intra prediction mode being greater than or equal to 45 and smaller than or equal to 55, as the third transform set index value, and
wherein the transform set is determined, based on the intra prediction mode being greater than or equal to 56, as the second transform set index value.