US 12,244,813 B2
Transform-based image coding method and device therefor
Moonmo Koo, Seoul (KR); Seunghwan Kim, Seoul (KR); and Jaehyun Lim, Seoul (KR)
Assigned to LG ELECTRONICS INC., Seoul (KR)
Filed by LG ELECTRONICS INC., Seoul (KR)
Filed on Mar. 20, 2024, as Appl. No. 18/611,275.
Application 18/611,275 is a continuation of application No. 17/572,476, filed on Jan. 10, 2022, granted, now 11,973,951.
Application 17/572,476 is a continuation of application No. PCT/KR2020/009138, filed on Jul. 10, 2020.
Claims priority of provisional application 62/873,898, filed on Jul. 13, 2019.
Claims priority of provisional application 62/873,824, filed on Jul. 12, 2019.
Prior Publication US 2024/0275973 A1, Aug. 15, 2024
This patent is subject to a terminal disclaimer.
Int. Cl. H04N 19/132 (2014.01); H04N 19/159 (2014.01); H04N 19/176 (2014.01); H04N 19/18 (2014.01); H04N 19/186 (2014.01); H04N 19/96 (2014.01)
CPC H04N 19/132 (2014.11) [H04N 19/159 (2014.11); H04N 19/176 (2014.11); H04N 19/18 (2014.11); H04N 19/186 (2014.11); H04N 19/96 (2014.11)] 12 Claims
OG exemplary drawing
 
1. An image decoding apparatus, comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
obtain intra prediction mode information and residual information from a bitstream;
derive transform coefficients for a current block based on the residual information;
derive a first variable indicating whether a significant coefficient exists in a region excluding a DC component position of the current block, wherein a value of the first variable is initially set to 1, and, in response to a case where the significant coefficient exists in the region excluding the DC component position, the value of the first variable is modified to 0;
derive a second variable indicating whether the significant coefficient exists in a second region other than a first region at a top-left of the current block;
determine whether to obtain, from the bitstream, a low frequency non-separable transform (LFNST) index based on the first variable and the second variable, wherein, in response to the value of the first variable being equal to 0 and the second variable indicating that the significant coefficient does not exist in the second region, it is determined that the LFNST index is obtained from the bitstream, and wherein, in response to the value of the first variable being equal to 1 or the second variable indicating that the significant coefficient exists in the second region, it is determined that the LFNST index is not obtained from the bitstream;
obtain the LFNST index from the bitstream based on a result of the determination;
derive an intra prediction mode of a chroma block of the current block as a cross-component linear model (CCLM) mode based on the intra prediction mode information;
modify the intra prediction mode of the chroma block from the CCLM mode to an intra prediction mode of a luma block corresponding to the chroma block;
determine an LFNST set including LFNST matrices based on the modified intra prediction mode of the chroma block;
select one of the LFNST matrices based on the LFNST set and the LFNST index;
derive transform coefficients for the chroma block based on the selected LFNST matrix; and
derive residual samples for the chroma block based on the transform coefficients for the chroma block,
wherein the intra prediction mode of the chroma block is modified by using a specific position of the luma block corresponding to the chroma block, and
wherein the specific position is defined as a center position of the luma block.