| CPC H04N 19/60 (2014.11) [H04N 19/122 (2014.11); H04N 19/124 (2014.11); H04N 19/132 (2014.11); H04N 19/176 (2014.11); H04N 19/18 (2014.11); H04N 19/70 (2014.11)] | 8 Claims |
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1. An image decoding method performed by a decoding apparatus, comprising:
obtaining residual information from a bitstream;
deriving transform coefficients for a current block based on the residual information;
determining whether a Low Frequency Non-Separable Transform (LFNST) index is parsed;
parsing the LFNST index based on the determination that the LFNST index is parsed;
deriving modified transform coefficients by applying an LFNST matrix derived based on the LFNST index to the transform coefficients in a first region at a top-left of the current block;
deriving residual samples for the current block based on an inverse primary transform for the modified transform coefficients; and
generating a reconstructed picture based on the residual samples for the current block,
wherein determining whether the LFNST index is parsed comprising:
deriving a first variable related to whether a significant coefficient exists in a region excluding a Direct-Current (DC) region of the current block; and
deriving a second variable related to whether the significant coefficient exists in a second region other than the first region in the current block;
wherein the first variable is derived as 0 based on an index of a subblock including a last significant coefficient in the current block being 0 and a position of the last significant coefficient in the subblock being greater than 0, and
wherein the LFNST index is parsed based on the first variable being 0 and the second variable being related to that the significant coefficient does not exist in the second region.
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