| CPC H04N 19/18 (2014.11) [H04N 19/11 (2014.11); H04N 19/122 (2014.11); H04N 19/124 (2014.11); H04N 19/129 (2014.11); H04N 19/159 (2014.11); H04N 19/176 (2014.11); H04N 19/184 (2014.11); H04N 19/593 (2014.11); H04N 19/61 (2014.11); H04N 19/91 (2014.11)] | 8 Claims |
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1. An image decoding method performed by a decoding apparatus, comprising:
deriving secondary transform coefficients for a target block from residual information;
deriving primary transform coefficients based on an inverse non-separable secondary transform of primary transform coefficients, wherein the inverse non-separable secondary transform derives the primary transform coefficients through a matrix operation of the secondary transform coefficients and a transform kernel matrix, a number of the primary transform coefficients is greater than a number of the secondary transform coefficients, the secondary transform coefficients are derived from the a top-left 4×4 area of the target block;
deriving residual samples for the target block based on an inverse primary transform for the primary transform coefficients; and
generating a reconstructed picture based on the residual samples for the target block and prediction samples derived based on an intra prediction mode for the target block,
wherein the inverse non-separable secondary transform is performed based on the transform kernel matrix selected from a transform set including a plurality of transform kernel matrices,
wherein the transform set is determined according to a mapping relationship based on the intra prediction mode applied to the target block,
wherein five or more intra prediction modes are mapped to one non-separable secondary transform set, and
wherein the five or more intra prediction modes are directional modes.
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