| CPC H04N 19/593 (2014.11) [H04N 19/122 (2014.11); H04N 19/176 (2014.11)] | 11 Claims |

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1. An image decoding apparatus, comprising:
a memory: and
at least one processor connected to the memory, the at least one processor configured to:
determine whether a non-separable transform is applied for a current block, based on a non-separable transform index obtained from a bitstream;
based on the non-separable transform being determined to be applied for the current block, determine a non-separable transform set index indicating a non-separable transform set for the current block from among four predetermined non-separable transform sets based on an intra prediction mode of the current block:
determine a transform kernel included in the non-separable transform set indicated by the non-separable transform set index as a non-separable transform matrix for the current block; and
perform secondary inverse transform for the current block based on the non-separable transform matrix,
wherein the non-separable transform matrix is applied for R coefficients included in the current block having a square shape to generate N transformed coefficients, R being smaller than N, N being equal to a total number of coefficients for which the non-separable transform matrix is applied in the current block.
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