obtaining residual information from a bitstream;

deriving transform coefficients for the current block based on the residual information; deriving modified transform coefficients based on a low-frequency non-separable transform (LFNST) for the transform coefficients;

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 deriving transform coefficients comprises,

determining whether a last significant coefficient is present at (0, 0) of the current block; and

determining whether a significant coefficient is present in a second region other than a first region at a top-left of the current block,

wherein the LFNST is performed based on parsing an LFNST index,

wherein LFNST index is parsed from the bitstream when it is determined that the position of the last significant coefficient in the subblock having the index 0 is greater than 0 and the significant coefficient does not exist in the second region, and

wherein based on a width and a height of the current block being 4 or more and the width or the height of the current block being less than 8, the first region is a 4×4 area at the top-left of the current block, and based on the significant coefficient being present in the second region other than the 4×4 area at the top-left, the LFNST index is not parsed.