According to the present disclosure, a video decoding method performed by a video decoding device includes parsing remaining intra prediction mode information for a current block, deriving neighboring samples of the current block, deriving MPM list including MPM candidates of the current block, deriving an intra prediction mode of the current block based on the remaining intra prediction mode information, wherein the intra prediction mode is one of remaining intra prediction modes excluding the MPM candidates, deriving a prediction sample of the current block based on the intra prediction mode and the neighboring samples, and deriving a reconstructed picture based on the prediction sample, wherein the remaining intra prediction mode information is coded through a truncated binary (TB) binarization process, and wherein a binarization parameter for the TB binarization process is 60.