A method for decoding a video comprising obtaining transformed coefficients of a block from a bitstream, generating inverse-quantized transformed coefficients by performing inverse-quantization and a first clipping on the transformed coefficients, generating sample values by performing vertical inverse-transformation and a second clipping on the inverse-quantized transformed coefficients; and generating residual values by performing horizontal inverse-transformation on the sample values, wherein the first clipping is performed for restricting the inverse-quantized transformed coefficients to a range of a first bitdepth, the second clipping is performed for restricting the sample values to a range of a second bitdepth.