Method and apparatus for processing video signal by skipping inverse-transform

A method of encoding a video signal, the method comprising:

• obtaining residual samples of a current transform block;
• obtaining transform coefficients of the current transform block;
• obtaining residual coefficients by performing a quantization on the transform coefficients;
• encoding a coded block flag indicating whether at least one non-zero residual coefficient is included in the current transform block;
• and
• encoding the residual coefficients of the current transform block,
• wherein the residual coefficients in the current transform block are encoded in a unit of a sub-block,
• wherein a size of the sub-block is determined based on whether at least one of a width or a height of the current transform block is less than 4,
• wherein in response that at least one of the width or the height of the current transform block is less than 4, the size of the sub-block is determined as 2×2, 2×8, or 8×2,
• wherein in response that both the width and the height of the current block are equal to or greater than 4, the size of the sub-block is determined as 4×4,
• wherein whether to encode a transform skip flag, indicating whether the transform is skipped or not, of the current transform block into a bitstream or not is determined based on whether a coding block, including the current transform block, is partitioned into a plurality of transform blocks in a horizontal direction or a vertical direction, and
• wherein in response that the current transform block is one of the plurality of transform blocks generated by partitioning the coding block in the horizontal direction or the vertical direction, encoding the transform skip flag of the current transform block is omitted, and the transform is not skipped for the current transform block.

A non-transitory computer-readable medium for storing compressed video data, the compressed video data comprising:

• a coded block flag for determining whether there exist at least one non-zero residual coefficient in a current transform block;
• and
• information on residual coefficients of the current transform block,
• wherein inverse-quantized residual coefficients of the current transform block are obtained by performing an inverse-quantization for the current transform block,
• wherein residual samples of the current transform block are obtained by skipping or performing an inverse-transform for the current transform block,
• wherein the residual coefficients in the current transform block are decoded in a unit of a sub-block,
• wherein a size of the sub-block is determined based on whether at least one of a width or a height of the current transform block is less than 4,
• wherein in response that at least one of the width or the height of the current transform block is less than 4, the size of the sub-block is determined as 2×2, 2×8, or 8×2, and
• wherein in response that both the width and the height of the current block are equal to or greater than 4, the size of the sub-block is determined as 4×4,
• wherein whether a transform skip flag, indicating whether the inverse-transform is skipped or not, of the current transform block is present in the compressed video data or not is determined based on whether a coding block, including the current transform block, is partitioned into a plurality of transform blocks in a horizontal direction or a vertical direction, and
• wherein in response that the current transform block is one of the plurality of transform blocks generated by partitioning the coding block in the horizontal direction or the vertical direction, the transform skip flag of the current transform block is not present in the compressed video data, and skipping the inverse-transform for the current transform block is not allowed.