Method and apparatus for processing video signal

1. A method of decoding a video signal, the method comprising:

determining whether at least one non-zero residual coefficient is included in a current transform block;

decoding residual coefficients of the current transform block according to a scanning order;

performing an inverse-quantization for the current transform block;

determining whether an inverse-transform is skipped for the current transform block or not; and

obtaining residual samples of the current transform block by performing or skipping the inverse-transform for the current transform block,

wherein in response to a determination that the inverse-transform is not skipped for the current transform block, obtaining the residual samples of the current transform block comprises:

performing a first inverse-transform on inverse-quantized residual coefficients resultant from the inverse-quantization; and

performing a second inverse-transform on first inverse-transformed residual coefficients resultant from the first inverse-transform,

wherein residual coefficients each of which the scanning order is earlier than a residual coefficient at a position pre-defined in a decoding apparatus, are equal to 0 and information on the residual coefficients each of which the scanning order is earlier than the residual coefficient at the position pre-defined in the decoding apparatus is not signaled via a bitstream,

wherein whether a transform skip flag of the current transform block is present in the 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 in 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 in the vertical direction, the transform skip flag for the current transform block is not present in the bitstream, and skipping the inverse-transform is not allowed for the current transform block.

2. The method of claim 1 , wherein the scanning order of the current transform block is determined by a diagonal scanning order or an inverse-diagonal scanning order.

3. The method of claim 1 , wherein a first absolute value flag indicating whether an absolute value of a residual coefficient is greater than 1 is decoded from the bitstream,

wherein when the first absolute value flag indicates that the absolute value of the residual coefficient is greater than 1, a parity flag indicating whether the absolute value is an even number or an odd number and a second absolute value flag indicating whether the absolute value of the residual coefficient is greater than 3 are further decoded from the bitstream, and

wherein when the second absolute value flag indicates that the absolute value of the residual coefficient is not greater than 3, the absolute value of the residual coefficient is determined, based on the parity flag, as either 2 or 3.

4. 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 according to a scanning order,

wherein obtaining the transform coefficients of the current transform block comprises:

performing a first transform on the residual samples; and

performing a second transform on first transformed residual samples resultant from the first transform,

wherein transform coefficients each of which the scanning order is earlier than a transform coefficient at a position pre-defined in an encoding apparatus, are forcibly changed to 0 and information on the residual coefficients corresponding to the transform coefficients is not encoded into a bitstream,

wherein whether a transform skip flag of the current transform block is explicitly encoded into the 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 in 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 in the vertical direction, the transform skip flag for the current transform block is not encoded into the bitstream, and skipping the transform is not allowed for the current transform block.

5. The method of claim 4 , wherein the scanning order of the current transform block is determined by a diagonal scanning order or an inverse-diagonal scanning order.

6. The method of claim 4 , wherein a first absolute value flag indicating whether an absolute value of a residual coefficient is greater than 1 is encoded into the bitstream, and

wherein when the absolute value of the residual coefficient is greater than 1, a parity flag indicating whether the absolute value is an even number or an odd number and a second absolute value flag indicating whether the absolute value of the residual coefficient is greater than 3 are further encoded into the bitstream.

7. The method of claim 1 , wherein the current transform block is divided into a plurality of sub blocks,

wherein the residual coefficients of the current transform block are decoded in units of sub-blocks,

wherein in response to the current transform block with at least one of a width or a height less than 4, the current transform block is divided into the sub-blocks with a size of 2×8 or 8×2, and

wherein in response to the current transform block with the width and the height greater than or equal to 4, the current transform block is divided into the sub-blocks with a size of 4×4.

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

a coded block flag for determining whether there exist at least one non-zero residual coefficients 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 in response to a determination that the inverse-transform is not skipped for the current transform block, the residual samples are derived by performing a first inverse-transform on the inverse-quantized residual coefficients, and performing a second inverse-transform on first inverse-transformed residual coefficients resultant from the first inverse-transform,

wherein residual coefficients, each of which a scanning order is earlier than a residual coefficient at a pre-defined position, are equal to 0 and information on the residual coefficients each of which the scanning order is earlier than the residual coefficient at the pre-defined position is not included in the compressed video data,

wherein whether a transform skip flag 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 in 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 in the vertical direction, the transform skip flag for the current transform block is not present in the compressed video data, and skipping the inverse-transform is not allowed for the current transform block.