Image decoding method using residual information in image coding system, and device for same
An image decoding method performed by a decoding device, according to the present document, comprises the steps of: receiving a bitstream including residual information of a current block; deriving a specific number of context-encoding bins for context syntax elements for a current sub-block of the current block; decoding the context syntax elements for the current sub-block included in the residual information on the basis of the specific number; deriving transform coefficients for the current sub-block on the basis of the decoded context syntax elements; deriving residual samples for the current block on the basis of the transform coefficients; and generating a reconstructed picture on the basis of the residual samples.
1. A decoding apparatus for image decoding, the decoding apparatus comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
obtain a transform skip flag of a current block from a bitstream;
obtain residual information of the current block from the bitstream based on the transform skip flag, wherein the residual information is residual information on transform skip;
derive a specific number of context-coded bins for context syntax elements for a current sub-block of the current block;
decode the context syntax elements for the current sub-block included in the residual information based on the specific number;
derive transform coefficients for the current sub-block based on the decoded context syntax elements;
derive residual samples for the current block based on the transform coefficients; and
generate a reconstructed picture based on the residual samples,
wherein when a number of context coded bins for context syntax elements of transform coefficients derived before a specific transform coefficient of the current sub-block reaches the specific number, a bypass syntax element for the specific transform coefficient included in the residual information is decoded,
wherein whether the number of the context-coded bins reaches the specific number is determined by the sum of the number of the context coded bins for the context syntax elements of the transform coefficients derived before the specific transform coefficient.
2. The decoding apparatus of claim 1 ,
wherein when the number of the context coded bins reaches the specific number, decoding of context syntax elements for the specific transform coefficient is omitted, and
wherein a value of the specific transform coefficient is derived based on the bypass syntax element for the specific transform coefficient.
3. The decoding apparatus of claim 1 , wherein the context syntax elements include a significant coefficient flag indicating whether a transform coefficient is a non-zero transform coefficient, a parity level flag for a parity of a transform coefficient level for the transform coefficient, a first transform coefficient level flag for whether the transform coefficient level is greater than a first threshold, and a second transform coefficient level flag for whether the transform coefficient level of the transform coefficient is greater than a second threshold.
4. The decoding apparatus of claim 1 , wherein the context syntax elements include an significant coefficient flag indicating whether a transform coefficient is a non-zero transform coefficient, a sign flag indicating a sign of the transform coefficient, a first transform coefficient level flag for whether a transform coefficient level for the transform coefficient is greater than a first threshold, and a parity level flag for a parity of the transform coefficient level.
5. The decoding apparatus of claim 1 , wherein the specific number is set based on a size of the current block.
6. The decoding apparatus of claim 1 , wherein it is not determined whether the number of the context-coded bins reaches the specific number in a decoding process of each of the context syntax elements.
7. An encoding apparatus for image encoding, the encoding apparatus comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
derive residual samples for a current block;
derive a transform skip flag for whether transform is applied to the current block;
derive transform coefficients in a current sub-block of the current block based on the residual samples;
derive a specific number of context-coded bins for context syntax elements for the current sub-block;
encode the context syntax elements based on the specific number; and
generate a bitstream including the transform skip flag and residual information for the current block including the encoded context syntax elements, wherein the residual information is residual information on transform skip,
wherein when a number of context coded bins for context syntax elements of transform coefficients derived before a specific transform coefficient of the current sub-block reaches the specific number, a bypass syntax element for the specific transform coefficient included in the residual information is encoded,
wherein whether the number of the context-coded bins reaches the specific number is determined by the sum of the number of the context coded bins for the context syntax elements of the transform coefficients derived before the specific transform coefficient.
8. The encoding apparatus of claim 7 , wherein the context syntax elements include an significant coefficient flag indicating whether a transform coefficient is a non-zero transform coefficient, a parity level flag for a parity of a transform coefficient level for the transform coefficient, a first transform coefficient level flag regarding whether the transform coefficient level is greater than a first threshold, and a second transform coefficient level flag regarding whether the transform coefficient level of the transform coefficient is greater than a second threshold.
9. The encoding apparatus of claim 7 ,
wherein when the number of the context coded bins reaches the specific number, encoding of context syntax elements for the specific transform coefficient is omitted, and
wherein a value of the specific transform coefficient is derived based on the bypass syntax element for the specific transform coefficient.
10. The encoding apparatus of claim 7 ,
wherein it is not determined whether the number of the context-coded bins reaches the specific number in an encoding process of each of the context syntax elements.
11. The encoding apparatus of claim 7 , wherein the specific number is set based on a size of the current block.
12. A transmitting apparatus of data for an image, comprising:
at least one processor configured to obtain a bitstream for the image,
wherein the bitstream is generated based on deriving residual samples for a current block, deriving a transform skip flag for whether transform is applied to the current block, deriving transform coefficients in a current sub-block of the current block based on the residual samples, deriving a specific number of context-coded bins for context syntax elements for the current sub-block, encoding the context syntax elements based on the specific number, and generating the video data including the transform skip flag and residual information for the current block including the encoded context syntax elements, wherein the residual information is residual information on transform skip; and
a transmitter configured to transmit the data comprising the bitstream,
wherein when a number of context coded bins for context syntax elements of transform coefficients derived before a specific transform coefficient of the current sub-block reaches the specific number, a bypass syntax element for the specific transform coefficient included in the residual information is encoded,
wherein whether the number of the context-coded bins reaches the specific number is determined by the sum of the number of the context coded bins for the context syntax elements of the transform coefficients derived before the specific transform coefficient.
13. The transmitting apparatus of claim 12 ,
wherein it is not determined whether the number of the context-coded bins reaches the specific number in an encoding process of each of the context syntax elements.