Transform coefficient coding method and device
An image decoding method according to the present document comprises the steps of: receiving a bitstream including residual information; deriving a quantized transform coefficient for a current block on the basis of the residual information included in the bitstream; deriving a residual sample for the current block on the basis of the quantized transform coefficient; and generating a restoration picture on the basis of the residual sample for the current block, wherein the residual information includes position information for indicating the position of a transform coefficient, which is not the last 0 in a transform block, and the position information can be derived if a transform skip is not applied to the transform block.
1. An image decoding apparatus comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
receive a bitstream including residual information;
derive a quantized transform coefficient for a current block based on the residual information included in the bitstream;
derive a residual sample for the current block based on the quantized transform coefficient; and
generate a reconstructed picture based on the residual sample for the current block,
wherein the residual information includes position information related to the position of a last non-zero transform coefficient in a transform block,
wherein the position information is parsed based on a value of a transform skip flag related to whether a transform skip is applied to the transform block being equal to 0 and a size of the transform block being equal to or more than a certain value, and
wherein the parsing of the position information is skipped based on the value of the transform skip flag being equal to 1.
2. The image decoding apparatus of claim 1 , wherein the position information includes information related to a prefix of the column position of the last significant coefficient in the scanning order in the transform block, and information related to a prefix of the row position of the last significant coefficient in the scanning order in the transform block, and information related to a suffix of the column position of the last significant coefficient in the scanning order in the transform block, and information related to a suffix of the row position of the last significant coefficient in the scanning order in the transform block.
3. The image decoding apparatus of claim 1 , wherein the residual information includes a significant coefficient flag related to whether or not the quantized transform coefficient is a non-zero significant coefficient, a parity level flag for a parity of a transform coefficient level for the quantized transform coefficient, a first transform coefficient level flag related to whether or not the transform coefficient level is greater than a first threshold value, and a second transform coefficient level flag related to whether or not the transform coefficient level for the quantized transform coefficient is greater than a second threshold value, and
wherein the at least one processor, to derive the quantized transform coefficient, further configured to:
decode the first transform coefficient level flag and the parity level flag; and
derive the quantized transform coefficient based on a value of the decoded parity level flag and a value of the decoded first transform coefficient level flag,
wherein the decoding of the first transform coefficient level flag is performed prior to the decoding of the parity level flag.
4. An image encoding apparatus comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
derive a residual sample for a current block;
derive a quantized transform coefficient based on the residual sample for the current block; and
encode residual information including information on the quantized transform coefficient,
wherein the residual information includes position information related to the position of a last non-zero transform coefficient in a transform block,
wherein the position information is encoded based on a value of a transform skip flag related to whether a transform skip is applied to the transform block being equal to 0 and a size of the transform block being equal to or more than a certain value, and
wherein encoding of the position information is skipped based on the value of the transform skip flag being equal to 1.
5. The image encoding apparatus of claim 4 , wherein the position information includes information related to a prefix of the column position of the last significant coefficient in the scanning order in the transform block, and information related to a prefix of the row position of the last significant coefficient in the scanning order in the transform block, and information related to a suffix of the column position of the last significant coefficient in the scanning order in the transform block, and information related to a suffix of the row position of the last significant coefficient in the scanning order in the transform block.
6. The image encoding apparatus of claim 4 , wherein the residual information includes a significant coefficient flag related to whether or not the quantized transform coefficient is a non-zero significant coefficient, a parity level flag for a parity of a transform coefficient level for the quantized transform coefficient, a first transform coefficient level flag related to whether or not the transform coefficient level is greater than a first threshold value, and a second transform coefficient level flag related to whether or not the transform coefficient level for the quantized transform coefficient is greater than a second threshold value, and
wherein the at least one processor, to derive the quantized transform coefficient, further configured to:
encode the first transform coefficient level flag and the parity level flag; and
derive the quantized transform coefficient based on a value of the encoded parity level flag and a value of the encoded first transform coefficient level flag,
wherein the encoding of the first transform coefficient level flag is performed prior to the encoding of the parity level flag.
7. An apparatus for transmitting a bitstream for an image, the apparatus comprising:
at least one processor configured to obtain the bitstream generated by an encoding apparatus; and
a transmitter configured to transmit the bitstream, the bitstream is generated by:
deriving a residual sample for a current block;
deriving a quantized transform coefficient based on the residual sample for the current block; and
encoding residual information including information on the quantized transform coefficient,
wherein the residual information includes position information related to the position of a last non-zero transform coefficient in a transform block,
wherein the position information is encoded based on a value of a transform skip flag related to whether a transform skip is applied to the transform block being equal to 0 and a size of the transform block being equal to or more than a certain value, and
wherein encoding of the position information is skipped based on the value of the transform skip flag being equal to 1.