Residual coding method and device for same

1. An image decoding method performed by a decoding apparatus, the method comprising:

obtaining residual information from a bitstream;

deriving a quantized transform coefficient for a current block based on the residual information;

deriving a transform coefficient based on the quantized transform coefficient;

deriving a residual sample for the current block based on the transform coefficient; and

generating a reconstructed picture based on the residual sample for the current block,

wherein the residual information includes a significant coefficient flag representing whether a 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 about whether the transform coefficient level is larger than a first reference value, a second transform coefficient level flag about whether the transform coefficient level is larger than a second reference value and remainder information of the transform coefficient level,

wherein deriving the quantized transform coefficients comprises:

deriving the quantized transform coefficient based on decoding the parity level flag and decoding the first transform coefficient level flag, and

wherein the decoding of the first transform coefficient level flag is performed prior to the decoding of the parity level flag.

2. The method of claim 1 , wherein the sum of the number of significant coefficient flags for the quantized transform coefficients within the current block, the number of parity level flags, the number of first transform coefficient level flags and the number of second transform coefficient level flags, which are comprised in the residual information, is a predetermined threshold or less.

3. The method of claim 2 , wherein the predetermined threshold is determined based on the size of the current block.

4. The method of claim 1 , wherein an initialization process is performed to derive at least one rice parameter for a current sub-block comprised in the current block.

5. The method of claim 4 , wherein the rice parameter for a current transform coefficient within the current sub-block is derived based on a last rice parameter for a transform coefficient of a previous order of the current transform coefficient, and

wherein if the current transform coefficient is the first transform coefficient of the current sub-block, a value of the last rice parameter for the transform coefficient of the previous order is zero.

6. The method of claim 4 , wherein the size of the current sub-block is 2×2 or 4×4.

7. The method of claim 5 , wherein the rice parameter for the current transform coefficient is derived based on neighboring reference transform coefficients of the current transform coefficient, and the number of neighboring reference transform coefficients is 4 or less.

8. The method of claim 7 , wherein a temporary sum coefficient is derived based on the neighboring reference transform coefficients, and

wherein the value of the rice parameter is determined as zero if the value of the temporary sum coefficient is smaller than a first threshold, the value of the rice parameter is determined as 1 if the value of the temporary sum coefficient is the first threshold or more and smaller than a second threshold, the value of the rice parameter is determined as 2 if the value of the temporary sum coefficient is the second threshold or more and smaller than a third threshold, and the value of the rice parameter is determined as 3 if the value of the temporary sum coefficient is the third threshold or more.

9. The method of claim 8 , wherein the first threshold is 1, 2, or 3, the second threshold is 4, 5, or 6, and the third threshold is 10, 11, or 12.

10. An image encoding method performed by an encoding apparatus, the method comprising:

deriving a residual sample for a current block;

deriving a transform coefficient for the current block based on the residual sample;

deriving a quantized transform coefficient based on the transform coefficient; and

encoding residual information comprising information related to the quantized transform coefficient,

wherein the residual information includes a significant coefficient flag representing whether a 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 about whether the transform coefficient level is larger than a first reference value, a second transform coefficient level flag about whether the transform coefficient level is larger than a second reference value and remainder information of the transform coefficient level,

wherein the encoding of the residual information comprises:

encoding the parity level flag and encoding the first transform coefficient level flag, and

wherein the encoding of the first transform coefficient level flag is performed prior to the encoding of the parity level flag.

11. A transmission method of data for an image, the method comprising:

obtaining a bitstream for the image, wherein the bitstream is generated based on deriving a residual sample for a current block, deriving a transform coefficient for the current block based on the residual sample, deriving a quantized transform coefficients based on the transform coefficient, and encoding residual information comprising information related to the quantized transform coefficient; and

transmitting the data comprising the bitstream,

wherein the residual information includes a significant coefficient flag representing whether a 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 about whether the transform coefficient level is larger than a first reference value, a second transform coefficient level flag about whether the transform coefficient level is larger than a second reference value and remainder information of the transform coefficient level,

wherein the encoding of the residual information comprises:

encoding the parity level flag and encoding the first transform coefficient level flag, and

wherein the encoding of the first transform coefficient level flag is performed prior to the encoding of the parity level flag.