Method of determining transform coefficient scan order based on high frequency zeroing and apparatus thereof

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

receiving a bitstream including residual information;

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

deriving residual samples for the current block from the transform coefficients based on an inverse transform; and

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

wherein the residual information includes a last_sig_coeff_x_prefix syntax element related to an x component of a position of a last significant coefficient of the current block,

wherein based on a width of the current block being equal to 64,

and high frequency zeroing being applied to the current block such that the current block includes a high frequency zeroing out region and a low frequency transform coefficient region, the low frequency transform coefficient region including at least one significant transform coefficient and the high frequency zeroing out region is a region outside of the low frequency transform coefficient region in the current block, a maximum length of a codeword for the last_sig_coeff_x_prefix syntax element is determined as 9 for a width of a block being equal to 64 based on a determination that a width of the low frequency coefficient region is set to 32, and

wherein the last_sig_coeff_x_prefix syntax element is based on truncated rice binarization based on the width of the low frequency transform coefficient region being 32.

2. The image decoding method of claim 1 , wherein the residual information includes coded subblock flag representing whether all transform coefficient levels of transform coefficients for a subblock in the current block are equal to 0, and

the coded subblock flag is for the subblock located in the low frequency transform coefficient region.

3. The image decoding method of claim 1 , wherein transform coefficient subblock scanning is applied to subblocks located in the low frequency transform coefficient region.

4. The image decoding method of claim 1 , wherein based on the current block of which width is 64,

for x component of the position of the last significant coefficient with a value of one of 24 through 31, the codeword for the last_sig_coeff_x_prefix syntax element is “111111111”.

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

deriving residual samples for a current block;

deriving transform coefficients for the current block based on the residual samples for the current block;

encoding residual information related with the transform coefficients,

wherein the residual information includes a last sig coeff x prefix syntax element related to an x component of a position of a last significant coefficient of the current block,

wherein based on a width of the current block being equal to 64 ,

and high frequency zeroing being applied to the current block such that the current block includes a high frequency zeroing out region and a low frequency transform coefficient region, the low frequency transform coefficient region including at least one significant transform coefficient and the high frequency zeroing out region is a region outside of the low frequency transform coefficient region in the current block, a maximum length of a codeword for the last_sig_coeff_x_prefix syntax element is determined as 9 for a width of a block being equal to 64 based on a determination that a width of the low frequency coefficient region is set to 32, and

wherein the last_sig_coeff_x_prefix syntax element is based on truncated rice binarization based on the width of the low frequency transform coefficient region being 32.

6. The image encoding method of claim 5 , wherein the residual information includes coded subblock flag representing whether all transform coefficient levels of transform coefficients for a subblock in the current block are equal to 0, and

the coded subblock flag is for the subblock located in the low frequency transform coefficient region.

7. The image encoding method of claim 5 , wherein transform coefficient subblock scanning is applied to subblocks located in the lowfrequency transform coefficient region.

8. The image encoding method of claim 5 , wherein based on the current block of which width is 64,

for x component of the position of the last significant coefficient with a value of one of 24 through 31, the codeword for the last_sig_coeff_x_prefix syntax element is “111111111”.

9. A non-transitory computer readable storage medium storing a bitstream of image information generated by a method, the method comprising:

deriving residual samples for a current block;

deriving transform coefficients for a current block based on the residual samples for the current block; and

encoding the image information including residual information related with the transform coefficients to output the bitstream,

wherein the residual information includes a last_sig_coeff_x_prefix syntax element related to an x component of a position of a last significant coefficient of the current block,

wherein based on a width of the current block being equal to 64,

and high frequency zeroing being applied to the current block such that the current block includes a high frequency zeroing out region and a low frequency transform coefficient region, the low frequency transform coefficient region including at least one significant transform coefficient and the high frequency zeroing out region is a region outside of the low frequency transform coefficient region in the current block, a maximum length of a codeword for the last_sig_coeff_x_prefix syntax element is determined as 9 for a width of a block being equal to 64 based on a determination that a width of the low frequency coefficient region is set to 32, and

wherein the last_sig_coeff_x_prefix syntax element is based on truncated rice binarization based on the width of the low frequency transform coefficient region being 32.

10. The non-transitory computer readable storage medium of claim 9 , wherein based on the current block of which width is 64,

for x component of the position of the last significant coefficient with a value of one of 24 through 31, the codeword for the last_sig_coeff_x_prefix syntax element is “111111111”.