Method of coding transform coefficient based on high frequency zeroing and apparatus thereof
An image decoding method performed by a decoding apparatus according to the present disclosure includes receiving a bitstream including residual information; deriving quantized transform coefficients for a current block based on the residual information included in the bitstream; deriving residual samples for the current block based on the quantized transform coefficients; and generating a reconstructed picture based on the residual samples for the current block.
1. An image decoding method performed by a decoding apparatus, comprising:
deriving transform coefficients for a current block based on residual information received from a bitstream;
deriving dequantized transform coefficients for the current block based on the transform coefficients;
deriving residual samples for the current block based on the dequantized transform coefficients; and
generating a reconstructed picture based on the residual samples for the current block,
wherein the current block includes a low frequency transform coefficient region including at least one non-zero transform coefficient and a region including only one or more zero transform coefficients other than the low frequency transform coefficient region,
wherein the residual information includes last significant coefficient prefix information and last significant coefficient suffix information on a position of a last non-zero transform coefficient among the transform coefficients for the current block,
wherein the last significant coefficient prefix information includes column position prefix information and row position prefix information,
wherein a maximum value of the column position prefix information is determined based on a width of the low frequency transform coefficient region,
wherein a maximum length of a first codeword for the column position prefix information is determined based on the width of the low frequency transform coefficient region,
wherein a maximum value of the row position prefix information is determined based on a height of the low frequency transform coefficient region, and
wherein a maximum length of a second codeword for the row position prefix information is determined based on the height of the low frequency transform coefficient region.
2. The image decoding method of claim 1 , wherein a size of the low frequency transform coefficient region is determined based on a width and height of the low frequency transform coefficient region.
3. The image decoding method of claim 2 , wherein the maximum length of the first codeword is determined based on the maximum value of the column position prefix information,
wherein the maximum length of the second codeword is determined based on the maximum value of the row position prefix information, and
wherein the first and second codewords are derived based on a truncated unary binarization.
4. The image decoding method of claim 3 , wherein the maximum length of the first codeword are determined to be 9 based on the width of the low frequency transform coefficient region being 32, and
wherein the maximum length of the second codeword are determined to be 9 based on the height of the low frequency transform coefficient region being 32.
5. The image decoding method of claim 3 , wherein a maximum binarized value of the first codeword is determined to be 111111111 based on a width of the current block being greater than 32 and the width of the low frequency transform coefficient region being 32, and
wherein a maximum binarized value of the second codeword is determined to be 111111111 based on a height of the current block being greater than 32 and the height of the low frequency transform coefficient region being 32.
6. The image decoding method of claim 3 , wherein the maximum length of the first codeword is determined based on cMax x , and
wherein the cMax x is calculated based on a following equation:
c Max x =(log 2(Min( W 1 ,W 2))<<1)−1
where the cMax x is equal to the maximum length of the first codeword, the W1 is a width of the current block, and the W2 is the width of the low frequency transform coefficient region.
7. The image decoding method of claim 3 , wherein the width of the low frequency transform coefficient region is 32,
wherein the maximum length of the first codeword is determined based on cMax x , and
wherein the cMax x is calculated based on a following equation:
c Max x =((Min(log 2 W 1,5))<<1)−1
where the cMax x is equal to the maximum length of the first codeword, and the W1 is a width of the current block.
8. The image decoding method of claim 3 , wherein the maximum length of the second codeword is determined based on cMax y , and
wherein the cMax y is calculated based on a following equation:
c Max y =(log 2(Min( H 1 ,H 2))<<1)−1
where the cMax y is equal to the maximum length of the second codeword, the H1 is a height of the current block, and the H2 is the height of the low frequency transform coefficient region.
9. The image decoding method of claim 3 , wherein the height of the low frequency transform coefficient is 32,
wherein the maximum length of the second codeword is determined based on cMax y , and
wherein the cMax y is calculated based on a following equation:
c Max y =((Min(log 2 H 1,5))<<1)−1
where the cMax y is equal to the maximum length of the second codeword, and the H1 is a height of the current block.
10. The image decoding method of claim 1 , wherein the current block is a square block or a non-square block,
wherein the width of the low frequency transform coefficient region is determined to be 32 based on a width of the current block being 64, and
wherein the height of the low frequency transform coefficient region is determined to be 32 based on a height of the current block being 64.
11. The image decoding method of claim 1 , wherein a size of the low frequency transform coefficient region is determined based on a size of the current block.
12. The image decoding method of claim 1 , wherein a size of the current block is 64×64, a size of the low frequency transform coefficient region is 32×32, and the maximum length of the first and second codeword is 9.
13. An image encoding method performed by an encoding apparatus, comprising:
deriving residual samples for a current block;
deriving transform coefficients for the current block based on the residual samples;
deriving quantized transform coefficients based on the transform coefficients for the current block; and
encoding residual information related to the quantized transform coefficients,
wherein the current block includes a low frequency transform coefficient region including at least one non-zero transform coefficient and a region including only one or more zero transform coefficients other than the low frequency transform coefficient region,
wherein the residual information includes last significant coefficient prefix information and last significant coefficient suffix information on a position of a last non-zero transform coefficient among the transform coefficients for the current block,
wherein the last significant coefficient prefix information includes column position prefix information and row position prefix information,
wherein a maximum value of the column position prefix information is determined based on a width of the low frequency transform coefficient region,
wherein a maximum length of a first codeword for the column position prefix information is determined based on the width of the low frequency transform coefficient region,
wherein a maximum value of the row position prefix information is determined based on a height of the low frequency transform coefficient region, and
wherein a maximum length of a second codeword for the row position prefix information is determined based on the height of the low frequency transform coefficient region.
14. A method of transmitting data for an image, comprising:
obtaining a bitstream for the image, wherein the bitstream is generated based on deriving residual samples for a current block, deriving transform coefficients for the current block based on the residual samples, deriving quantized transform coefficients based on the transform coefficients for the current block, and encoding residual information related to the quantized transform coefficients; and
transmitting the data including the bitstream,
wherein the current block includes a low frequency transform coefficient region including at least one non-zero transform coefficient and a region including only one or more zero transform coefficients other than the low frequency transform coefficient region,
wherein the residual information includes last significant coefficient prefix information and last significant coefficient suffix information on a position of a last non-zero transform coefficient among the transform coefficients for the current block,
wherein the last significant coefficient prefix information includes column position prefix information and row position prefix information,
wherein a maximum value of the column position prefix information is determined based on a width of the low frequency transform coefficient region,
wherein a maximum length of a first codeword for the column position prefix information is determined based on the width of the low frequency transform coefficient region,
wherein a maximum value of the row position prefix information is determined based on a height of the low frequency transform coefficient region, and
wherein a maximum length of a second codeword for the row position prefix information is determined based on the height of the low frequency transform coefficient region.