Adaptive loop filter-based video or image coding

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

obtaining image information including information related to whether an adaptive loop filter (ALF) is applied, coefficient information for the ALF, information related to whether fixed filter set is applied, and residual information from a bitstream, wherein the coefficient information is included in the image information based on the information related to whether the ALF is applied;

generating reconstructed samples based on the residual information;

deriving filter coefficients for the ALF based on the coefficient information; and

generating modified reconstructed samples based on the reconstructed samples and the filter coefficients,

wherein the coefficient information is obtained by decoding based on Exponential-Golomb coding,

wherein the Exponential-Golomb coding is based on a fixed order,

wherein the image information further includes information on a fixed filter index indicating one of the fixed filters for the ALF based on the information related to whether the fixed filter set is applied,

wherein the filter coefficients are derived based on the information on the fixed filter index,

wherein the information on the fixed filter index is obtained based on a binarization process, and

wherein the binarization process is performed based on a truncated binary (TB) binarization.

2. The method of claim 1 , wherein the fixed order is pre-determined without signaling information on the fixed order.

3. The method of claim 2 , wherein the fixed order is one of 0, 2, or 3.

4. The method of claim 2 , wherein the fixed order is 0 or 2 based on the reconstructed samples being luma samples.

5. The method of claim 2 , wherein the fixed order is 0 or 3 based on the reconstructed samples being chroma reconstructed samples.

6. The method of claim 2 , wherein the fixed order is determined based on positions of the filter coefficients in a filter shape for the ALF.

7. The method of claim 6 , wherein the fixed order is determined based on the following table,

C 0

2

C 1

2

C 2

2

C 3

2

C 4

2

C 5

3

C 6

3

C 7

3

C 8

2

C 9

2

C 10

2

C 11

3

wherein, in the table, C0 to C11 represent filter coefficients depending on positions within the filter shape, and 2 or 3 represents a fixed order corresponding to each filter coefficient.

8. The method of claim 1 , wherein a bin string of the information on the fixed filter index includes 5 bins,

wherein each of the five bins is bypass-based decoded.

9. The method of claim 1 , wherein the image information includes information on an ALF clipping,

wherein the information on the ALF clipping is decoded and obtained based on the Exponential-Golomb coding using the fixed order.

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

deriving prediction samples of a current block in a current picture;

deriving residual samples based on the prediction samples;

generating residual information based on the residual samples;

generating reconstructed samples based on the residual samples;

determining whether an adaptive loop filter (ALF) is applied;

determining whether fixed filter set is applied;

deriving filter coefficients for the ALF for the reconstructed samples;

generating coefficient information for the ALF based on the filter coefficients; and

encoding image information including information related to whether the ALF is applied, the coefficient information, information related to whether the fixed filter set is applied and the residual information,

wherein the coefficient information is encoded based on Exponential-Golomb coding,

wherein the Exponential-Golomb coding is based on a fixed order,

wherein the image information further includes information on a fixed filter index indicating one of the fixed filters for the ALF based on the fixed filter set being applied,

wherein the filter coefficients are derived based on the information on the fixed filter index,

wherein the information on the fixed filter index is obtained based on a binarization process, and

wherein the binarization process is performed based on a truncated binary (TB) binarization.

11. The method of claim 10 , wherein the fixed order is one of 0, 2, or 3.

12. The method of claim 11 , wherein the fixed order is 0 or 2 based on the reconstructed samples being luma samples.

13. The method of claim 11 , wherein the fixed order is 0 or 3 based on the reconstructed samples being chroma reconstructed samples.

14. A non-transitory computer-readable digital storage medium,

storing a bitstream generated by a method, the method comprising:

deriving prediction samples of a current block in a current picture;

deriving residual samples based on the prediction samples;

generating residual information based on the residual samples;

generating reconstructed samples based on the residual samples;

determining whether an adaptive loop filter (ALF) is applied;

determining whether fixed filter set is applied;

deriving filter coefficients for the ALF for the reconstructed samples;

generating coefficient information for the ALF based on the filter coefficients; and

generating the bitstream by encoding image information including information related to whether the ALF is applied, the coefficient information and the residual information,

wherein the coefficient information is encoded based on Exponential-Golomb coding,

wherein the Exponential-Golomb coding is based on a fixed order,

wherein the image information further includes information on a fixed filter index indicating one of the fixed filters for the ALF based on the fixed filter set being applied,

wherein the filter coefficients are derived based on the information on the fixed filter index,

wherein the information on the fixed filter index is obtained based on a binarization process, and

wherein the binarization process is performed based on a truncated binary (TB) binarization.