Method and an apparatus for encoding/decoding residual coefficient

1. A method for decoding an image, comprising:

decoding, based on a predetermined scan order, a residual coefficient of a current block in the image from a bitstream;

performing inverse-quantization on the residual coefficient by using a quantization parameter; and

reconstructing a residual sample of the current block by performing inverse-transform on the inverse-quantized residual coefficient,

wherein the scan order is determined differently, based on encoding information related to the current block, as one of a plurality of scan order candidates pre-defined in a decoding apparatus,

wherein the encoding information includes a transform skip flag indicating whether the inverse-transform is skipped on the current block,

wherein the inverse-transform is adaptively performed on the inverse-quantized residual coefficient based on the transform skip flag,

wherein the plurality of the scan order candidates includes an up-right diagonal scan order and a bottom-left diagonal scan order.

2. The method of claim 1 ,

wherein the inverse-transform is performed based on a transform candidate set determined from among a plurality of transform candidate sets including a first transform candidate set and a second transform candidate set, and

wherein each of the transform candidate sets includes at least one transform type being available for the inverse-transform of the current block.

3. The method of claim 2 ,

wherein the transform candidate set of the current block is determined, based on a size of the current block, among the plurality of transform candidate sets.

4. The method of claim 3 ,

wherein, in response to the size of the current block being less than or equal to a threshold value, the first transform candidate set among the plurality of the transform candidate sets is determined as the transform candidate set, and

wherein, in response to the size of the current block being greater than the threshold value, the second transform candidate set among the plurality of the transform candidate sets is determined as the transform candidate set.

5. The method of claim 4 ,

wherein the threshold value is 32.

6. The method of claim 5 ,

wherein a number of transform types included in the first transform candidate set is different from a number of transform types included in the second transform candidate set.

7. The method of claim 6 ,

wherein the first transform candidate set includes DCT-VIII and DST-VII, and

wherein the second transform candidate set includes DCT-II, DCT-VIII, and DST-VII.

8. The method of claim 2 ,

wherein the transform candidate set of the current block is determined, based on first information signaled from the bitstream, among the plurality of transform candidate sets.

9. The method of claim 8 ,

wherein a number of transform types included in the first transform candidate set is equal to a number of transform types included in the second transform candidate set.

10. The method of claim 9 ,

wherein one of the transform types included in the first transform candidate set is different from the transform types included in the second transform candidate set, and

wherein another of the transform types included in the first transform candidate set is a same as one of the transform types included in the second transform candidate set.

11. The method of claim 10 ,

wherein the first transform candidate set includes DCT-II and DST-VII, and

wherein the second transform candidate set includes DCT-VIII and DST-VII.

12. The method of claim 11 ,

wherein a transform type for the inverse-transform of the current block is determined, from the determined transform candidate set, based on second information signaled from the bitstream.

13. A method for encoding an image, comprising:

obtaining a residual coefficient of a current block in the image by performing at least one of transform or quantization on a residual sample of the current block; and

encoding, based on a predetermined scan order, the residual coefficient of the current block,

wherein the transform is adaptively performed based on whether the transform is skipped on the current block,

wherein the quantization is performed based on a quantization parameter,

wherein the scan order is determined differently, based on whether the transform is skipped on the current block, as one of a plurality of scan order candidates pre-defined in an encoding apparatus,

wherein encoding information related to the current block is encoded into a bitstream,

wherein the encoding information includes a transform skip flag indicating whether the transform is skipped on the current block, and

wherein the plurality of the scan order candidates includes an up-right diagonal scan order and a bottom-left diagonal scan order.

14. A non-transitory computer-readable medium storing a bitstream generated by an encoding method, the method comprising:

obtaining a residual coefficient of a current block in an image by performing at least one of transform or quantization on a residual sample of the current block; and

encoding, based on a predetermined scan order, the residual coefficient of the current block,

wherein the transform is adaptively performed based on whether the transform is skipped on the current block,

wherein the quantization is performed based on a quantization parameter,

wherein the scan order is determined differently, based on whether the transform is skipped on the current block, as one of a plurality of scan order candidates pre-defined in an encoding apparatus,

wherein encoding information related to the current block is encoded into the bitstream, wherein the encoding information includes a transform skip flag indicating whether the transform is skipped on the current block,

wherein the plurality of the scan order candidates includes an up-right diagonal scan order and a bottom-left diagonal scan order.