Image encoding method and device, and image decoding method and device

1. An image decoding method comprising:

obtaining a plurality of largest coding units by splitting a current image based on a size information of a largest coding unit;

obtaining one or more coding units comprising a current coding unit, by hierarchically splitting at least one largest coding unit among the plurality of largest coding units, based on a split shape mode;

based on a prediction mode of the current coding unit being an inter mode, obtaining, from a bitstream, a first coded block flag indicating whether the current coding unit comprises one or more non-zero significant transform coefficients;

based on the first coded block flag indicating that the current coding unit comprises one or more non-zero significant transform coefficients, identifying whether at least one of a height and a width of the current coding unit is greater than a predetermined size;

based on whether the at least one of the height and the width of the current coding unit is greater than the predetermined size, obtaining at least one transform unit included in the current coding unit;

based on the at least one of the height and the width of the current coding unit being greater than the predetermined size, obtaining a second coded block flag from the bitstream, the second coded block flag indicating whether a block of a luma component included in the at least one transform unit comprises one or more non-zero significant transform coefficients;

based on the height and the width of the current coding unit being less than or equal to the predetermined size, identifying that the second coded block flag indicates that the block of the luma component included in the at least one transform unit comprises one or more non-zero significant transform coefficients;

obtaining a residual signal of the block of the luma component included in the at least one transform unit, based on the second coded block flag;

reconstructing the current coding unit based on the residual signal; and

reconstructing the current image comprising the current coding unit, based on the reconstructed current coding unit,

wherein the split shape mode indicates at least one of whether to perform splitting, a split direction, or a split type, and

wherein the split type corresponds to one of binary splitting, tri splitting, and quad splitting.

2. The image decoding method of claim 1 , wherein the obtaining of the first coded block flag from the bitstream comprises,

based on the prediction mode of the current coding unit being the inter mode and being neither a merge mode nor a skip mode, obtaining, from the bitstream, the first coded block flag indicating whether blocks of the luma component and chroma components included in the current coding unit comprise one or more non-zero significant transform coefficients, and

based on the prediction mode of the current coding unit being an intra mode, the first coded block flag about the current coding unit is not obtained from the bitstream, and the first coded block flag is identified as indicating that the blocks of the luma component and the chroma components included in the current coding unit comprise one or more non-zero significant transform coefficients in the bitstream.

3. The image decoding method of claim 1 , wherein, based on the first coded block flag indicating that the current coding unit comprises one or more non-zero significant transform coefficients in the bitstream, the identifying of whether the at least one of the height and the width of the current coding unit is greater than the predetermined size comprises identifying whether the height of the current coding unit is greater than a maximum transform unit size or the width of the current coding unit is greater than the maximum transform unit size.

4. The image decoding method of claim 1 , wherein the obtaining of the at least one transform unit included in the current coding unit based on whether the at least one of the height and the width of the current coding unit is greater than the predetermined size comprises, based on the at least one of the height and the width of the current coding unit being greater than the predetermined size, obtaining a plurality of transform units for which at least one of a height and a width has the predetermined size, from the current coding unit.

5. The image decoding method of claim 1 , wherein the obtaining of the first coded block flag from the bitstream comprises, based on the prediction mode of the current coding unit being the inter mode and being neither a merge mode nor a skip mode, obtaining the first coded block flag from the bitstream.

6. The image decoding method of claim 5 , wherein the obtaining the first coded block flag from the bitstream comprises, based on the prediction mode of the current coding unit being the inter mode, and being neither a merge mode nor a skip mode, and a tree type of the current coding unit corresponding to a single tree type, obtaining the first coded block flag from the bitstream.

7. The image decoding method of claim 1 , wherein the obtaining of the second coded block flag from the bitstream comprises, based on a tree type of the current coding unit corresponding to a single tree type or a dual-tree luma type, obtaining the second coded block flag from the bitstream.

8. The image decoding method of claim 1 , wherein the reconstructing of the current image comprising the current coding unit, based on the reconstructed current coding unit, further comprises, when the at least one of the height and the width of the current coding unit is greater than a predetermined second size, performing deblocking filtering on a predetermined boundary location in the current coding unit, the predetermined boundary location being determined based on the predetermined second size.

9. The image decoding method of claim 8 , wherein the performing of the deblocking filtering on the predetermined boundary location in the current coding unit, the predetermined boundary location being determined based on the predetermined second size, comprises obtaining a plurality of blocks for which at least one of a height and a width is a half of the predetermined second size, and performing deblocking filtering on a boundary of the plurality of blocks.

10. The image decoding method of claim 9 , wherein the performing of the deblocking filtering on the boundary of the plurality of blocks comprises:

when a type of an edge to which deblocking filtering is to be performed is a vertical edge, and the width of the current coding unit is greater than the predetermined second size, obtaining the plurality of blocks for which a width is a half of the width of the current coding unit, and performing the deblocking filtering on a vertical boundary of the plurality of blocks; and

when a type of an edge to which deblocking filtering is to be performed is a horizontal edge, and the height of the current coding unit is greater than the predetermined second size, obtaining the plurality of blocks for which a height is a half of the height of the current coding unit, and performing the deblocking filtering on a horizontal boundary of the plurality of blocks.

11. A computer-readable recording medium having recorded thereon a program for implementing the method of claim 1 .

12. The image decoding method of claim 1 , wherein

based on a size of the current coding unit being 128×128, a number of the at least one transform unit is 4, a size of four transform units is 64×64,

based on the size of the current coding unit being 128×N (N is a multiplier of 2 less than 64), a number of the at least one transform unit is 2, a size of two transform units is 64×N, and

based on the size of the current coding unit being N×128 (N is a multiplier of 2 less than 64), a number of the at least one transform unit is 2, a size of two transform units is N×64.