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

An image decoding apparatus comprising:

• at least one processor configured to:
• obtain a plurality of largest coding units by splitting a current image based on a size information of a largest coding unit;
• obtain 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;
• when a merge flag indicates that a prediction mode of the current coding unit is a merge mode, determine motion information of the current block based on previously-decoded motion information without obtaining the motion information of the current block from a bitstream;
• when the prediction mode of the current coding unit is the merge mode, determining a first coded block flag indicates the current coding unit comprises one or more non-zero significant transform coefficients without obtaining the first coded block flag from the bitstream, wherein the first coded block flag is not included in the bitstream;
• when the first coded block flag indicates that the current coding unit comprises one or more non-zero significant transform coefficients, identify 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, obtain at least one transform unit included in the current coding unit;
• when the at least one of the height and the width of the current coding unit is greater than the predetermined size, obtain, from the bitstream, a 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;
• obtain 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;
• reconstruct the current coding unit based on the residual signal;
• and
• reconstruct 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,
• wherein the at least one largest coding unit is a square shape.

An image encoding method comprising:

• obtaining a plurality of largest coding units by splitting a current image based on a size 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;
• when a prediction mode of the current coding unit is a merge mode, determining motion information of the current block based on previously-determined motion information;
• when the prediction mode of the current coding unit is the merge mode, determining a first coded block flag indicates the current coding unit comprises one or more non-zero significant transform coefficients, wherein the first coded block flag is not included in the bitstream;
• based on determining 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;
• encoding residual signal of a block of luma component included in the at least one transform unit;
• when the at least one of the height and the width of the current coding unit is greater than the predetermined size, generating a 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;
• and
• generating a bitstream including a merge flag indicating the prediction mode of the current coding unit is the merge mode, the encoded residual signal, and the second coded block flag;
• 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,
• wherein the at least one largest coding unit is a square shape.

A non-transitory computer-readable storage medium storing a bitstream, the bitstream being encoded by an encoding method comprising:

• obtaining a plurality of largest coding units by splitting a current image based on a size 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;
• when a prediction mode of the current coding unit is a merge mode, determining motion information of the current block based on previously-determined motion information;
• when the prediction mode of the current coding unit is the merge mode, determining a first coded block flag indicates the current coding unit comprises one or more non-zero significant transform coefficients, wherein the first coded block flag is not included in the bitstream;
• based on determining 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;
• encoding residual signal of a block of luma component included in the at least one transform unit;
• when the at least one of the height and the width of the current coding unit is greater than the predetermined size, generating a 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;
• and
• generating a bitstream including a merge flag indicating the prediction mode of the current coding unit is the merge mode, the encoded residual signal, and the second coded block flag;
• 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,
• wherein the at least one largest coding unit is a square shape.