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

An image decoding apparatus comprising:

• at least one processor configured to:
• determine a current transform unit in a current coding unit;
• determine whether to obtain residual data of the current transform unit by applying or skipping a transformation on the current transform unit;
• when it is determined to obtain the residual data of the current transform by skipping the transformation on the current transform unit, obtain a significant sub-block flag which indicates whether a sub-block in the current transform unit comprises at least one non-zero coefficient or not;
• when the significant sub-block flag indicates that the sub-block comprises at least one non-zero coefficient, obtain at least one of a significant coefficient flag, a sign flag, a first flag and a parity flag by decoding at least one first bin about the significant coefficient flag, the sign flag, the first flag and the parity flag based on a context model, wherein the number of the at least one first bin is equal to or smaller than a number determined based on at least one of width and height of the current transform unit;
• obtain the residual data of the current transform unit, based on at least one of a base level of a coefficient comprised in the sub-block and a remainder excluding the base level from an absolute value of the coefficient, wherein the base level is determined by using the significant coefficient flag, the first flag and the parity flag;
• and
• obtain a reconstruction block of the current coding unit by using the residual data of the current transform unit,
• wherein:
• the significant coefficient flag indicates whether the coefficient is a non-zero coefficient or not,
• the first flag indicates whether the absolute value of the coefficient is greater than a predetermined value or not,
• the parity flag indicates whether the coefficient is an odd number or an even number, and
• the sign flag indicates whether a sign of the coefficient is a positive value or a negative value.

An image encoding method comprising:

• determining a current transform unit in a current coding unit;
• determining whether to obtain residual data of the current transform unit by applying or skipping a transformation on the current transform unit;
• when it is determined to obtain the residual data of the current transform by skipping the transformation on the current transform unit, generating a significant sub-block flag which indicates whether a sub-block in the current transform unit comprises at least one non-zero coefficient or not;
• when the significant sub-block flag indicates that the sub-block comprises at least one non-zero coefficient, generating at least one first bin by encoding at least one of a significant coefficient flag, a sign flag, a first flag, and a parity flag based on a context model, wherein the number of the at least one first bin is equal to or smaller than a number determined based on at least one of width and height of the current transform unit;
• and
• generating a bitstream including the residual data that includes the significant sub-block flag and the at least one first bin,
• wherein:
• the significant coefficient flag indicates whether the coefficient is a non-zero coefficient or not,
• the first flag indicates whether the absolute value of the coefficient is greater than a predetermined value or not,
• the parity flag indicates whether the coefficient is an odd number or an even number, and
• the sign flag indicates whether a sign of the coefficient is a positive value or a negative value.

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

• determining a current transform unit in a current coding unit;
• determining whether to obtain residual data of the current transform unit by applying or skipping a transformation on the current transform unit;
• when it is determined to obtain the residual data of the current transform by skipping the transformation on the current transform unit, generating a significant sub-block flag which indicates whether a sub-block in the current transform unit comprises at least one non-zero coefficient or not;
• when the significant sub-block flag indicates that the sub-block comprises at least one non-zero coefficient, generating at least one first bin by encoding at least one of a significant coefficient flag, a sign flag, a first flag, and a parity flag based on a context model, wherein the number of the at least one first bin is equal to or smaller than a number determined based on at least one of width and height of the current transform unit;
• and
• generating a bitstream including the residual data that includes the significant sub-block flag and the at least one first bin,
• wherein:
• the significant coefficient flag indicates whether the coefficient is a non-zero coefficient or not,
• the first flag indicates whether the absolute value of the coefficient is greater than a predetermined value or not,
• the parity flag indicates whether the coefficient is an odd number or an even number, and
• the sign flag indicates whether a sign of the coefficient is a positive value or a negative value.