Encoder, decoder, encoding method, and decoding method

A decoder comprising:

• circuitry;
• and
• memory coupled to the circuitry, wherein:
• in residual decoding of a current block to which a reverse-orthogonal transform is not applied, the circuitry:
• when a plurality of coefficient information flags relating to a coefficient in the current block are decoded,
• decodes a plurality of second coefficient information flags by Context-based Adaptive Binary Arithmetic Coding (CABAC) decoding, each of the plurality of second coefficient information flags relating to the coefficient;
• decodes a remainder value of the coefficient with Golomb-Rice decoding;
• reconstructs a value of the coefficient by using the plurality of coefficient information flags, the plurality of second coefficient information flags, and the remainder value;
• and
• performs a reverse-level mapping process to transform the reconstructed coefficient to a second coefficient by using a predicted value, wherein the predicted value is determined based on a plurality of neighboring coefficients of the coefficient within the current block;
• and
• when the plurality of coefficient information flags are not decoded, the circuitry, in operation,
• decodes a value of the coefficient with the Golomb-Rice decoding;
• and
• skips the reverse-level mapping process.

A non-transitory computer readable medium storing a bitstream, the bitstream including information according to which a decoder performs residual decoding, wherein

• in residual decoding of a current block to which a reverse-orthogonal transform is not applied,
• when a plurality of coefficient information flags relating to a coefficient in the current block are decoded,
• a plurality of second coefficient information flags are decoded by Context-based Adaptive Binary Arithmetic Coding (CABAC) decoding, each of the plurality of second coefficient information flags relating to the coefficient;
• a remainder value of the coefficient is decoded with Golomb-Rice decoding;
• a value of the coefficient is reconstructed by using the plurality of coefficient information flags, the plurality of second coefficient information flags, and the remainder value;
• and
• the reconstructed coefficient is transformed to a second coefficient by a reverse-level mapping process using a predicted value, wherein the predicted value is determined based on a plurality of neighboring coefficients of the coefficient within the current block;
• and
• when the plurality of coefficient information flags are not decoded,
• a value of the coefficient is decoded with the Golomb-Rice decoding;
• and
• the reverse-level mapping process is skipped.