Encoder, decoder, encoding method, and decoding method
An encoder includes circuitry and memory coupled to the circuitry. In residual coding of a current block to which an orthogonal transform is not applied, when coefficient information flags relating to a coefficient in the current block are encoded, the circuitry: performs a level mapping process to transform the coefficient to a second coefficient by using a predicted value, in which the predicted value is determined based on neighboring coefficients of the coefficient within the current block; encodes second coefficient information flags by Context-based Adaptive Binary Arithmetic Coding (CABAC), each of the second coefficient information flags relating to the second coefficient; and encodes a remainder value of the coefficient with Golomb-Rice code, and when the coefficient information flags are not encoded, in operation, the circuitry: skips the level mapping process; and encodes a value of the coefficient with the Golomb-Rice code.
1. 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.
2. 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.