Encoding method, decoding method, encoder, and decoder
An encoder includes circuitry and memory. Using the memory, the circuitry performs a primary transform on a derived prediction error, performs a secondary transform on a result of the primary transform, quantizes a result of the secondary transform, and encodes a result of the quantization as data of an image. When a current block to be processed has a predetermined shape, the encoder performs the secondary transform using, among secondary transform basis candidates that are secondary bases usable in the secondary transform, only a secondary transform basis candidate having a size that is not largest size containable in the current block.
1. A decoder comprising:
circuitry; and
memory,
wherein, using the memory, the circuitry:
inverse quantizes data corresponding to a current block of an image;
when the current block is a 4×4 block, performs an inverse secondary transform on a result of the inverse quantization and an inverse primary transform on a result of the inverse secondary transform;
when the current block is larger than a 8×8 block, performs an inverse secondary transform on a part of a result of the inverse quantization and an inverse primary transform on a result of the inverse secondary transform and another part of the result of the inverse quantization; and
derives the image based on a residual signal derived from a result of the inverse primary transform.
2. An encoder comprising:
circuitry; and
memory,
wherein, using the memory, the circuitry:
derives a residual signal of a current block of an image;
when the current block is a 4×4 block, performs a primary transform on the residual signal and a secondary transform on a result of the primary transform;
when the current block is larger than a 8×8 block, performs a primary transform on the residual signal and a secondary transform on a part of the result of the primary transform;
quantizes a result of the secondary transform; and
encodes a result of the quantization.
3. A non-transitory computer readable medium storing a bitstream, the bitstream comprising:
a coded data of a current block on which a decoding process is performed by a decoder, the coded data including a first parameter according to which the decoder selects a second inverse transform basis from among second inverse transform basis candidates:
wherein the decoding process comprises:
inverse quantizing quantized coefficients of the current block;
when the current block is a 4×4 block, performing an inverse secondary transform on a result of the inverse quantization and an inverse primary transform on a result of the inverse secondary transform;
when the current block is larger than a 8×8 block, performing an inverse secondary transform on a part of a result of the inverse quantization and an inverse primary transform on a result of the inverse secondary transform and another part of the result of the inverse quantization; and
deriving an image based on a residual signal derived from a result of the inverse primary transform.
4. A decoding method comprising:
inverse quantizing data corresponding to a current block of an image;
when the current block is a 4×4 block, performing an inverse secondary transform on a result of the inverse quantization and an inverse primary transform on a result of the inverse secondary transform;
when the current block is larger than a 8×8 block, performing an inverse secondary transform on a part of a result of the inverse quantization and an inverse primary transform on a result of the inverse secondary transform and another part of the result of the inverse quantization; and
deriving the image based on a residual signal derived from a result of the inverse primary transform.
5. An encoding method comprising:
deriving a residual signal of a current block of an image;
when the current block is a 4×4 block, performing a primary transform on the residual signal and a secondary transform on a result of the primary transform;
when the current block is larger than a 8×8 block, performing a primary transform on the residual signal and a secondary transform on a part of the result of the primary transform;
quantizing a result of the secondary transform; and
encoding a result of the quantization.