Encoder, decoder, encoding method, and decoding method

An encoding method, comprising:

• in a first encoding process, quantizing a current block using a first quantization matrix in both of a first case where circuitry performs primary transform on the current block and the circuitry does not perform secondary transform on the current block and a second case where the circuitry performs both the primary transform and the secondary transform on the current block,
• in a second encoding process, quantizing the current block using a second quantization matrix in a third case where the circuitry performs primary transform on the current block and the circuitry does not perform secondary transform on the current block, and
• in a third encoding process, quantizing the current block without using a quantization matrix in both of a fourth case where both the primary transform and the secondary transform are skipped for the current block and a fifth case where both the primary transform and the secondary transform are performed on the current block.

A decoding method, comprising:

• in a first decoding process, inverse-quantizing a current block using a first quantization matrix in both of a first case where circuitry performs inverse primary transform on the current block and the circuitry does not perform inverse secondary transform on the current block and a second case where the circuitry performs both the inverse primary transform and the inverse secondary transform on the current block,
• in a second decoding process, inverse-quantizing the current block using a second quantization matrix in a third case where the circuitry performs inverse primary transform on the current block and the circuitry does not perform inverse secondary transform on the current block, and
• in a third decoding process, inverse-quantizing the current block without using a quantization matrix in both of a fourth case where both the inverse primary transform and the inverse secondary transform are skipped for the current block and a fifth case where both the inverse primary transform and the inverse secondary transform are performed on the current block.