Encoder, decoder, encoding method, and decoding method

A decoder that decodes a moving picture using an inter prediction process, the decoder comprising:

• circuitry configured to perform (i) a first correction process correcting a prediction image of a current block by using luma and chroma of the prediction image and (ii) a second correction process correcting the prediction image of the current block by using spatial gradient of luma of the predicted image;
• and
• memory coupled to the circuitry,
• wherein the circuitry, in operation:
• determines whether to perform the first correction process;
• when the circuitry determines to perform the first correction process, (i) derives a first parameter for the first correction process using the prediction image of the current block and (ii) performs the first correction process on the prediction image of the current block using the first parameter to obtain a final prediction image of the current block;
• when the circuitry determines not to perform the first correction process, the circuitry determines whether to perform the second correction process;
• when the circuitry determines to perform the second correction process, (i) derives a second parameter for the second correction process using the prediction image of the current block and (ii) performs the second correction process on the prediction image of the current block using the second parameter to obtain the final prediction image of the current block;
• and
• when the circuitry determines not to perform the second correction process, uses the prediction image of the current block as the final prediction image of the current block without the circuitry performing a correction process on the prediction image of the current block,
• wherein when the circuitry determines to perform the first correction process, the circuitry performs the first correction process on the prediction image of the current block using the first parameter to obtain the final prediction image of the current block without performing the second correction process on the prediction image of the current block, and
• wherein when the circuitry determines to perform the second correction process, the circuitry performs the second correction process on the prediction image of the current block using the second parameter to obtain the final prediction image of the current block without performing the first correction process on the prediction image of the current block.

An encoding method for encoding a moving picture using an inter prediction process, the encoding method being performed by circuitry configured to perform (i) a first correction process correcting a prediction image of a current block by using luma and chroma of the prediction image and (ii) a second correction process correcting the prediction image of the current block by using spatial gradient of luma of the predicted image, the encoding method comprising:

• determining whether to perform the first correction process;
• when the first correction process is determined to be performed, (i) deriving a first parameter for the first correction process using the prediction image of the current block and (ii) performing the first correction process on the prediction image of the current block using the first parameter to obtain a final prediction image of the current block;
• when the first correction process is not determined to be performed, determining whether to perform the second correction process;
• when the second correction process is determined to be performed, (i) deriving a second parameter for the second correction process using the prediction image of the current block and (ii) performing the second correction process on the prediction image of the current block using the second parameter to obtain the final prediction image of the current block;
• and
• when the first correction process is not determined to be performed, using the prediction image of the current block as the final prediction image of the current block without performing a correction process on the prediction image of the current block,
• wherein when the first correction process is determined to be performed, the first correction process is performed on the prediction image of the current block using the first parameter to obtain the final prediction image of the current block without performing the second correction process on the prediction image of the current block, and
• wherein when the second correction process is determined to be performed, the second correction process is performed on the prediction image of the current block using the second parameter to obtain the final prediction image of the current block without performing the first correction process on the prediction image of the current block.

A decoding method for decoding a moving picture using an inter prediction process, the decoding method being performed by circuitry configured to perform (i) a first correction process correcting a prediction image of a current block by using luma and chroma of the prediction image and (ii) a second correction process correcting the prediction image of the current block by using spatial gradient of luma of the predicted image, the decoding method comprising:

• determining whether to perform the first correction process;
• when the first correction process is determined to be performed, (i) deriving a first parameter for the first correction process using the prediction image of the current block and (ii) performing the first correction process on the prediction image of the current block using the first parameter to obtain a final prediction image of the current block;
• when the first correction process is not determined to be performed, determining whether to perform the second correction process;
• when the second correction process is determined to be performed, (i) deriving a second parameter for the second correction process using the prediction image of the current block and (ii) performing the second correction process on the prediction image of the current block using the second parameter to obtain the final prediction image of the current block;
• and
• when the first correction process is not determined to be performed, using the prediction image of the current block as the final prediction image of the current block without performing a correction process on the prediction image of the current block,
• wherein when the first correction process is determined to be performed, the first correction process is performed on the prediction image of the current block using the first parameter to obtain the final prediction image of the current block without performing the second correction process on the prediction image of the current block, and
• wherein when the second correction process is determined to be performed, the second correction process is performed on the prediction image of the current block using the second parameter to obtain the final prediction image of the current block without performing the first correction process on the prediction image of the current block.