Image encoder, image decoder, image encoding method, and image decoding method

An image decoder comprising:

• circuitry;
• and
• a memory connected to the circuitry,
• wherein the circuitry, in operation,
• decodes a first prefilter or a first postfilter corresponding to the first prefilter, a second prefilter or a second postfilter corresponding to the second prefilter, a first parameter, and a second parameter from a bitstream, decodes a first region of a first image from the bitstream based on the first parameter, and decodes a second region of the first image from the bitstream based on the second parameter, and
• generates a second image by applying a first postfilter corresponding to the first prefilter decoded from the bitstream or the first postfilter decoded from the bitstream to the first region of the first image, and applying a second postfilter corresponding to the second prefilter decoded from the bitstream or the second postfilter decoded from the bitstream to the second region of the first image, and outputs the second image.

An image encoding method comprising:

• by an image encoder,
• determining a first region and a second region in an input image;
• generating a first image from the input image by applying a first prefilter to the first region and applying a second prefilter to the second region;
• determining a first parameter relating to the first region and a second parameter relating to the second region;
• and
• generating a bitstream by encoding the first region based on the first parameter, encoding the second region based on the second parameter, encoding the first prefilter or a first postfilter corresponding to the first prefilter, and encoding the second prefilter or a second postfilter corresponding to the second prefilter.

An image decoding method comprising:

• by an image decoder,
• decoding a first prefilter or a first postfilter corresponding to the first prefilter, a second prefilter or a second postfilter corresponding to the second prefilter, a first parameter, and a second parameter from a bitstream, decoding a first region of a first image from the bitstream based on the first parameter, and decoding a second region of the first image from the bitstream based on the second parameter;
• generating a second image by applying a first postfilter corresponding to the first prefilter decoded from the bitstream or the first postfilter decoded from the bitstream to the first region of the first image, and applying a second postfilter corresponding to the second prefilter decoded from the bitstream or the second postfilter decoded from the bitstream to the second region of the first image;
• and
• outputting the second image.