Image coding method and image decoding method

An image decoding apparatus for decoding a coded image signal obtained by coding an image per block, the image decoding apparatus comprising:

• a hardware processor;
• and
• a non-transitory memory having a computer program recorded thereon, the computer program when executed by the hardware processor is operable to cause the image decoding apparatus to perform operations comprising:
• receiving the coded image signal;
• performing inverse frequency transform on transform units (i) each of which is an area obtained by partitioning a target block and (ii) each of which is included in the coded image signal, to generate a decoded difference image of the target block;
• performing prediction process on prediction units (i) each of which is an area obtained by partitioning the target block and (ii) each of which is included in the coded image signal, to generate a prediction image of the target block;
• adding the prediction image and the decoded difference image, to generate a decoded image of the target block;
• and
• performing a filtering process on a boundary of the prediction unit in the generated decoded image, when the boundary of the prediction unit is located within a transform unit, the transform unit being an area obtained by partitioning the target block and being a processing unit for frequency transform.