Image decoding method, image coding method, image decoding apparatus, image coding apparatus, program, and integrated circuit

An encoding method for encoding an image on a block-by-block basis, the encoding method comprising:

• selecting one prediction mode out of three or more prediction modes;
• encoding a current block to be encoded included in the image by predicting the current block using the selected prediction mode;
• and
• encoding mode information that specifies the selected prediction mode,
• wherein the encoding of the mode information further includes:
• determining one of the three or more prediction modes as a first prediction mode, based on a prediction mode used to predict a neighboring block that is already encoded and adjacent to the current block;
• determining another one of the three or more prediction modes as a second prediction mode that is different from the first prediction mode, the second prediction mode being determined independently from each of prediction modes for neighboring blocks that are adjacent to the current block;
• and
• setting the mode information based on the selected prediction mode and at least one of the first prediction mode and the second prediction mode, and the determining of the second prediction mode includes:
• determining whether or not the first prediction mode is a fixed predefined mode included in the three or more prediction modes, the fixed predefined mode being fixed independently from each of the prediction modes of the neighboring blocks;
• and
• determining the fixed predefined mode as the second prediction mode, when the first prediction mode is not the fixed predefined mode.